Sharovipteryx and the Origin of Pterosaurs

The bizarre hind-wing glider, Sharovipteryx mirabilis, has confounded and intrigued paleontologists since 1971 when Alexander G. Sharov first described it. The most prominent aspects of the fossil are the extremely long hind limbs, trailed by extensive extradermal membranes called uropatagia. While several readily visible aspects of Sharovipteryx immediately recall pterosaurs (attenuated tail, longer tibia than femur, hollow bones, elongated ilium. sacrum of way more than two vertebrae, elongated pedal 5.1, dermal membranes, among others), the reduced forelimbs were cause for concern in a pterosaur sister taxon.

 

Sharovipteryx mirabilis

Figure 1. Sharovipteryx mirabilis in various views. Click to learn more.

Poorly preserved?
Sharovipteryx
has been described as “poorly preserved” even though the finest details are preserved in its extradermal membranes. The skull is crushed, but all the details are visible. Insects are preserved with and within Sharovipteryx. A beetle lies nearby. A winged ant or wasp is found in the skull. Shcherbakov (2008) described the Lagerstätte formation from which Sharovipteryx was found. The paleoenvironment (Madygen Formation, Osh Region in Kyrgyzstan, Early Triassic, 228 mya) may be reconstructed as an intermontane river valley in seasonally arid climate, with mineralized oxbow lakes and ephemeral ponds on the floodplain. After amber, it may be the best formation for preserving insects.

Early Errors
Peters (2000) attempted to trace the skull elements of Sharovipteryx, but I assumed the split at the back of the skull must have been a pterygoid. Instead it represents a domed cranium. In my rookie year as a paleontologist, I made several mistakes, this one among them. Later I was able to discern and correct my error. I also found more elements of the forelimb. All these can be seen here. No one else has attempted a detailed tracing and identification of the elements before or since.

Subsequent Corrections
There is word that some further preparation has occurred, according to Hone and Benton (2007), who reported, “In any case, the true arms of Sharovipteryx have now been found buried in the matrix (R. R. Reisz, pers. comm., 2003) and this confirms that Peters (2000) supposed arm was incorrectly identified.” It is not clear that Hone and Benton (2007) actually had access to the data itself, but in their zeal to discredit Peters (2000) they latched onto this hearsay. Unfortunately, the Reisz data have not been made available and have not been published in the eight years that have followed. Concurrently, as mentioned earlier, I was able to correct earlier mistakes. The forelimb elements I found matched left to right and fell in line in all morphological aspects between the two sister taxa of Sharovipteryx, Cosesaurus and Longisquama (Peters 2006). These included a tiny pteroid and preaxial carpal, bones otherwise found only in fenestrasaurs, including pterosaurs. I also identified prepubic bones and a hyper-elongated ilium in Sharovipteryx. These traits are also restricted to fenestrasaurs including pterosaurs. Prepubes acted like elongated pubes, adducting the sprawling hind limbs.

The pelvis and prepubes of Sharovipteryx.

Figure 2. The pelvis and prepubes of Sharovipteryx.

Truncated Studies
Following his  studies of the uropatagia in Sordes (Unwin DM and Bakhurina NN 1994), Dr. David Unwin (2000a, b, c) flirted briefly with Sharovipteryx as a pterosaur sister taxon, but has ignored it ever since. Unfortunately in his update he used Sharov’s own figure from 1971, rather than providing an updated figure.

In his book, The Pterosaurs From Deep Time, Unwin 2006 asked if Sharovipteryx could be ancestral to pterosaurs, then answered, “Probably not. Because it is almost the same geological age as early pterosaurs and, with its remarkably long neck, already highly specialized.” While referencing nearly every other paper and worker on pterosaurs, all papers written by yours truly (Peters 2000 and 2002 among them) were overlooked and ignored. Rather he opted to continue the old paradigm that, “pterosaurs sit in splendid isolation, definitely related to, but somehow remote from, other diapsids.” Unwin said there was no antorbital fenestra and the arms were extraordinarily short and small. While the latter is true, the former is not. Unwin never performed a cladistic analysis with Sharovipteryx and other pterosaur ancestor candidates to test the results of Peters (2000).

Following Gans et al. (1987), Dyke et al. (2006) described Sharovipteryx as a “delta-wing” flyer. Unfortunately they provided no evidence of membranes anterior to the hindlimb, but imagined them instead.

With such small forelimbs and such long hindlimbs, Sharovipteryx would have been a full-time biped, a fact that has been largely overlooked. As a biped, Sharovipteryx could have done other things with its forelimbs, such as gliding and flapping.

Sharovipteryx would have been a consummate glider. The enlarged hyoids extended the neck skin into strakes (leading edge root extensions), an aerodynamic structure found on several modern jet fighters. The ribs extended laterally, forming a small round pancake. Manual digit 4 extended further than the other digits. Since both sister taxa (Cosesaurus and Longisquama) had trailing edge membranes, it is likely that Sharovipteryx also had them. Rather than a delta wing, the membranes had a deeper chord distally, creating a canard wing configuration.

Due to the stem-like coracoid and strap-like scapula, Sharoviptyerx likely flapped its forelimbs, not only to show excitement and attract attention when grounded, but to create thrust and lift when aloft. The large, fiber embedded uropatagia that trailed the sprawling hind limbs of Sharovipteryx provided the majority of lift and extended through the center of balance. Other tiny membranes extended anterior to the lower tibia and mid femur. Longisquama was similar in configuration, but with longer forelimbs. Pterosaurs were also similar, but with even longer wing fingers.

The hind legs of Sharovipteryx provide a good model for the configuration of most pterosaurs, sprawling in flight. On land, whenever the knees were lower than the hip socket, which was probably typical, the right angled knees returned the ankles to beneath the torso, as in pterosaurs.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Dyke G, Nudds RL and Rayner JMV 2006. Flight of Sharovipteryx mirabilis: the world’s first delta-winged glider. Journal of Evolutionary Biology.
Gans C, Darevski I, and Tatarinov LP 1987. Sharovipteryx. A reptilian glider? Paleobiology 13(4):415–426.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Peters, D. 2000b. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7(1):11-41.
Peters D 2000.
 
A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing—with a twist. Historical Biology 15:277-301.
Peters D 2006. The Front Half of Sharovipteryx. Prehistoric Times 76: 10-11.
Shcherbakov DE 2008. Madygen, Triassic Lagerstätte number one, before and after Sharov. Alavesia 2:113-124. online pdf
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sharov AG 1971. New flying reptiles from the Mesozoic of Kazakhstan and Kirghizia. – Transactions of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
Unwin DM 2000a. Sharovipteryx: what can it tell us about the origin of pterosaurs?
48th Symposium of Vertebrate Palaeontology and Comparative Anatomy, Portsmouth,
England, Monday 28 Aug. – Sunday 3 September.
(http://www.soft.net.uk/richardforrest/svpca2000/svpca2000.page.intro.html)
Unwin DM 2000b. Sharovipteryx and its significance for the origin of the pterosaur
flight apparatus. 5th European Workshop on Vertebrate Palaeontology, 27.6.2000
– 1.7.2000, Staatliches Museum für Naturkunde Karlsruhe (SMNK) Erbprinzenstr.
13 D-76133 Karlsruhe Germany (http://www.alettra.de/ewvp5/index.htm)
Unwin DM 2006. The Pterosaurs from Deep Time. Pi Press, New York, NY.
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.
Unwin DM, Alifanov VR and Benton MJ 2000. Enigmatic small reptiles from the Middle Triassic of Kirgizia, pp. 177–186. In: Benton M. J., Unwin D. M. & Kurochin E. “The age of Dinosaurs in Russia and Magnolia”, Cambridge University Press, Cambridge.

Longisquama and the Origin of Pterosaurs

Prequel: Longisquama Gets No Respect
(or the Lengths Scientists Will Go to Protect Pet Theories)

In their two-part paper on pterosaur origins Hone and Benton (2007, 2008) announced they would test whether pterosaurs nested more parsimoniously within the Archosauria (Bennett 1996) or the Prolacertiformes (Peters 2000). They used the technique of the supertree, gathering several trees together to come up with a larger, ostensibly more complete, tree. That permitted them to use the data of others without having to visit fossils. We’ll get back to their results (below), but first a short background study.

Bennett (1996) used suprageneric taxa, for the most part, and nested pterosaurs with Scleromochlus at the base of the Dinosauria + Lagosuchus (now Marasuchus). The Ornithosuchidae were basal to this clade. The Prolacertiformes were nested far toward the base of the tree. Earlier we discussed problems with these putative sisters here. Bennett (1996) did not consider CosesaurusSharovipteryx and Longisquama.

Fenestrasaurus

Figure 1. Click to enlarge. Fenestrasaurs including Cosesaurus, Sharovipteryx, Longisquama and pterosaurs

Peters (2000) tested the matrices of Bennett (1996) and two others (Jalil 1991 and Evans 1986) simply by adding Langobardisaurus and the fenestrasaurs, including CosesaurusSharovipteryx and Longisquama. Pterosaurs nested with these taxa, rather than any archosaur or archosauromorph, when given the opportunity. Peters (2000) erected the clade, the Fenestrasauria, because they shared the trait of an antorbital fenestra without a fossa, convergent with that of archosaurs.

The largest study to date on reptile interrelationships nested Longisquama and pterosaurs with lizards like Lacertulus, Meyasaurus and Huehuecuetzpalli, far from Prolacerta, archosauromorphs, Scleromochlus and archosaurs.

Getting Back to Where We Began
Hone and Benton (2007) discredited the data of Peters (2000) and elected not to include any of it in their supertree. That left only one study that included pterosaurs, Bennett (1996), in their supertree analysis. Having eliminated the opposing candidate data and the opposing candidate taxa, the results were predetermined. The results of Hone and Benton (2008) reflected the results of Bennett (1996). Sadly, the results also nested members of the Choristodera far from the Choristodera and members of the Lepidosauromorpha far from the Lepidosauromorpha, so the study had its problems. Moreover, Hone and Benton (2008) falsely gave credit for the prolacertiform hypothesis to Bennett (1996), after properly giving it to Peters (2000) in their earlier (2007) paper. And now you know  the lengths scientists will go to protect their pet theories.

The Back Half of Longisquama
Ever since Sharov (1971) reported that only the front half of Longisquama was visible, scientists stopped looking for it. Ironically, one of the plumes illustrated by Sharov(1971), the one not radiating like the others, was a tibia and femur. The subdivided “feather shafts” reported by Jones et al. (2000) were actually displaced toes subdivided by phalanges. Here, using the technique of DGS (digital graphic segregation) the back half of Longisquama is, at last, revealed.

The complete fossil of Longisquama.

Figure 2. Click to enlarge. The complete fossil of Longisquama.

The back half of Longisquama was overlooked for so long because the elements lined up with and were camouflaged by the plumes. Apparently Longisquama’s stomach exploded, or was torn up. The front third of Longisquama is undisturbed, the tail is undisturbed, but the hips are turned backwards and the legs and feet are rotated up to the dorsal vertebrae.

Longisquama in lateral view

Figure 3. Longisquama in lateral view, dorsal view and closeup of the skull. Like Microraptor, Longisquama glided/flew with similarly-sized wings both fore and aft.

