Pterosaur Fingers – Part 1, Basal Taxa and Dimorphodontids

Most pterosaur workers pay little attention to the hands of pterosaurs. That’s unfortunate. Here many traits, including the relative lengths of the metacarpals and manual phalanges, were found to be as distinctive and phylogenetically informative as the relative lengths of the metatarsals and pedal phalanges reported in the catalog of pterosaur pedes (Peters 2011). In today’s blog we’ll examine the hands of a basal clade of pterosaurs (Fig. 1), highlighting only a few outstanding traits and ignoring the wing finger. We’ll continue the examination of other pterosaur fingers in later blogs. Today it is not important which way the fingers flexed, but if you’re interested, look here.

Figure 1. Pterosaur fingers. Click to enlarge. Red arc arrow indicates twisted phalanges to show ungual shape. Otherwise blue shapes indicate ungual shape.

Basal Pterosaurs and Dimorphodontids
The configuration of the basal pterosaur manus reflects its fenestrasaur ancestors, like Cosesaurus, Sharovipteryx and Longisquama. The latter two and perhaps all three were derived late survivors of the original splits that produced pterosaurs. The elongation (asymmetry) of the lateral metacarpals and lateral digits goes back to a basal tritosaur lizard, Huehuecuetzpalli. The trend in several pterosaur lineages was toward a greater symmetry in the metacarpals and (less often) the digits.

MPUM 6009 – The manus of the most primitive pterosaur(Fig. 1) was relatively smaller than that of its phylogenetic predecessor, Longisquama and distinct in terms of metacarpal and phalanx proportions. In MPUM 6009 metacarpal 1 was ~60% the length of metacarpal 3, which was just shorter than metacarpal 4. Metacarpal 3 was more than half the diameter of metacarpal 4. Manual 1.1 was twice the length of m2.1. Digits 1 and 2 were subequal and shorter than digit 3.

Austriadactylus – In both of the pterosaurs attributed to Austriadactylus metacarpal 1 was relatively longer. Metacarpal 3 was more gracile and as long as metacarpal 4. Manual 1.1 was relatively smaller. Digit 2 was longer than digit 1.

GLGMV-0002 – This basal dimorphodontid had a more robust metacarpal 4. Manual 3.2 was shorter.  Digit 3 was relatively shorter and shorter than metacarpals 3 and 4.

Dimorphodon micronyx – The metacarpals were all relatively shorter and digit 3 was longer creating more asymmetry in relative finger length.

Preondactylus -The phalanges of digit 3 were more similar in length.

Peteinosaurus – Metacarpal 4 was more gracile as were the fingers and unguals. Digit 3 was 50% longer than digit 2.

MCSNB 8950 – Longer metacarpals appear. Manual 2.1 was longer. Manual 3.2 was shorter.

IVPP embryo – The IVPP embryo comes form the Early Cretaceous and thus represents a late-surviving representative of a Late Triassic/Early Jurassic radiation. Metacarpal 4 was longer and more robust, and wider than mc1-3 combined. Metacarpals 1-3 were more gracile and essentially subequal in length. Digits 1-3 were more gracile and relatively shorter and shorter than the metacarpus. The penultimate phalanges were subequal.

Dimorphodon? weintraubi – Metacarpal 4 was not much more robust than mc1-3. While mc1 remained slightly shorter than mc3, all three metacarpals were aligned. The digits were longer than the metacarpus. The digits were less asymmetric. Manual 3.2 was no longer than wide.

Anurognathids

Dendrorhynchoides – Metacarpals 1-3 remained robust and subequal. Digits 2 and 3 were subequal. Manual 2.1 and m 3.1 were subequal and short.

The Flathead anurognathid, SMNS 81928) – Here metacarpals 1-3 were aligned, but mc1 was the longest in the set. Manual 2.1 was as long as m3.1+m3.2 and aligned with m1.1. Manual 3.3 was longer than m2.2.  Digits 2 and 3 were nearly subequal. Manual 2.1 was subequal to m3.1+m3.2.

Anurognathus ammoni – Metacarpal 4 was more robust and shorter such that the pulley joint was half the length of metacarpal 4. Metacarpal 4 was slightly shorter than mc1-3, which were subequal to each other. Manual 2.1 was half as long as m3.1. Manual 2.2 was subequal to m3.3. The unguals were nearly as long as the penultimate phalanges.

CAGS IG 02-81 – Manual 2.1 was subequal to m3.1 in this pterosaur attributed to Jeholopeterus. Metacarpal 4 was not so robust, similar to mc 1-3. Manual 3.2 was shorter than wide.

Jeholopterus – The metacarpus was relatively longer than in the CAGS specimen. Metacarpal 3 was the shortest. Metacarpal 1 was subequal to mc4. Digit 2 was slightly longer than digit 3. Distinct from other anurognathids and other pterosaurs, the unguals were narrow, strongly curved and elongated like surgical needles. This trait, among others, led to the hypothesis of vampirism in this taxon.

Batrachognathus – Metacarpal 4 was short and very robust with a broader base than in Anurognathus. Metacarpals 1-3 were shorter than mc4. Digits 1-3 were subequal. Manual 3.2 was a disc. Manual 1.1 was longer than m3.2 and m4.3. The unguals were shorter than in Jeholopterus.