Distinct from Cosesaurus
The skull of Longsiquama had a more constricted snout, which enhanced binocular vision. The orbits were larger. The teeth had larger cusps. The naris was probably larger. With increased bipedalism and active flapping, Longiquama probably experimented with aerobic metabolism. The cervicals were shorter and the dorsal series was longer, especially so near the hips and between the ilia. The sacrum curved dorsally 90 degrees, which elevated the attenuated tail. These vertebral modifications made Longsiquama similar to a lemur, which also leaps from tree to tree. Such a long torso provided more room for plumes, gave the back great flexibility, and provided more room for egg production. The pectoral girdle was little changed from Cosesaurus. The clavicles curved around the sternal complex and the sternal keel was deeper. Fused together the interclavicle, clavicles and sternum form a sternal complex, as in pterosaurs. During taphonomy the sternal complex ofLongisquama drifted to beneath the cervicals, exactly where the clavicles are found in non-fenestrasaur tetrapods, including birds. This has led to confusion because the clavicles overlapped giving the appearance of a bird-like furcula. As in Cosesaurus, the pterosaur-like pectoral girdle and socketed coracoids enabled Longisquama to flap and generate thrust during leaps. The pelvis was greatly elongated anteriorly and posteriorly with a posterior ilium rising along with the dorsally curved sacrum of seven vertebrae. The pubis and ischium were much deeper, which provided a much larger pelvic aperture to pass a much larger egg. The distal femur was concave and the proximal tibia convex, as in Sharovipteryx. Both the femur and tibia/fibula were more robust. The foot was relatively large with digits of increasing length laterally. Pedal digit V had a curved proximal phalanx.

Longisquama is famous for, and was named for, its dorsal plumes. Another set of plumes arose from its skull and neck. Former caudal hairs (in Cosesaurus) formed a tail vane in Longisquama. As in Sharovipteryx and pterosaurs, Longsiquama had a uropatagium trailing each of its hind limbs. Like Cosesaurus, Sharovipteryx and pterosaurs membranes trailed the forelimbs, too. This documents the origin of the pterosaur wing and proves that it developed distally on a flapping wing (Peters 2002) rather than proximally as a gliding membrane (contra Elgin, Hone and Frey in press) and certainly without wing pronation, loss of digit V, loss of ungual 4 and migration of metacarpals I-III to the anterior face of metacarpal IV (contra Bennett 2008).

Longisquama was overloaded with secondary sexual characteristics. From plumes to flapping arms, Longisquama was all about creating an exciting presentation unrivaled until the present-day bird-of-paradise. Longisquama had everything Cosesaurus had, only wildly exaggerated. With increased bipedalism and active flapping, Longiquama probably experienced the genesis of aerobic metabolism.

Figure 4. Click to enlarge. The origin of the pterosaur wing and the migration of the pteroid and preaxial carpal. A. Sphenodon. B. Huehuecuetzpalli. C. Cosesaurus. D. Sharovipteryx. E. Longisquama. F-H. The Milan specimen MPUM 6009, a basal pterosaur.

The Origin of the Pterosaur Wing
The elongated and robust finger four of Longisquama was also overlooked by all prior workers. Reconstructed here the hand of Longsiquama remains the best transitional example between Cosesaurus and pterosaurs. It is likely that digit 4 did not flex with the other three fingers in Longisquama because the PILs (parallel interphalangeal lines) were not continuous through digit 4, which also supported a pterosaur-like wing membrane, preserved along with the other soft tissue, the plumes.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. Hone (eds.), Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica doi: 10.4202/app.2009.0145 online pdf
Jones TD et al 2000. Nonavian Feathers in a Late Triassic Archosaur. Science 288 (5474): 2202–2205. doi:10.1126/science.288.5474.2202. PMID 10864867.
Martin LD 2004. A basal archosaurian origin for birds. Acta Zoologica Sinica 50(6): 978-990.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, DeKalb, IL, 1-279.
Senter P 2004. Phylogeny of Drepanosauridae (Reptilia: Diapsida) Journal of Systematic Palaeontology 2(3): 257-268.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

wiki/Longisquama

The Family Tree of the Pterosauria 19 – The Ornithocheiridae part 3 of 3

In part 1 of the Ornithocheiridae we looked at the base of this large clade of long-winged soaring pterosaurs. In part 2 we looked at ColoborhynchusIstiodactylus and their kin. Here in part 3 look at more derived taxa such as Anhanguera and Liaoningopterus.

The Ornithocheiridae.

Figure 1. The Ornithocheiridae. Click to enlarge and expand.

We’ll Continue with Brasileodactylus
Brasileodactylus araripensis AMNH 24444 (Kellner, 1984; Veldmeijer 2003b) was originally described from just the anterior jaws and later a complete skull and other elements were found. It was derived from a sister to Coloborhynchus  and Haopterus (see part 1), skipping the istiodactylid clade (part 2). Distinct from Coloborhynchus, the skull of Brasileodactylus had no crest. The posterior premaxillary teeth were quite long. So were the matching dentary teeth. The squamosal had a dorsal process that gave the lateral temporal fenestra the appearance of a human ear. The lacrimal protruded into the orbit. The jugal was expanded anteriorly into the antorbital fenestra. The antorbital fenestra was shorter.

Barbosania 
Barbosania gracilirostris (Elgin and Frey 2011) was considered close to Brasileodactylus and was similar in size. The original report stated, “While elements of the cranium appear to suture very early in ontogeny (Kellner and Tomida 2000) all ornithocheiroids recovered from the Romualdo Member of the Santana Formation are considered to be ontogenetically immature based on the lack of fusion in the postcranial skeleton.” Actually this is a phylogenetic signal. As derived lizards, pterosaurs did not follow archosaur fusion patterns.

Ludodactylus.

Figure 2. Click to enlarge. Ludodactylus.

Ludodactylus
Ludodactylus sibbicki SMNK PAL 3828 (Frey, Martill and Buchy 2003) is known from a skull with the unusual combination of a cranial crest and teeth. Distinct from Brasileodactylus, the skull of Ludodactylus was shorter overall with a parietal (cranial) crest with a frontal leading edge. The jugal was not expanded into the antorbital fenestra. The orbit was narrower. The postorbital was more robust. The mandible was more robust and was upturned anteriorly with smaller teeth posteriorly.

Cearadactylus
Cearadactylus atrox 
formerly: SMNK PAL 3828 and CB-PV-F-O93, now: UFRJ MN 7019-V (Leonardi and Borgomanero 1985) Cenomanian, Early Cretaceous, ~90 mya, ~57 cm skull length is known from a skull with an unusual history. Originally it was put together with the premaxilla and anterior dentary switched. Distinct from Brasileodactylus, the skull of Cearadactylus had a wide spoonbill or rosette tip from which erupted giant teeth. The maxillary teeth were tiny. The mandible was deeper, but flatter anteriorly.

Cearadactylus ligabuei CCSRL 12692/12713 (Dalla Vecchia 1993) was similar but had a distinctly shorter rostrum and smaller teeth with an upturned premaxilla. The tip was not a spoonbill, but the middle of the rostrum was narrowed or pinched in dorsal view. The jugal was more gracile.

Liaoningopterus

Figure 3. Click to enlarge. Liaoningopterus

Liaoningopterus
Liaoningopterus gui IVPP V 13291 (Wang and Zhou 2003) Cenomanian, Early Cretaceous, ~90 mya, ~61 cm skull length. Distinct from Cearadactylus, the skull of Liaoningopterus was low anteriorly and very tall posteriorly. A very low crest surmounted the snout tip. Only one premaxillary tooth was enlarged to fang status. It is the largest tooth known for any pterosaur. The anterior dentary was expanded.

Anhanguera

Figure 4. Click to enlarge. Anhanguera.

Anhanguera
Anhanguera piscator IVPP V 13291 (A. bittersdorffi No. 40 Pz-DBAV-UERJ Campos & Kellner, 1985; A. santanae AMNH 22555 Wellnhofer 1985; A. piscator, Kellner and Tomida 2000) Aptian, Early Cretaceous ~110 mya, ~60 cm skull length. Distinct from Liaoningopterus, the skull of Anhaguera had a longer premaxillary crest and smaller teeth. The anterior dentary formed a keel. The squamosal did not rise to form an “ear” shape of the lateral temporal fenestra. The tail was robust and had elongated vertebrae distally. Distinct from Brasileodactylus, manual 4.1 extended to the elbow when folded. Postcranially Anhanguera was most similar to SMNS PAL 1136, but without such a deep sternal complex keel and deep torso. The foot had very short metatarsals and elongated phalanges.

In Summary
The Ornithocheiridae is one of the few pterosaur clades without tiny members. Then again, from Yixianopterus at the base to Anhanguera as the most derived taxon, the morphology of this clade did not go through major changes. Trends toward the development and loss of a snout tip crest, more robust forelimbs and more gracile hindlimbs, an increase in the size of the antorbital fenestra in istiodactylids are all apparent. From the wing/leg ratios it seems apparent that this clade spent more time on the wing and less on the ground. Take-off was likely into the wind with a minimum take-off run from locations near steady and constant ocean breezes. A lack of skeletal fusion (sacrals, scapula/coracoid) permeates this clade, with some of the largest specimens lacking fusion. Fusion did affect some members, but the pattern was phylogenetic, not ontogenetic. The warped deltopectoral crest exhibited by some ornithocheirids has linked them to Pteranodon, but the morphology is distinct and the development was by convergence.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Campos, D de A and Kellner AW 1985. Un novo exemplar de Anhanguera blittersdorffi(Reptilia, Pterosauria) da formaçao Santana, Cretaceo Inferior do Nordeste do Brasil.” In Congresso Brasileiro de Paleontologia, Rio de Janeiro, Resumos, p. 13.
Dalla Vecchia FM 1993. Cearadactylus? ligabuei, nov. sp., a new Early Cretaceous (Aptian) pterosaur from Chapada do Araripe (Northeastern Brazil)”, Bolletini della Societa Paleontologica Italiano, 32: 401-409.
Elgin RA and Frey E 2011. A new ornithocheirid, Barbosania gracilirostris gen. et sp. nov. (Pterosauria, Pterodactyloidea) from the Santana Formation (Cretaceous) of NE Brazil. Swiss Journal of Palaeontology. DOI 10.1007/s13358-011-0017-4.
Frey E, Martill DM and Buchy M-C 2003. A new crested ornithocheirid from the Lower Cretaceous of northeastern Brazil and the unusual death of an unusual pterosaur: In: Buffetaut, E., and J.-M. Mazin, Eds. Evolution and Palaeobiology of Pterosaurs. – London, Geological Society Special Publication 217: p. 55-63.
Kellner AWA 1984. Ocorrência de uma mandibula de pterosauria (Brasileodactylus araripensis, nov. gen.; nov. sp.) na Formação Santana, Cretáceo da Chapada do Araripe, Ceará-Brasil. Anais XXXIII Cong. Brasil. de Geol, 578–590. Rio de Janeiro
Kellner AWA and Tomida Y 2000. Description of a new species of Anhangueridae (Pterodactyloidea) with comments on the pterosaur fauna from the Santana Formation (Aptian–Albian), Northeastern Brazil. National Science Museum Monographs, 17:1–135.
Leonardi G and Borgomanero G 1985. Cearadactylus atrox nov. gen., nov. sp.: novo Pterosauria (Pterodactyloidea) da Chapada do Araripe, Ceara, Brasil. Resumos dos communicaçoes VIII Congresso bras. de Paleontologia e Stratigrafia, 27: 75–80.
Unwin DM 2002. On the systematic relationships of Cearadactylus atrox, an enigmatic Early Cretaceous pterosaur from the Santana Formation of Brazil. Mitteilungen Museum für Naturkunde Berlin, Geowissenschaftlichen Reihe 5: 1239–263.
Veldmeijer AJ 2003b. Preliminary description of a skull and wing of a Brazilian Cretaceous (Santana Formation; Aptian-Albian) pterosaur (Pterodactyloidea) in the collection of the AMNH. PalArch, series vertebrate palaeontology 1: 1-13.
Veldmeijer AJ, Meijer HJM and SignoreM 2009. Description of Pterosaurian (Pterodactyloidea: Anhangueridae, Brasileodactylus) remains from the Lower Cretaceous of Brazil, DEINSEA 13: 9-40
Vila Nova BC, Kellner AWA, Sayão JM 2010. Short Note on the Phylogenetic Position of Cearadactylus Atrox, and Comments Regarding Its Relationships to Other Pterosaurs. Acta Geoscientica Sinica 31 Supp.1: 73-75.
Wellnhofer P 1985. Neue Pterosaurier aus der Santana-Formation (Apt) der Chapada do Araripe, Brasilien. Paläontographica A 187: 105–182.

The Family Tree of the Pterosauria 18 – The Ornithocheiridae part 2 of 3

In part 1 of the Ornithocheiridae we looked at the base of this large clade of long-winged soaring pterosaurs. Here in part 2 we’ll look at ColoborhynchusIstiodactylus and their kin. These taxa form a clade of their own, a little off to the side. In part 3 we will start again where we ended in part 1 and examine more derived taxa such as Anhanguera and Liaoningopterus.

The Ornithocheiridae.

Figure 1. The Ornithocheiridae. Click to enlarge and expand.

We’ll Continue with Coloborhynchus
Coloborhynchus spielbergi (Owen 1874, = Ornithocheirus clavirostris; C. spielbergi Veldmeijer 2003) RGM 401 880, Early Cretaceous was originally lumped with Ornithocheirus and much later was considered congeneric with Anhanguera by several workers (Kellner 2006). Distinct from Haopterus, the skull of Coloborhynchus had an anterior crest both above the snout and below the chin. The pre-antorbital fenestra region was longer. The orbit was narrower and raised higher over the antorbital fenestra. The neural spines were taller. A notarium was formed by several fused dorsals into which the scapula was articulated. The sacrals were interlocked if not fused. The sternal complex was rather deep. The scapulocoracoid was fused. The humerus was much more gracile. The ulna and radius were also thinner, but the distal ends were expanded. The pelvis was more robust with a more ossified ischium and a raised posterior ilium.

Criorhynchus 
Criorhynchus mesembrinus (Owen 1874, = Ornithocheirus clavirostris; = Tropeognathus mesembrinus, Fastnacht 2001) BSp 1987 I 46 from the Early Cretaceous was a sister to Coloborhynchus and may be congeneric with it. Distinct from Coloborhynchus, the skull of Criorhynchus was longer, lower and wider. The palatal elements were more robust. The ischium was narrower.

Nurhachius, a Basal Istiodactylid
Nurhachius ignaciobritoi (Wang, Kellner, Zhou & Campos 2005) IVPP V-13288, Early Cretaceous, skull length ~30 cm, ~2.5 m wingspan. Distinct from Criorhynchus the skull of Nurhachius further extended the rostrum and increased the size of the antorbital fenestra. If predecessors had a crest, it was greatly reduced or underdeveloped in Nurhachius. The orbit was very narrow and posteriorly slanted with a tiny sclerotic ring at the top. The upper temporal fenestra was completely above the orbit. Distinct from Coloborhynchus, the sternal keel was very deep (if that is the keel). The humerus was shorter. Fingers 1-3 were smaller. The femur was shorter. The metatarsals were robust and the pedal digits were slender, as in Zhenyuanopterus.

The largest ornithocheirid

Figure 2. Click to enlarge. The unnamed largest ornithocheirid, SMNK PAL 1136

One of the Biggest Ornithocheirids Still Has No Name
SMNK PAL 1136 (not yet described, figured by Frey and Marill 1994) ~80 cm skull length, Aptian, Early Cretaceous ~130 mya, was originally considered an Anhanguera sp. Larger and distinct from Istiodactylus, the skull of SMNK PAL 1136 had the antorbital fenestra extend into the anterior rostrum just posterior to the premaxillary crest. The orbit was high and small. It was located just aft of the mandibular articulation. The jugal + lacrimal were reduced to slender rods oriented dorsoposteriorly. The sternal complex had a large keel and a reduced sternal plate. The scapulocoracoid was gracile. The gracile humerus expanded distally. Manual 4.1 extended to the elbow when folded. The pelvis was relatively smaller than in Coloborhynchus and the prepubis is tiny. The femur was considerably shorter than the tibia.

Istiodactylus latidens
Istiodactylus latidens BMNH R 3877 (Hooley 1913, Ornithodemus” latidens; Howse, Milner and Martill 2001) ~56 cm skull length, Aptian, Early Cretaceous ~130 mya was an unusual ornithocheirid known from a partial skeleton. Distinct from SMNK PAL 1136, the skull of Istiodactylus was a quarter smaller than SMNK 1136 PAL and similar in size to Coloborhynchus. The long gracile skull was dominated by an antorbital fenestra comprising 63 per cent of its estimated length. The anterior margin of the antorbital fenestra was posterior to all teeth, which fill only the anterior fourth of the jaws. Both narial openings (per side) were dorsal to the teeth. The long quadrates were so inclined that the orbit was positioned even further posteriorly than in PAL 1136. The teeth were lancet-shaped, closely spaced, and interlocked like a bear trap. A central dentary tooth filled the gap left by the medial premaxilla teeth, which were diminutive. The teeth increased in size posterolaterally. Two posterior dentary teeth fit into slots in the premaxilla. The dorsal vertebral transverse processes were nearly vertical. A notarium of six vertebrae was present. Asymmetrical coracoidal articulations on the anterior edge of the deep sternal complex keel continued on the lateral surface. The reconstructed wing/torso ratio was estimated at ~9:1. The deltopectoral crest was warped into a spiral. The ulna had a ridge that supported the radius. The antebrachium was relatively longer than in PAL 1136. What Hooley (1913) identfied as an ischium is identified here as the pubis and ischium.

Istiodactylus

Figure 3. Click to enlarge. Istiodactylus

Istiodactylus sinensis
Istiodactylus sinensis 
NGMC 99-07-011 (Andres and Ji 2006) Aptian, Early Cretaceous ~125 mya, ~35 cm skull length, appears to be more primitive in that the deltopectoral crest was not so curved and the skull was not as gracile. As in Nurhachius, when the wing was folded the elbow was closest to the middle of m4.2. The three free fingers each had only one phalanx, probably via fusion because there is no dimunition of the finger lengths. The resulting proximal phalanges are all subequal, approaching the configuration in Coloborhynchus, which had no phalanx fusion. Only pedal digit I and IV are known and they follow the pattern of larger medial digits seen in sister taxa.

In summary
This clade originated with a big crest on the rostrum tip and a small antorbital fenestra. As taxa evolved the crest slowly disappeared while the antorbital fenestra elongated anteriorly and pushed the orbit higher and smaller posteriorly.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Andres B and Ji Q 2006. A new species of Istiodactylus (Pterosauria, Pterodactyloidea) from the Lower Cretaceous of Liaoning, China. Journal of Vertebrate Paleontology, 26: 70-78.
Bowerbank JS 1846. On a new species of pterodactyl found in the Upper Chalk of Kent P. giganteus). Quarterly Journal of the Geological Society 2: 7–9.
Bowerbank JS 1851. On the pterodactyles of the Chalk Formation. Proceedings of the Zoological Society, London, pp. 14–20 and Annals of the Magazine of Natural History (2) 10: 372–378.
Bowerbank JS 1852. On the pterodactyles of the Chalk Formation. Reports from the British Association for the Advancement of Science (1851): 55.
Fastnacht M 2001. First record of Coloborhynchus (Pterosauria) from the Santana Formation (Lower Cretaceous) of the Chapada do Araripe, Brazil. – Palaontologische Zeitschrift 75(1): 23-36.
Frey E and Martill DM 1994. A new Pterosaur from the Crato Formation (Lower Cretaceous, Aptian) of Brazil. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 194: 379–412.
Hooley RW 1913. On the skeleton of Ornithodesmus latidens. An ornithosaur from the Wealden shales of Atherfield (Isle of Wight)”, Quarterly Journal of the Geological Society, 69: 372-421
Howse SCB, Milner AR and Martill DM 2001. Pterosaurs. Pp. 324-335 in: Martill, D. M. and Naish, D., eds. Dinosaurs of the Isle of Wight, The Palaeontological Association
Owen R 1861. Monograph on the fossil Reptilia of the Cretaceous Formations. Supplement III. Pterosauria (Pterodactylus). The Palaeontographical Society, London. (volume for 1858; pp. 1–19 & pls 1–4)
Owen R 1874. A Monograph on the Fossil Reptilia of the Mesozoic Formations. 1. Pterosauria. The Palaeontographical Society, London. pp. 1–14 & pls 1–2.
Wang X, Kellner AWA, Zhou Z and Campos DA 2005. Pterosaur diversity and faunal turnover in Cretaceous terrestrial ecosystems in China. Nature 437 (7060): 875–879. doi:10.1038/nature03982. PMID 16208369.

The Family Tree of the Pterosauria 17 – The Ornithocheiridae part 1 of 3

We just looked at one branch of descendants from Scaphognathus (No. 110) and Gmu 10157 that ultimately produced Cycnorhamphus and Feilongus. Here we look at the other branch of Scaphognathus No. 110 descendants, the Ornithocheiridae in three parts. Part 1 (below) will look at basal taxa. Part 2 will look at Coloborhynchus, Istiodactylus and their kin. Part 3 will look at more derived taxa such as Anhanguera and Liaoningopterus.

The Ornithocheiridae.

Figure 1. The Ornithocheiridae. Click to enlarge and expand.

We’ll start with Yixianopterus
Yixianopterus jingangshanensis JZMP-V12 (Lü et al. 2006) ~20 cm skull length, Barremian/Aptian Early Cretaceous ~125 mya, was overall 8x larger than and distinct from it tiny phylogenetic predecessor, Gmu-10157. The skull of Yixianopterus was longer judging by the pre-antorbital fenestra portion and the mandible. The teeth were more widely spaced. The caudals were shorter. Fingers 1-3 were smaller, but the wing finger was much more robust. Manual 4.1 approached the elbow when folded and the wingtip was higher than the skull when quadrupedal. The pelvis and tibia were more robust.

JZMP embryo

Figure 2. Click to enlarge DGS tracings. The JZMP ornithocheirid embryo, in situ and reconstructed.

We Haven’t Met the Adult Yet, But We Know This Embryo
The JZMP pterosaur embryo JZMP-03-03-2 (Ji et al. 2004) was found inside an eggshell, so we know it’s age precisely: zero. Considering the size of its pelvic opening one can estimate the size of the adult at 8x larger, which is consistent with Pterodaustro and its embryo/hatchling. The hypothetical adult size is also consistent with sister taxa. The embryo was originally compared to Beipiaopterus. Distinct from Yixianopterus, the skull of JZMP-03-03-2 was deeper anteriorly with an upturned premaxilla in which all of the premaxillary teeth were oriented chiefly anteriorly. The dentary was downturned at the tip. The antorbital fenestra was larger.The cervicals were longer posteriorly and shorter anteriorly. The sacrals were as long as the dorsals. The sternal complex was a wide rectangle with a transverse leading edge and a short cristospine. The scapula and coracoid were robust and oriented more laterally. The humerus was relatively smaller. The metacarpus was subequal to the ulna. The wing finger was robust proximally, but less so distally. Both m4.2 and m4.3 were longer than m4.1. The anterior ilium was much longer than the posterior process. The femur was shorter and the tibia was relatively longer. The pes was similar in size to that of Yixianopterus.

Note the long rostrum and small eye, as in the embryo of Pterodaustro. All of the small pedal bones were ossified. These facts falsify the hypothesis of pterosaur allometric growth (Wellnhofer 1970, Bennett 1991, 1992, 1994, 2001) and support the isometric hypothesis in which embryos and juveniles were almost identical to adults in morphology.

From Lebanon, a Nameless Pterosaur
The Lebanon ornithocheirid MSNM V 3881 (Dalla Vecchia, Adruini & Kellner 2001) A small, robust wing from Lebanon has a radius less than half the diameter of the ulna and manual digit 2 is subequal to 3. At present there is little else to distinguish it from Haopterus, except that it had a longer metacarpus relative to the ulna. The humerus, although incomplete, was small, as in the JZMP embryo.

The First Classic Ornithocheirid
Boreopterus cuiae JZMP 04-07-3 (Lü and Ji 2005) Distinct from the JZMP embryo, the skull of Boreopterus had at least 27 teeth in each upper jaw. They were long, slender and closely spaced. The rostrum was relatively longer and lower with a larger portion anterior to the antorbital fenestra. The postorbital portion was reduced with a posteriorly leaning orbit, as in Istiodactylus. The suborbital skull descended and the quadrate leaned posteriorly. The cervicals were longer with higher neural spines. The sacrals were shorter by more than half. The caudals were more robust. The humerus was larger, extending nearly to the acetabulum. The ulna and radius were also larger relative to the metacarpus. Fingers I-III were smaller. When folded the wing tip was no taller than the skull. The distal wing phalanges were shorter. The pelvis was tiny. The hind limb was more gracile, inluding a tiny foot.

Haopterus

Figure 3. Click to enlarge. Haopterus, the smallest ornithocheirid

Haopterus
Haopterus gracilis IVPP V11726 (Wang and Lü 2001) was overall smaller than and distinct from Boreopterus, the skull of Haopterus was shorter and relatively taller. The cervicals, dorsal, sacrals and caudals were all shorter. The scapula and coracoid were shorter. The humerus was extremely roubst with a deltopectoral crest extending for ~33% of the length. As in the Lebanon ornithocheirid, the radius and ulna were relatively short. Manual 4.1 approached the elbow. The relatively longer wing would have extended far above the head when folded. The pelvis was gracile and smaller. The femur was shorter. The metatarsals were shorter. Ornithocheirids, like Haopterus, were evidently spending more time in the air and less on the ground, judging by their wing/leg proportions.

Zhenyuanopterus

Figure 4. Click to enlarge. Zhenyuanopterus

Zhenyuanopterus
Zhenyuanopterus longirostris (Lü et alk. 2010) GLGMV 0001 Early Cretaceous. Distinct from Boreopterus, the skull of Zhenyuanopterus was longer, especially in the pre-antorobital fenestra region. The teeth were more widely spaced and continued erupting closer to the orbit, which was smaller. A squarish crest surmounted the mid rostrum. The cranium was crest-like, probably for muscle attachments. The cervicals were more robust. The torso was smaller and shallower, as in Haopterus. The caudals were more robust. The sternal complex did not have lateral ‘wings’. The scapula and coracoid were fused. The coracoids were laterally oriented. The humerus was as long as the torso. The ulna and radius were more robust and relatively shorter. The hind limbs were longer, as in Haopterus. The feet were extremely tiny with robust metatarsals and slender digits.

 

Arthurdactylus dorsal view.

Figure 5. Click to enlarge. Arthurdactylus dorsal view.

Arthurdactylus from South America
Arthurdactylus conandoylei 
(Frey and Martill 1994) SMNK 1132 PAL Early Cretaceous. Distinct from Zhenyuanopterus, the torso of Arthurdactylus was deeper, as in Boreopterus. The sacrals were all unfused. The caudals were vestigial. The coracoids were much longer than the scapula, producing a very high shoulder joint. The ulna was massive. Manual 4.1 approached the elbow when folded. The short pubis was directly beneath the actebulum. The ischium was slender. The foot was slightly larger than in Zhenyuanopterus with more slender metatarsals and longer digits.

In summary
Taxa at the base of the Ornithocheiridae are those closest to cycnorhamphids in their morphology. Yixianopterus is at the base followed by the JZMP embryo. Due to isometric growth in pterosaurs we can enlarge it eight times to gauge what the adult was like. A trend toward a longer snout, more and longer teeth, larger wings and smaller feet is apparent.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1994. Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153
Dalla Vecchia FM, Arduin P and Kellner AWA 2001. The first pterosaur from the Cenomanian (Late Cretaceous) Lagerstätten of Lebanon. Cretaceous Research 22: 219-225.
Frey E and Martill DM 1994. A new Pterosaur from the Crato Formation (Lower Cretaceous, Aptian) of Brazil. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 194: 379–412.
Ji Q, Ji S-A, Cheng Y-N, You HL, Lü J-C, Liu Y-Q and Yuan CX 2004. Pterosaur egg with leathery shell. Nature 432:572.
Lü J 2010. A new boreopterid pterodactyloid pterosaur from the Early Cretaceous Yixian Formation of Liaoning Province, northeastern China. Acta Geologica Sinica 24: 241–246.
Lü J and Ji Q 2005. A new ornithocheirid from the Early Cretaceous of Liaoning Province, China. Acta Geologica Sinica 79 (2): 157–163.
Lü J, Ji S, Yuan C, Gao Y, Sun Z and Ji Q 2006. New pterodactyloid pterosaur from the Lower Cretaceous Yixian Formation of Western Liaoning. In J. Lü, Y. Kobayashi, D. Huang, Y.-N. Lee (eds.), Papers from the 2005 Heyuan International Dinosaur Symposium. Geological Publishing House, Beijing 195-203.
Wang X and Lü J 2001. Discovery of a pterodactylid pterosaur from the Yixian Formation of western Liaoning, China. Chinese Science Bulletin 46(13):1-6.

Which Way Did Pterosaur Fingers Flex?

Pterosaur fossils have been known for over 200 years and yet we still argue about which way the fingers flexed. Undisturbed or minimally disturbed fossils give some clues. Fossil handprints do too.

Most pterosaur fossils are found crushed and the finger claws (unguals) are crushed along with the rest of the body (Figure 1). Tall and thin, like the raptorial, tree-clinging claws they were, pterosaur claws were most often preserved broad side down, tips pointing anteriorly, medial faces exposed. And that’s the way they are traditionally reconstructed, paying little attention to the cylinder-shaped interphalangeal joints or evolutionary precedent.

Right hand of Shenzhoupterus, dorsal view.

Figure 1. Click to enlarge. Right hand of Shenzhoupterus, dorsal view. Note the crushing of the ungual broadside down and disarticulation of the various finger joints. If you ignored these facts you might want to orient the claws anteriorly as shown.

There are Two Hypotheses at Work Here
In the traditional model (Bennett 2008) metacarpals 1-3 were stacked with #1 on top and all three were bound to metacarpal 4. See Figures 2 and 3. The fingers flexed anteriorly (in flight). Any specimens in which metacarpals 1-3 were found lined up anterior to metacarpal 4, Bennett (2008) ascribed to the effects of gravity on the bones after death.

Pterosaur hand dorsal view

Figure 2. Pterosaur hands, dorsal view, the two opposing hypotheses. See Figure 3 for anterior views to see how Bennett (2008) intended the fingers to stack with #1 on top. The Bennett configuration orients the fingers facing up when the hands are adducted (brought together), which would be unsuitable for tree climbing/clinging. The Peters configuration, like clapping hands, points the fingertips together, ideal for tree climbing.

In the heretical yet more conservative model (Peters 2002) metacarpals 1-3 lined up side-by-side anterior to metacarpal 4 and the fingers flexed ventrally (as in all other tetrapods). See Figures 2 and 3. In this configuration only metacarpal 4 twisted 90 degrees axially so the palmar side faced posteriorly (in flight) to facilitate wing folding. The three small fingers did not change their configuration or orientation. The palmar side of fingers 1-3 continued to point ventrally in flight.

Peters (2002) reported: “…in certain Cretaceous forms [the medial three digits] rotated into the vertical plane and became closely appressed to the much larger metacarpal IV (Bennett, 1991; 2000b). From this configuration, they flexed anteriorly in a subhorizontal plane when the wing was extended.” I apologize for this. Unfortunately I was influenced by Dr. Bennett at the time. Subsequent studies helped me realize the error of this statement.

Bennett and Peters pterosaur finger orientation configurations

Figure 3. Bennett (2008) and Peters (2002) pterosaur finger orientation configurations. See Figure 2 for dorsal views. Note: Bennett wanted digit 1 dorsal as shown here, not as in Figure 2.

The Wellnhofer (1991) Twist
Wellnhofer (1991) lined up the metacarpals anteriorly, but also twisted the unguals anteriorly. Of course, this could be a problem in pterosaurs with fingers of similar lengths and does not take into account the various disarticulations at several finger joints.

The Evolution of the Bennett (2008) Configuration
Bennett (2008) imagined the evolution of the pterosaur hand (Figure 4) based on an imaginary taxon. He started with the supination of the entire arm, which rotated all the palmar surfaces anteriorly. Metacarpal 4 became thicker than the others as it supported a lengthening wing finger. Overlooked by Bennett (2008), but implicit in his arguments, the next step involved migration of the metacarpals 1-3 as a unit down the anterior face of a much larger metacarpal 4. The supination of the hand envisioned by Bennett (2008) ultimately included reversing the flexion and extension of digit 4 such that hyperextension folded the wing in his view. No other tetrapod has ever done this. Also note there is no space for the large wing extensor between the attached metacarpals (1-3 back-to-front with 4) in the Bennett (2008) configuration. Bennett (2008) also envisioned the early disappearance of ungual 5 on the wing, which, due to supination, also faced anteriorly in this configuration. However, the wing ungual was retained. Bennett (2008) also imagined the loss of manual digit 5, but manual digit 5 was retained. He did not envision an origin for the preaxial carpal and pteroid, which occurred as far back as Cosesaurus (Peters 2009).

Pterosaur finger orientation in lateral view

Figure 4. Pterosaur finger orientation in lateral view, the two hypotheses. There are several problems with the Bennett (2008) hypothesis, least of all it leaves no room for the big wing extensor tendon.


The Evolution of the Peters (2002) Configuration
Peters (2002) discussed the evolution of his pterosaur hand configuration (Figure 4) based on actual taxa, including Longisquama insignis. Between Longisquama and the first pterosaur manual digit 4 was rotated axially so that the palmar (flexor) surface became the new posterior surface to facilitate wing folding in the plane of the wing with hyperflexion. Digit 5, already reduced, became a vestige. It revolved, along with metacarpal 4, to the new dorsal side of the metacarpus. During the rotation, metacarpals 1-3 shifted to the ventral rim of metacarpal 4 while retaining their configuration. This left plenty of room for a large extensor tendon (Figure 4). Contra Bennett (2008), flexion remained flexion in all the fingers. There was no reversal of function. The preaxial carpal and pteroid first appeared in the fenestrasaur and pterosaur precursor, Cosesaurus (Peters 2009) having migrated to the medial wrist from the central carpus where they were identified as the two centralia seen in Sphenodon.

Here’s Where the Trouble Started
In many crushed fossils, like  Shenzhoupterus (Figure 1) and the left hand of Eudimorphodon (Figure 5), the claws point anteriorly because they are crushed broadside down. In order to do this, some finger joints must disarticulate and this is always observable.

But look what happens in the right hand of Eudimorphodon
In the same Eudimorphodon (Figure 5) the right hand has the palmar surface exposed. The metacarpals were lifted and flipped over the palmar surface of metacarpal 4, but metacarpal 3 remained attached to metacarpal 4. Moreover the unguals pointed posteromedially. According to Bennett (2008) this should not have been possible if metacarpals 1-3 were bound to the anterior face of metacarpal 4 and pointed anteriorly. Digit 1 should have been buried first and deepest, but it was not.

Eudimorphodon hands.

Figure 5. Eudimorphodon hands. The right hand preserves the metacarpals lined up anteriorly with only metacarpal 3 attached to metacarpal 4. The claws are disarticulated due to crushing. The right hand, preserved with its palmar side exposed shows what happens when the lighter digits 1-3 drift as a unit with metacarpal 3 moving the least because it was attached to metacarpal 4.


Santanadactylus hand and fingers

Figure 6. Click to enlarge. Santanadactylus hand with metacarpals preserved at a 45 degree angle to the anterior face of metacarpal 4.

Even in 3D Fossils There Can be Some Confusion
Here, in this 3D Santanadactylus hand, the metacarpals have been raised like a drawbridge, far from their original orientation (palmar side down) and close to being pressed against the large metacarpal 4, palmar side anterior. Such a configuration permits no space for the big tendon between the appressed surfaces of metacarpal 4 and the three small metacarpals. This is an excellent example of taphonomic lifting on the hinge at the metacarpal 3-4 interface from an origin with the palmar side down for metacarpals 1-3. It is the only configuration that permits the big extensor tendon of metacarpal 4 to run unimpeded dorsal to the three small metacarpals and their extensor tendons (Figure 4). When the extensor tendon rots or pops, there is nothing to prevent metacarpals 1-3 from rising and falling like an airplane elevator in the drifting sea currents.

The left manus of Pteranodon KUVP 49400

Figure 7. The left manus of Pteranodon KUVP 49400 in a rare anterior burial. Here the unguals were crushed in their natural orientation, palmar side down. Thanks to M. Everhart at OceansofKansas.com for this image.

YPM 49400 – a Rare Anterior Burial and Posterior Exposure in Pteranodon
Here in a Pteranodon specimen YPM 49400 metacarpus was preserved anterior face down. This is a very rare burial. The manus was preserved intact and in its natural orientation, fingers 1-3 palmar side down and metacarpal 4 palmar (flexor) side now posterior for wing folding. The claws here pointed ventrally as in other tetrapods. The metacarpals lined up as in other tetrapods. Buried like this there was no chance for them to wave around or become disarticulated in the bottom currents. The proximal wing phalanx would have stood vertically erect (essentially the Z-axis) in this configuration, but it rotted, disarticulated and fell on its dorsum, exposing its ventral face.

Pteraichnus nipponensis

Figure 8. Pteraichnus nipponensis (Lee et al. 2009) along with a matching trackmaker, n23 of Wellnhofer 1970.

The Evidence of Ichnites
Pterosaur handprints (Figure 8) commonly preserve digits 1 and 2 laterally and digit 3 posteriorly. Sometimes digit 1 extends anteriorly (Lee et al. 2009). In the Bennett (2008) configuration, all three fingers would have extended posteriorly when quadrupedal because the arms were supinated. In the Peters (2002) configuration, all three fingers would have extended laterally when quadrupedal because the arms were neither supinated nor pronated, but in the neutral position.

Digit 3 Goes the Opposite Way
The key to orienting digit 3 posteriorly (and sometimes digit 1 anteriorly) goes back to the lizard ancestry of pterosaurs. The metacarpophalangeal joint of digit 3 is different than digit 2. Shaped more like a hemisphere than a cylinder, it permits digit orientation in several directions. With digit 3 directed posteriorly, digit 4 never touched the substrate. This evidence is in direct contrast with the configuration envisioned for the difficult to support wing launch hypothesis currently in favor also illustrated here.

On a Side Note
Bennett (2008) connects the extensor and flexors tendons to the proximal tips of the first wing phalanx. This is wrong. In lizards these tendons split in half, bypassing the nearest points and inserting further down the bone. As shown here, this permits complete wing folding, something the Bennett (2008) attachment is unable to do. We just learned about the evolution of the manus hand and pteroid from a Sphenodon-like ancestor here.

Bennett (2008) reported, “The reconstruction of the long extensor and flexor of thewingfinger suggests that there was no rotation of Mc IV about its long axis. If there had been a rotation, the tendon of m. flexor digiti quarti would have had to spiral posteriorly under the metacarpus to insert on the posterior process of wing phalanx 1 and the tendon of m. extensor digiti quarti longus to digit.” As mentioned above, it is a mistake to attach the flexor to the posterior process of wing phalanx 1, as Bennett (2008) proposes. Rather the insertion is further down the phalanx shaft, as in lizards, and in order to complete wing folding. Thus there would have been no problematic spiraling if metacarpal 4 rotated axially.

In Summary
All the evidence points to a configuration in which the hand of pterosaurs was configured the same as in all other tetrapods with the exception that the big wing finger was axially rotated so that the old palmar surface became the new posterior surface. This configuration is based on actual predecessor taxa, not figments of Bennett’s imagination. The new configuration creates a large channel for the massive extensor tendon that is missing from the Bennett configuration. The new configuration does not require the flexor side of the wing finger to become the extensor side and vice versa.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 2008. Morphological evolution of the wing of pterosaurs: myology and function. Zitteliana B28:127-141.
Lee YN, Azuma Y, Lee H-J, Shibata M, Lu J 2009. The first pterosaur trackways from Japan. Cretaceous Research 31, 263–267.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander Books, Limited, London, 192 pp.

The Pterosaur Pteroid …and Preaxial Carpal

Nyctosaurus pteroid

Figure 1. Nyctosaurus pteroid and preaxial carpal

The Bone(s) At the Center of the Argument
The pteroid and the preaxial carpal are two unique wrist bones not seen in other tetrapods, only pterosaurs (and their kin). The pteroid is longer, pointier and tends to bend around the anterior distal radius (Figure 1). The preaxial carpal (always getting second billing) is short, stout and provided with a sesamoid in a dorsal pit (Bennett 2007). Dr. David Hone’s (2008) post “That troublesome pteroid” reported, “Thanks to a lack of direct pterosaurian ancestors in the fossil record [ed. note: Hone refuses to accept fenestrasaurs as pterosaur precursors] we are not sure where the pteroid comes from…” Workers have argued over the pteroid’s homology, articulation and orientation. Here are some answers based on the fossil record (Figure 1).

What is a Pteroid?
Early workers, like Goldfuss (1831) considered the pteroid digit #1 and the wing finger digit #5. Williston (1911) dismissed that hypothesis and wondered if the pteroid were 1) a misplaced first metacarpal or centrale; 2) a bone derived from sinew (tendon) or 3) an elongated sesamoid. Unwin et al. (1996) determined that the pteroid was a true bone, but could not determine its homology. Peters (2002) reported that the pteroid and preaxial carpal were homologs to centralia 1 and 2 of Romer (1956) because pterosaurs do not have centralia in their primitive positions. Peters (2009) found a tiny pteroid and preaxial carpal in Cosesaurus a phylogenetic precursor to pterosaurs. Here the pteroid and preaxial carpal are homologous with the centralia of Sphenodon, a taxon that shares a common ancestor with pterosaurs at the base of the Lepidosauria. Their migration of the centralia to the medial rim of the wrist is discussed below (Figure 2).

Figure 2. Click to enlarge. The origin of the pterosaur wing and the migration of the pteroid and preaxial carpal. A. Sphenodon. B. Huehuecuetzpalli. C. Cosesaurus. D. Sharovipteryx. E. Longisquama. F-H. The Milan specimen MPUM 6009, a basal pterosaur.

Pteroid Articulation
Early hypotheses placed the base of the pteroid in the dorsal pit of the preaxial carpal (Marsh 1882, Hankin and Waton 1914, Frey and Riess 1981, Padian 1984, Wilkinson et al. 2006). Bennett (2007) pointed out that the cup was preoccupied by a sesamoid and indicated that the pteroid articulated to the side of the preaxial carpal in a minor depression. Peters (2009) pointed out that Bennett’s (2007) own data demonstrated that the base of the pteroid actually articulated with the saddle-shaped joint on the proximal syncarpal (radiale) and only weakly contacted the proximal medial surface of the preaxial carpal.

Which Way Did the Pteroid Point?
Concerning its relative position some authors have postulated an anteriorly facing pteroid able to rotate to a variety of postions based on the suggested higher aerodynamic efficiency of a larger propatagium (Frey and Riess 1981; Wilkinson et al. 2006) and able to swivel while inserted within the preaxial cup. Both are wrong. All articulated pteroids face medially (Bennett 2007) on the anterior face of the radiale (proximal syncarpal, Peters 2009). The pteroid was a passive element, as are all carpals, moving only slightly as the propatagium was tightened or relaxed (Figure 6).

Carpus of Sphenodon

Figure 3. Click to Enlarge. Carpus of Sphenodon comparing the medial and lateral centralia to the pteroid (yellow) and preaxial carpal (blue) of pterosaurs.

How Did the Pteroid Come to Be?
A pterosaur precursor, Cosesaurus, also has a tiny pteroid, a preaxial carpal and its attendant sesamoid (Peters 2009), indicating a nonvolant origin for this unusual carpal configuration. Subsequent study has shown that Sharovipteryx and Longisquama also have a pteroid and preaxial carpal. Fenestrasaurs and all tritosaurs following Lacertulus and Huehuecuetzpalli lack centralia.

More primitive tetrapods, like Sphenodon, have centralia the same shapes as the pteroid and preaxial carpal in fenestrasaurs (Figure 3). The medial centrale in Sphenodon is long and pointed medially. The lateral centrale is short and stout. Neither are insertion or origin points for any muscles or tendons. They are only spacers, keeping the distal carpals apart from the proximal carpals. After migration in tritosaurs the distal carpals articulated with the proximal carpals. The intermedium and pisiform disappeared during the process, probably by fusion and reduction respectively.

Wing evolution in pterosaurs

Figure 4. Wing evolution in pterosaurs. Click to enlarge and animate.

Considering their original and ultimate orientation, the medial carpal likely emerged first, turned the corner, and was followed by the lateral carpal, which moved distally to the anterior face of the first distal carpal. Relieved of the intervening centralia, the distal carpals articulated with the proximal carpals as they do in pterosaurs. The migration time appears to be at the Lacertulus Huehuecuetzpalli stage in which the entire carpus was poorly ossified.

Why Did The Pteroid and Preaxial Carpal Migrate?
At the Lacertulus / Huehuecuetzpalli stage the ancestors of pterosaurs were practicing bipedal locomotion (Carroll and Thompson 1982, Peters 2000) in a manner similar to living lizards capable of bipedal locomotion (Snyder 1954). Peters (2000) provided ample evidence for this. In addition, between Huehuecuetzpalli and Cosesaurus the coracoid fenestrations expanded leaving only the posterior rim as a strut. That meant the former sliding coracoid disc upon the interclavicle and clavicle was reduced to an immovable stem inserted into a cup, as in pterosaurs and birds. Since pterosaurs and birds flap their forelimbs, we can imagine that Cosesaurus, provided with the same type of coracoid, did so as well. Cosesaurus also developed precursor wing membranes in the form of trailing aktinofibrils (Peters 2009), which supports the flapping hypothesis. Since the pteroid was intimately associated with the propatagium in pterosaurs, it is safe to assume that some sort of minor propatagium was present in Cosesaurus, too (Figure 6). A propatagium is a passive restraint on elbow overextension and increases the wing area. Perhaps Cosesaurus gained stability and thrust from flapping while running with these new dermal extensions. Or perhaps these were secondary sexual traits, or both!

Evidence from Fenestrasaur Manus Tracks
The manus tracks pointed directly anteriorly in Rotodactylus and other lepidosaurs, while in pterosaurs they pointed laterally. By this evidence, Cosesaurus, a likely trackmaker of Rotodactylus and a pterosaur precursor, was still able to pronate its forarms. Pterosaurs could not. The loss of the intermedium and the straightening of the radius and ulna reduced the ability of the forearm to suppinate and pronate in pterosaurs (contra Bennett 2008). This continued straightening and lack of pronation was a product of bipedal locomotion together with flight restraints. For the same reasons neither bats nor birds can pronate or supinate their forearms.

Rotodactylus tracks

Figure 5. Click to enlarge. Rotodactylus tracks. These digitigrade tracks match to Cosesaurus (Peters 2000). Digit 5 is posterior to the other four digits in both the manus and pes. The hands imprinted very close to the center line of the track.

How Did the Centralia Migrate?
The two centralia of Sphenodon, were neatly and inconspicuously tucked in at the same level with the rest of the carpals. When they migrated to a medial position on the wrist both were elevated above the traditional wrist contours, acting like twin violin bridges to pull the extensor tendon taut whenever the elbow was extended for flight. Originally the centralia were not insertion points for any muscles or tendons. Rather all the hand muscles and tendons passed over them and at right angles to their long axis (Figure 3).  In pterosaurs the extensor tendons pass over the pteroid parallel to the long axis.

The migration of the centralia occurred when the carpus was poorly ossified. The centralia migrated little by little, generation after generation, while the manus was elevated in a bipedal configuration and while it was not being used for traditional quadrupedal lizard-like locomotion. In living lizards capable of bipedal locomotion, the hands do nothing. That was likely the case in the Late Permian/Early Triassic prior to the appearance of Cosesaurus. By then the hands were flapping, based on the morphology of the Cosesaurus coracoid (see above).

The Propatagium and Overextension of the Elbow
It is a common mistake in reconstructing pterosaur wings to overextend the elbow and extend the propatagium to the neck (Frey et al. 2006; Bennett 2007,  2008; Prondvai and Hone 2009). Bats and birds rarely extend the elbow more than 20 degrees beyond a right angle and pterosaurs would have been the same (Peters 2002). All available evidence indicates that the propatagium stretched between the pteroid and deltopectoral crest, not the neck.

Bennett’s (2008) Incorrect Reconstruction
Bennett (2008) proposed a strange reconstruction of pterosaur wing myology (musculature) by reversing the extensors and flexors. He reported, “…the range of motion of the metacarpophalangeal joint of digit IV migrated posteriorly so that flexor muscles spread the wing and extensor muscles folded it.” Bennett (2008, fig. 3) insisted that the pterosaur forearm was suppinated (radius over ulna in dorsal view) but illustrated the wing in the neutral position (radius anterior). His reconstruction failed to inserte and originate no muscles or tendosns on the dorsal or palmar sides of the distal carpus, and only two minor slips on the proximal carpus, contrary to the pattern of all other tetrapods.

Prondvai and Hone’s (2009) Big Hypothetical Tendon
Prondvai and Hone (2009) attempted to model a hypothetical biomechanical automatism to keep the wings open in flight in order to save energy, as in bats and birds. They proposed a propatagial ligament or ligamentous system which, as a result of the elbow extension, automatically performed and maintained the extension of the wing finger during flight and prohibited the hyperextension of the elbow. Unfortunately they overextended the elbow in their pterosaur and bat reconstructions, they avoided involving the pteroid in their ligament and they offered no evolutionary pathway to produce their hypothetical ligament. Instead, their imagined ligament ran like a rope through the middle of the propatagium. Nothing like this has ever been recovered in the soft tissue fossil record. Actually the biomechanical automatism was the entire propatagium, a likely homolog to the m. extensor digitorum longus of lizards and Sphenodon.

Sphenodon hand muscles

Figure 6. Sphenodon hand muscles

Extensor Muscles and Tendons
In lepidosaurus, such as Sphenodon (Haines 1939) and Polychrus (Moro and Abdala 2004), the m. extensor digitorum longus originates on the distal humerus, splits four ways distally and inserts on the proximolateral side of metacarpals 1-4, passing over both centralia (Figure 6). M. extensor digitorum longus does not extend to the base of the first phalanx as Bennett (2008) proposed and Prondvai and Hone (2009) supported in Sphenodon, but it may have done so in pterosaurs to facilitate automatic wing extension with elbow extension Figure 7). The short digital extensors of digits 1-3 originate on the intermedium (in Sphenodon) and insert on the distal metacarpals of digits 1-3 with a tendon extending to the ungual. They short extensors also pass over the lateral centrale. The short digital extensors of digit IV originate on the ulnare and distal ulna. The short digital extensor of digit 5 originates on the ulnare and pisiform.

Figure 7. Pterosaur wing flexed and extended, compared to Cosesaurus and demonstrating the hypothetical movement of the loosely articulated pteroid and preaxial carpal.

In fenestrasaurs, including pterosaurs, the intermedium fused to the radiale which served to straighten out the extensors of digits 1-3 in line with metacarpals 1-3. If the long extensor from the humerus did not send a slip to the wing finger, then the extensor digitorum brevis of digit 4 that originated on the distal ulna extended the wing finger. This tiny muscle seems unworthy due to the mass, moment and drag the giant wing finger would exert on it. Rather the expanded long extensor, now called the propatagium likely pulled the pteroid during elbow extension. The pteroid, in turn, pulled the wing finger open.

Sesamoids
Sesamoids are defined as skeletal elements that develop within a continuous band of regular dense connective tissue (tendon or ligament) adjacent to an articulation or joint (Jerez et al. 2009). Lepidosaurs don’t have sesamoids on their centralia. They would have developed on the preaxial carpal at the point of stress.

In summary
According to the evidence, the pteroid and preaxial carpal were former centralia that had migrated to the medial wrist during early experiments with a bipedal configuration. The pteroid pointed medially and was a passive bone, unable to change its orientation except within the confines of a stretched or relaxed propatagium. During elbow extension, the propatagium pulled the pteroid medially, which extended the wing finger via a new set of tendons not seen in Sphenodon because its centralia were not involved in any tendons or muscles.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 2007. Articulation and Function of the Pteroid Bone of Pterosaurs. Journal of Vertebrate Paleontology 27(4):881–891.
Bennett SC 2008. Morphological evolution of the wing of pterosaurs: myology and function. Zitteliana B 28 127-141.
Carroll and Thompson 1982. A bipedal lizardlike reptile fro the Karroo. Journal of Palaeontology 56:1-10.
Frey E and Riess J 1981. A new reconstruction of the pterosaur wing.Neues Jahrbuch für Geologie und Paläontologie Abhandlungen 161:1–27.
Goldfuss GA 1831. Beiträge zur Kenntnis verschiedener Reptilien der Vorwelt. Nova acta Academiae Caesareae Leopoldino−Carolinae Germanicae Naturae Curiosorum 15: 61–128.
Haines RW 1939. A revision of the extensor muscles of the forearm in tetrapods. Journal of Anatomy 80(1):211-233.
Hankin EH and Watson DSM 1914. On the flight of pterodactyls. The Aeronautical Journal 18: 324–335.
Jerez A, Mangione S and Abdala V 2009. Occurrence and distribution of sesamoid bones in squamates: a comparative approach. Acta Zoologica (Stockholm) doi: 10.1111/j.1463-6395.2009.00408.x
Marsh OC 1882. The wings of pterodactyles. American Journal of Science, 23, 251-256.
Moro S and Abdala V 2004. Análisis descrptivo de la miología flexora y extensora del miembro anterior de Polychrus acutirostris (Squamata, Polychrotidae). Papéis Avulsos de Zoologia 44(5):81-89.
Padian K 1983.
Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yeal Peabody Museum. Postilla, 189.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. 
A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Prondvai E and Hone DWE 2009. New models for the wing extension in pterosaurs’,Historical Biology 20 (4):237-254.
Snyder RC 1954. The anatomy and function of the pelvic girdle and hind limb in lizard locomotion. American Journal of Anatomy 95:1-46.
Unwin DM, Frey E, Martill DM, Clarke JB and Riess J 1996. On the nature of the pteroid in pterosaurs. Proceedings of the Royal Society of London B 263:45–52.
Wilkinson MT, Unwin DM and  Ellington CP 2006. High lift function of the pteroid bone and forewing of pterosaurs. Proceedings of the Royal Society of London B 273:119–126.

The Family Tree of the Pterosauria 16 – The Cycnorhamphidae

Earlier we looked at the descendents of Scaphognathus that shrank through Ornithocephalus to begat Pterodactylus. Then, we followed another shrinkage through No. 6 that begat Germanodactylus. Two germanodactylids were basal to lineages that ultimately produced Tupuxuara and Pteranodon among others.

Pterosaur family tree

Figure 3. Click to enlarge. The pterosaur family tree.

Here we back up to Scaphognathus to retrieve the last branch of the Pterosauria, the one leading to Cycnorhamphus and the ornithocheirids culminating with Anhanguera and a host of others.

Cycnorhamphus, its sisters and predecessor taxa

Figure 1. Cycnorhamphus, its sisters and predecessor taxa

Start Small and Get Smaller
We begin this clade with a small Scaphognathus, the Maxberg specimen, No. 110 in the Wellnhofer (1975) catalog. It was originally considered a juvenile because it stood only as high as the hips of the holotype, No. 109 and it appeared to have the expected juvenile proportions. Actually it was a small adult as we learned earlier. Distinct from SMNS 59395 the skull of the Maxberg specimen had a relatively shorter, blunter skull and larger orbit. The teeth were more robust. The postorbital process of the jugal was vertical. The premaxillary teeth are not so reduced. The quadratojugal process of the jugal is reduced to a nub. The mandible appears to shallow posteriorly. The cervicals were shorter, half the torso length. The tail was shorter and more gracile. Extended hemal arches and zygopophyses are present, but extremely gracile. The sternal complex was more circular. The humerus was greatly reduced. The ulna and radius were shorter. Manual digits II and III were subequal. The wing was slightly shorter. The ischium was broader, higher and smaller. The small foot was just longer than half the tibia. Metatarsal I was longer than mt II. Pedal 5.1 extended nearly to the ungual of digit IV.

TM13104
TM 13104 (Winkler 1870, No. 34 in the Wellnhoger 1970 catalog) was considered a juvenile Pterodactylus, but it is unrelated. Distinct from ScaphognathusNo. 110, the skull of No. 34 was shorter with a larger orbit. Following a shallow premaxilla, the naris was still separate from the antorbital fenestra The medial premaxillary teeth were oriented anteriorly. The rostral teeth were the same size and tiny. Extended hemal arches and zygopophyses were absent, but the caudals were more robust. The sternal complex shield was anteroposteriorly shorter with lateral processes enlarged. The scapula was subequal to the coracoid. The metacarpus was greatly elongated and subequal to the ulna. The proximal wing elements were longer such that the joint between m4.2 and m4.3 was beyond the elbow. The ischium was broad and its rims approach both the pubis and ilium. Metatarsal V was shorter. The metatarsals were not appressed.

Gmu-10157
Gmu-10157 (undescribed) was considered a juvenile Pterodactylus, but it is unrelated. Distinct from No. 34, the skull of Gmu-10157 had a longer skull and deeper premaxilla, as in Scaphognathus, No. 110. The antorbital fenestra was elongated anteriorly and the naris was greatlty reduced to the size of the secondary naris. The teeth were larger than in No. 34 and smaller than in No. 110. The postorbital was raised to the top of the orbit. The cervicals were elongated. The humerus was more elongated and robust. Fingers I-III were longer. The prepubis was broader. The ischium was smaller. The tibia was more robust. Pedal digit V was longer.

Relatively Gigantic Yixianopterus is Where Cycnorhamphids and Ornithocheirds Part Company
Yixianopterus jingangshanensis JZMP V-12 (Lü et al. 2006) ~20 cm skull length, Barremian/Aptian Early Cretaceous ~125 mya, was considered an ornithocheirid pterosaur like Haopterus, but it also nests at the base of the Cycnorhamphidae. Overall much larger than and distinct from Gmu-10157, the skull of Yixianopterus was probably longer judging by the pre-antorbital fenestra portion and the mandible. The teeth were more widely spaced. The caudals were shorter. Fingers I-III were smaller, but the wing finger was much more robust. Manual 4.1 approached the elbow when folded and the wingtip was higher than the skull when quadrupedal. The pelvis and tibia were more robust.

Then (Perhaps) Another Size Decrease with BSp 1968 XV 132
Distinct from Yixianopterus, the skull of BSp 1968 XV 132 was longer and lower with more and smaller teeth. The mandible was similarly gracile. The cervicals were longer with tall neural spines. The torso was relatively smaller and shallower. The pectoral girdle was smaller. The humerus was longer and the entire wing was more gracile. Manual 4.1 extended only to the mid ulna. Fingers 1-3 were even smaller. The ilium was more gracile with a greatly reduced posterior process. The tibia was longer and more gracile. The pes was relatively smaller.

And Another Size Decrease with No. 30
B St 1936 I 50 (no. 30 in the Wellnhofer 1970 catalog) ~2.5 cm skull length, Late Jurassic ~150 mya. Standing ~7 cm tall, this is one of the smallest of all known pterosaurs. If it was an adult, eggs were no more than 3 mm in diameter. Much smaller than and distinct from BSp 1968 XV 132, the skull of no. 30 was relatively smaller with a shorter rostrum. The cervicals had short neural spines. The torso was longer. The sternal complex was wider. The coracoid was longer. The humerus was longer and more robust. The wing finger was more gracile. The pubis was directed ventrally. The prepubis had a large perforation. The feet were larger and digit V was especially enlarged.

A Size Increase with Cycnorhamphus
Cycnorhamphus suevicus GPIT specimen (Pterodactylus suevicus Quenstedt 1855, Cycnorhamphus suevicus Seeley 1870, no. 53 in the Wellnhofer 1970 catalog) Kimmeridgian, Late Jurassic ~150mya, ~1.3 meter wingspan, was considered species of Pterodactylus, then a ctenochasmatid. Overall much larger than and distinct from No. 30, the skull of Cycnorhamphus was more robust with a large parietal crest with a narrow frontal contribution. The anterior maxilla was slightly upturned. The teeth were longer in the anterior portion of the jaws. The eighth cervical was reduced. The torso was shorter (more compact) with a larger porportion devoted to the sacrals. The sternal complex was rounder, lacking any of the sharp corners found in No. 30. The scapula was shorter and more laterally oriented. The humerus was shorter, but the elbow still extended posteriorly just to the tip of the ilium. The metacarpals were longer as were fingers I-III. Digit III was an ungual longer than II. The pelvis was more robust. The tibia was longer in concert with the metacarpus such that the wrist and knee remained aligned. Pedal digits II and V were further elongated.

A Slightly Larger Cycnorhamphus
Formerly Gallodactylus, C.  canjuersensis MNHN CNJ 71 (Fabre 1974, 1976; Bennett 1996) is about 40 per cent larger overall, had a shorter wing (not higher than the skull when folded) and a distinct coracoid and pelvis shape. The “prefrontal” of Fabré (1974, 1976) appears to be a lacrimal. The “quadrate” appears to be metacarpal 3 due to its rod-like shape, expanded distal articular surface and proximity to mc IV. The “pterygoid” appears to be the ectopalatine. The “right jugal” appears to be a quadrate due to its angle, position and simple broad shape. The “left corocoid” is a short scapula and the attached “humerus (H.d)” is a coracoid, as Bennett noted. The other “humerus (H.g)” is only half the relative size of the humerus in C. suevicus, so it appears to be another attached scapula.

Another Even Larger Cycnorhampus
A much larger private specimen known only from a skull and jaw with a peculiar vomer expanded into a half disc that fit into a bent mandible can be attributed to Cycnorhamphus, but it is a distinct species.

Feilongus
Feilongus youngi (Wang, Kellner, Zhou and Campos, 2005)~30 cm skull length, Barremian-Aptian, Lower Cretaceous ~125 mya, was considered a ctenochasmatid and an ornithocheirid. Larger overall and distinct from Cycnorhamphus, the skull of Feilongus had a rostrum twice as long. The dorsal margin of the skull was concave from tip to tip. More teeth that were more widely spaced lined the anterior jaws. The anterior rostrum was spoon-shaped.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 2010. The Morphology and Taxonomy of Cycnorhamphus. Acta Geoscientica Sinica 31 Supplement 1, The Flugsaurier Third International Symposium on Pterosaurs.
Lü J, Ji S, Yuan C, Gao Y, Sun Z and Ji Q 2006. New pterodactyloid pterosaur from the Lower Cretaceous Yixian Formation of Western Liaoning. In J. Lü, Y. Kobayashi, D. Huang, Y.-N. Lee (eds.), Papers from the 2005 Heyuan International Dinosaur Symposium. Geological Publishing House, Beijing 195-203.
Wellnhofer P 1975a. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33.1975b. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. 1975c. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.

The Family Tree of the Pterosauria 15 – Pteranodon

We just looked at the base of the Protopteranodontia and Nyctosaurus. Today we’ll finish up the Pteranodontia with everyone’s favorite, Pteranodon, then later move over to the Cycnorhamphus/Ornithocheirid clade.

Pteranodon skulls

Figure 1. Click to enlarge. A family tree of Nyctosaurus and Pteranodon. Note the gradual size increase followed by, in one lineage, a size decrease.

No one has contributed more to our understanding – and misunderstanding – of Pteranodon (Marsh 1876) more than Dr. S. Chris Bennett. His detailed and unprecedented 1991 PhD thesis on Pteranodon was subsequently split into several published papers (Bennett 1992, 1993, 1994) culminating with a reprinting of his PhD thesis in two parts (2001). Bennett’s hypotheses on pterosaur juveniles, growth, bone fusion and family trees have been the basis for many current studies. Unfortunately, his use of statistics, rather than phylogenetic analysis and his reliance on the outdated archosaur paradigm, rather than the new lizard model, has created problems  in his assessments of growth patterns, gender and speciation in Pteranodon and other taxa.

Two species or several?
Bennett (1991, 1992,  1993, 1994, 2001) reduced Pteranodon to two species: the holotype P. longiceps and the high-crested P. sternbergi. All other variations (Figure 1) Bennett ascribed to gender and immaturity. Phylogenetic analysis tells a different story. I analyzed the specimens above (Figure 1) and found a huge variety that nested in a phylogenetic sequence. Smaller taxa generally were more primitive (but the exceptions (R-V and Z4 in Figure 1) tell another story, see below).  P. occidentalis YPM 1179 (Marsh 1876) is the one closest to the outgroup, the private specimen of Germanodactylus, SMNK PAL 6592. Here a gradual increase in size and crest size, among many other traits is documented followed by a size decrease in a clade descending form a sister to P. ingens.

The Triebold specimen and UALVP 24238, the two most complete Pteranodon known

Figure 2. Click to enlarge. The Triebold specimen and UALVP 24238, the two most complete Pteranodon known. These two are nearly sister taxa and still the morphological variation is striking.

Kellner assigned some Pteranodon specimens to new genera
Kellner (2010) reassigned the Alberta specimen, UALVP 24238, (Z in Figure1) to a new genus and species: Dawndraco kanzai because the upper and lower margins of the rostrum were nearly parallel to one another, rather than tapering, as in all other specimens. Bennett (1991, 1994, 2001) had a assigned it to P. sternbergi. Here the Alberta specimen was derived from USNM 12167 (W in Figure 1) and is at the base of a clade of two other tall but slender crested Pteranodon specimens, AMNH 5099 and YPM 2473 (Z2 and Z3 in figure 1), both of which lack a rostrum for comparison. So a new genus does not appear warranted, only a new species: Pteranodon kanzai. Kellner (2010) also reassigned Pteranodon sternbergi FHSM VP 339 (Harksen 1966) to a genus previously erected by Miller (1972), Geosternbergia sternbergi. Again, considering the wide variation in species within several other widely recognized pterosaur genera (Rhamphorhynchus, Pterodactylus, Campylognathoides, Dorygnathus, etc.), such an assignment appears to be unwarranted until all these other genera are similarly split apart. Actually there is greater morphological disparity in several other Pteranodon specimens, but this was overlooked.

Gradual Increase in Size Followed by Gradual Decrease
We’ve already seen what happens in various other pterosaur clades as size increase is followed by decrease and followed again by increase. We see the same pattern in Pteranodon. Phylogenetically the largest specimens in the P. ingens clade were followed by smaller specimens. Of greater interest, these specimens had a shorter rostrum and an unfused scapulocoracoid, a pattern seen in other pterosaurs lines. Bennett (1991) and others ascribed a short rostrum and lack of fusion to immaturity (following the archosaur model). But that is false. Pterosaurs were lizards with lizard-like growth patterns. In living lepidosaurs, Maisano (2002) reported, “no terminal fusion universally coincides with the achievement of either sexually or skeletally mature size and that some squamates continue to grow long after the fusion of various elements.” Thus pterosaurs, as squamates, could have fused bones early in ontogeny. They could also have never fused certain bones before they died of old age. Under the squamate paradigm, “immature” bone texture could have been retained in phylogenetically smaller adults. This is a key fact that has been previously overlooked or ignored by Bennett and others. And that’s why you only find unfused scapulocoracoids in these smaller derived taxa (R, S, T and Z4 in Figure 1), not in the more primitive taxa (L – N ) of similar size.

Post-crania Pteranodon

Figure 3. Click to enlarge and identify. Various Pteranodon specimens known from post-crania. Note the yellow box includes one of the largest specimens, but it has an unfused extensor tendon process, which may mean it is a very large Nyctosaurus with fingers, following the pattern in primitive Nyctosaurus.

Over 1000 Specimens, Few Even Close to Complete.
Unfortunately, most Pteranodon corpses did not stay intact on their way to the sea floor. That makes it more of a puzzle with smaller pieces to work with. Very few skulls are associated with post-crania. Skull-only and skull-less taxa are the rule. Can they be correlated? The answer is yes, at least somewhat. Fortunately we know more about the P. sternbergia clade because we have two relatively complete specimens from that clade (Figure 2). When we employ skull and skull-less taxa together we get much less phylogenetic resolution because there are no traits certain sisters have in common. However if we run two analyses, one with skulls and one without, then we don’t have that problem. What we get our two very similarly split trees that enable us to match certain post-crania with skulls by the process of elimination and phylogenetic analysis (Figure 4).

Comparing Pteranodon Skull and Skull-less taxa

Figure 4. Click to enlarge. Comparing Pteranodon skull and skull-less taxa. The three main clades (basal, P. ingens and P. sternbergi) are recovered either way.

What We Can Learn from a Juvenile Pteranodon
Several years ago, a juvenile Pteranodon (informally known as “Ptweety”, Figure 3C) was found and (unfortunately) mounted with lots of putty into a standing reconstruction and sold to a retailer. These actions removed this specimen from the possibility of appropriate academic study. Even so, I was able to see photographs of the in situ specimen, examine casts and talk with the preparator. Ptweey was one-quarter as tall as the largest known pterosaur, P. ingens and had adult proportions (long rostrum, small orbit, wing elements proportional, etc.). That means it would have been twice as tall as a standing hatchling. As in all Pteranodon, the extensor tendon process was fused to manual 4.1.

Lack of Fusion Means Immaturity?
Bennett (1991, etc.) reported on a very large proximal wing phalanx (Figure 3o) without a fused extensor tendon process (YPM 2501), but this specimen belongs to a very large Nyctosaurus.

Female Pteranodon?
Bennett (1991, 1992, 2001) reported on a disassociated pelvis that he believed belonged to a female Pteranodon because it had a deeper pelvic opening than all other Pteranodon pelves, including the Triebold specimen, which has a small crest (which meant it should have also been female). The only problem is, the pelvis in question, KUVP 993, is identical to smaller Nyctosaurus pelves (Figure 5). Here is yet another clue that a big Nyctosaurus roamed the airspace over the Niobrara Sea.

Female Pteranodon?

Figure 5. Pteranodon and Nyctosaurus pelves in left lateral view. A. Pteranodon ingens YPM 1175, reconstructed from Eaton (1910). B. Pteranodon sp. UNSM 50036. C. The TRIEBOLD specimen of Pteranodon, NMC 41-358, tracing from in situ specimen. D. Pteranodon sp. UALVP 24238, tracing from in situ specimen. E. Nyctosaurus bonneri, FHSM VP 21 reconstructed. F. Nyctosaurus gracilis, FMNH 25026 in situ G. Nyctosaurus sp. UNSM 93000, reconstructed. H. The same enlarged 1.85x to reflect the hypothetical pelvis size of the largest known Nyctosaurus (Bennett 2000). I. Dubious Pteranodon? KUVP 993 tracing from extricated specimen and slightly reconstructed. While larger than any other known Nyctosaurus pelvis, KUVP 993 has a pelvic aperture deeper than any Pteranodon (Fig. 3a) and morphologically more similar to Nyctosaurus specimens. The obturator foramen rivals and surpasses the acetabulum diameter in Nyctosaurus, not Pteranodon. Thus KUVP 993 does not represent a female Pteranodon pelvis, but a very large Nyctosaurus pelvis. Scale bar = 10 cm. Black circles are approximate egg diameters able to pass through each pelvic opening. Note C and D are associated with skulls (Fig. 2) in the P. sternbergi lineage.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1993. The ontogeny of Pteranodon and other pterosaurs. Paleobiology, 19:92-106.
Bennett SC 1994. Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153.
Eaton GF 1910. Osteology of Pteranodon. Memoirs of the Connectictut Academy of Arts and Sciences 2:1-38.
Harksen JC 1966. Pteranodon sternbergi, a new fossil pterodactyl from the Niobara Cretaceous of Kansas. – Proceedings of the South Dakota Academy of Science 45: 74–77.
Kellner AWA 2010. Comments on the Pteranodontidae (Pterosauria, Pterodactyloidea) with the description of two new species. Anais da Academia Brasileira de Ciências 82(4): 1063-1084.
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrate Paleontology 22:268-275.
Marsh OC 1876. Notice of a new sub-order of Pterosauria. American Journal of Science, Series 3, 11:507-509.
Miller HW 1972. The taxonomy of the Pteranodon species from Kansas. Transactions of the Kansas Academy of Science 74: 1–19.

The Family Tree of the Pterosauria 14 – Nyctosaurus

Earlier we looked at the base of the Protopteranodontia, a clade that originated with a private specimen incorrectly referred to Germanodactylus cristatus. The clade also included No. 13, Eopteranodon and Eoazhdarcho and the Pteranodontia (Nyctosaurus + Pteranodon).

Here we look at Muzquizopteryx and the variety within the genus Nyctosaurus.

Nyctosaurus clade

Figure 1. The clade of Nyctosaurus and kin. Click to enlarge.

Muzquizopteryx
At the base of the genus Nyctosaurus is the smallest, newest and most primitive member of the nyctosaur clade, Muzquizopteryx (Frey et al. 2006). Overall larger than and distinct from No. 13, the skull of Muzquizopteryx had a longer rostrum, a shorter antorbital fenestra. The crest was shorter. The orbit was smaller, the lateral temporal fenestra was larger. The cervicals were more robust and shorter with higher neural spines. The cristospine was longer, The scapula was no longer than the coracoid. The deltopectoral crest was expanded distally. The pteroid was right angled. Fingers 1-3 were larger.The ischium was narrower. The prepubis fenestra was expanded beyond the anterior rim creating an anterior and ventral process. The femur and tibia were shorter. The foot was larger with longer toes. Pedal digit 5 was a vestige. It is not know whether Muzquizopteryx had jaw rim teeth or not.

Nyctosaurus bonneri, the Fort Hays specimen
Nyctosaurus bonneri FHSM VP 2148 (Bonner 1964, Miller 1972) Coniacian, Late Cretaceous was Overall larger than and distinct from Muzquizopteryx, the skull of Nyctosaurus bonneri was downturned anterior to the antorbital fenestra. No crest was present. The postorbital process of the jugal was gracile. The mandible was nearly as deep as the skull. No jaw rim teeth were present. The cervicals were shorter and more robust. The sacrum was coosified. The sternal complex was shorter and wider. The scapula and coracoid were more robust. The deltopectoral crest was greatly enlarged. The metacarpus was elongated. Fingers 1-3 were vestiges, probably because they could not touch the ground. Compared to Eopteranodon, the wing was longer. The distal wing phalanges were relatively longer. The pelvis was relatively smaller. The hind limb and foot were relatively shorter. The increase in wing length and decrease in leg length means this Nyctosaurus probably spent more time flying. The short crest sometimes applied to this specimen is an artifact made of putty.

YPM 2501
Size-wise and according to Bennett (1991, 2001) YPM 2501 is a Pteranodon distal metacarpus and proximal portion of the manual 4.1 (the wing finger). The strange thing is, this specimen is larger than virtually all — if not all — known specimens of Pteranodon — AND — the extensor tendon process is not fused. This specimen is a problem for Bennett (1991, 2001) and most other current pterosaur workers because an unfused extensor tendon process, to them, means an immature specimen (following archosaur growth pattern traits). However, following lizard growth patterns and phylogenic patterns this is probably a Nyctosaurus, because Pteranodon fuse the ETP. Crestless nyctosaurs don’t. This specimen also had larger fingers than later, more derived taxa.

Nyctosaurus nanus
The smallest Nyctosaurus (about the size of Muzquizopteryx) is N. nanus, known only for a humerus and pectoral girdle.

Nyctosaurus gracilis, the Field museum (Chicago) specimen
Distinct from the N. bonneri, the skull of N. gracilis (Williston 1902a, b) FMNH 25026 had a slightly deeper rostral tip and a straighter dorsal margin without the posterior downturn, as in Muzquizopteryx. The mandible was probably thinner, but it is crushed dorsoventrally. The cervicals were slightly smaller. The sacrals were relatively larger. The gastralia were the fewest and thickest among all pterosaurs, forming ventral support to counteract the large moment arm the developed from the fulcrum at the dorsal/sacral interface. The sternal comnplex had a larger cristospine and sharper corners. The scapula was smaller than the coracoid. The deltopectoral crest of the humerus was strongly pinched. The pteroid was enlarged. Manual 4.1 was relatively longer. Manual 4.4 was shorter. The pelvis was larger and the pubis contacted the ventrally expanded ischium leaving a large circular obturator foramen between them. The hind limb and foot were larger, as in Muzquizopteryx.

Nyctosaurus sp. the Lincoln Nebraska state museum specimen 
Distinct from Nyctosaurus gracilis, the dorsals of the Nebraska specimen (Brown 1978, 1986) UNSM 93000, were relatively shorter. The scapula and coracoid were more robust. The deltopectoral crest of the humerus most closely resembled that of Muzquizopteryx. Fingers 1-3 were tiny vestiges. Manual 4.1 extended to mid ulna when folded. Manual 4.4 was probably fused to m4.3 or it was missing and m4.3 became curved. The pubis and ischium did not touch, as in more primitive nyctosaurs. It would have been impossible for the forelimb to develop thrust during terrestrial locomotion. It was likely elevated or used like a ski-pole.

Nyctosaurus sp. – two private crested specimens
Nyctosaurus sp. private specimens KJ1 and KJ2 (Bennett 2003) were derived from a sister to the Nebraska specimens of Nyctosaurus sp. and represent the last of their lineage with no known descendants. Distinct from the Nebraska specimen, the skull of KJ1 (below) had an enormous bifurcated frontal crest and a longer mandible than rostrum. The upper temporal fenestra was not visible in lateral view. The mandible was extremely sharp and ideal for skim or stab fishing. A notarium (fused dorsal vertebrae) was present. The coracoid was smaller and fused to the scapula. The humerus and deltopectoral crest were robust. The extensor tendon process was fused to the first wing phalanx. The pteroid was longer than in other nyctosaurs. Manual 4.1 was not much longer than the metacarpus. In KJ1 it was no longer than the metacarpus. The pelvis was deeper than shorter. The tibia was shorter. Overall KJ2 was slightly larger than KJ1. Contra Bennett (2003) not all Nyctosaurus had a crest. A crest does not mean these were male specimens.

Other “Big” Nyctosaurus specimens
As shown above (Figure 1), most Nyctosaurus were roughly the same size, but there is evidence of larger specimens. The largest was YPM 2501 (above). Bennett 1992 considered a pelvis, KUVP 993, in the size range of Pteranodon to be a female pelvis, but morphologically it belongs to a very large Nyctosaurus. Bennett (2000) also reported on a very large Nyctosaurus skeleton in an abstract. “…although incomplete, is the largest known specimen of Nyctosaurus with an estimated wingspan of 4.5 m.” Such a Nyctosaurus is shown in gray in figure 1, scaled up from the UNSM specimen.

In Summary
Unlike Pteranodon, the ancestry of Nyctosaurus included a very small taxon, No. 13, mislabeled Pterodactylus by Wellnhofer (1970). After that point all subsequent taxa, no matter how large (including YPM 2501) did not fuse the extensor tendon process or the scapula to the coracoid, until we come to the derived crested and privately held nyctosaurs, KJ1 and KJ2. They alone had a notarium, fused the scapula to the coracoid and fused the extensor tendon process to the first wing phalanx. Thus nyctosaurs, like all other pterosaurs, followed lepidosaur growth patterns as shown by phylogenetic analysis. Some nyctosaurus (and pterosaurs like ornithocheirids) grew to adults without fusion. Others fused certain bones.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992.
 
Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 2000. New information on the skeletons of Nyctosaurus. Journal of Vertebrate Paleontology 20 (Supplement to Number 3):29A.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153.
Bennett SC 2003. New crested specimens of the Late Cretaceous pterosaur Nyctosaurus.Paläontologische Zeitschrift 77: 61-75.
Bonner OW 1964. An osteological study of Nyctosaurus and Trinacromerum with a description of a new species of Nyctosaurus. Unpublished Masters Thesis, Fort Hays State University, 63 pages.
Brown GW 1978. Preliminary report on an articulated specimen of Pteranodon Nyctosaurus)gracilis. Proceedings of the Nebraska Academy of Science 88: 39.
Brown GW 1986. Reassessment of Nyctosaurus: new wings for an old pterosaur. Proceedings of the Nebraska Academy of Science 96: 47.
Frey E, Buchy M-C, Stinnesbeck W, González AG, and di Stefano A. 2006. Muzquizopteryx coahuilensis n.g., n. sp., a nyctosaurid pterosaur with soft tissue preservation from the Coniacian (Late Cretaceous) of northeast Mexico (Coahuila). Oryctos 6:19-39.
Miller HW 1972. 
The taxonomy of the Pteranodon species from Kansas. Transactions of the Kansas Academy of Science 74: 1–19.
Williston SW 1902a. On the skeleton of Nyctodactylus, with restoration. American Journal of Anatomy 1: 297–305.
Williston SW 1902b. On the skull of Nyctodactylus, an Upper Cretaceous pterodactyl. Journal of Geology 10: 520–531.

wiki/Nyctosaurus