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
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605

The Strange and Tiny Feet of Ornithocheirid Pterosaurs

Some pterosaurs lost their teeth. Some reduced their tail. In ornithocheirid pterosaurs the feet became incredibly small (Peters 2011, Fig. 1).

Bird Analogs
Among living birds, the apodiformes (swifts and hummingbirds) have the smallest feet. These birds rarely walk.

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

The Reduction of the Pes in Ornithocheirids
Ornithocheirids are characterized by their toothy beaks and giant wings. The most primitive forms, like Yixianopterus and the JZMP embryo, had relatively typical proportions overall. That changes with Boreopterus in which the feet were greatly reduced. Derived taxa, like Anhanguera (Fig. 2), further reduced the metatarsus, producing feet with atypical proportions. Note the relative size of pedal digit V (Figs. 2-4), which did not phylogenetically shrink in proportion to the rest of the pes. Instead digit 5 regains more primitive proportions not seen since Scaphognathus.

Anhanguera
The pterosaur foot with the most atypical proportions belongs to Anhanguera (Fig. 2), the most derived of the ornithocheirids. The metatarsus was reduced to shorter than the proximal phalanges. Metatarsal 4 was shorter than the unguals! This arrangement gave the foot the maximum toe/metatarsal ratio, which was important because the webbed toes were used to automatically extend the horizontal hind limbs while airborne.

By the way, the atypical length of metatarsal 1 relative to the others is a key trait uniting ornithocheirids with cycnorhamphids and scaphognathids going back to Jianchangnathus.

Figure 2. Anhanguera pes. This, the most derived ornithocheirid, had the most derived foot with reduced metatarsals. The pes was largely disarticulated and had to be pieced together according to PILs (parallel interphalangeal lines) and the patterns of closest known sister taxa.

Prior to 2010 (see below), ornithocheirid feet were not described. Wellnhofer (1985) and Kellner and Tomida (2000) overlooked the tiny feet of Anhanguera, restoring it with a standardized and standard-sized foot. Wang et al. (2005) described Nurhachius but overlooked the pes except to identify it on the in situ fossil. In the late 1990s Anhanguera was the first ornithocheirid in which I noticed the feet were so small (not published until Peters 2011). Subsequent discoveries confirmed this trait.

Figure 3. Pes of Zhenyuanopterus. Left: Cast. Right: Tracing with digit 5 reconstructed. Pedal 5.2 appears to have been split in situ and graphically repaired at lower right. Note the large relative size of digit 5 brought about my reduction of the rest of the foot. Traditional hypotheses do not admit the existence of a large pedal digit 5 in "pterodactyloid"-grade pterosaurs.

Zhenyuanopterus
Lu (2010) described the best preserved ornithocheirid, Zhenyuanopterus, for the first time noting its tiny feet (Figs. 2 and 3) which were perfectly preserved and fully articulated. This is one of the few ornithocheirids with a shorter metatarsal 1 than mt2.

Figure 4. Zhenyuanopterus in lateral view, reconstructed pes enlarged at right.

Plantigrade Tiny Feet Rarely Used
The fragile and tiny size of the feet of ornithocheirids suggests they were rarely used. These prehistoric albatross analogs might have spent days to weeks airborne, perhaps nesting in areas free from predators.

Behavioral Correlates
It seems unlikely that pterosaur feet could have evolved to become even smaller. Terrestrial locomotion was probably slow and methodical, reducing the stress of each fragile footfall. Despite reduced feet, the toes remained beneath the shoulder glenoid, the center of balance in all flying reptiles. So it was possible for the wings to be extended for flying, sunning or display while standing erect and very finely balanced on such tiny toes.

Hatchlings with Large Feet?
The JZMP embryo had relatively large (for an ornithocheirid) feet. At present this appears to be a phylogenetic character due to its nesting prior to Boreopterus. Nevertheless it seems reasonable that hatchling ornithocheirids might have had larger feet that did not grow in step with the rest of the body. Counter this notion, the hatchling Pterodaustro had relatively smaller feet than the adult.

The Prepubis 
Perhaps it is no coincidence that the prepubis is rarely found in ornithocheirids. Where it is found (Arthurdactylus, SMNK PAL 1136), the prepubis is relatively small. The prepubis effectively lengthens the pubis providing anchors for femoral adductors. These would be less useful in a pterosaur that rarely walked, hence the reduction )and perhaps loss) of the prepubis in certain ornithocheirids.

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
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, Tokyo, Monographs, 17: 1-135.
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.
Peters D. 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
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.
Wellnhofer P 1985. Neue Pterosaurier aus der Santana-Formation (Apt) der Chapada do Araripe, Brasilien. Paläontographica A 187: 105–182.

wiki/Nurhachius
wiki/Zhenyuanopterus

Tikiguania Not a Triassic Squamate? No Problem! Plenty of Others!

A Rare Double Post – This Just In:
Abstract (from Hutchinson et al. 2012) – Tikiguania estesi is widely accepted to be the earliest member of Squamata, the reptile group that includes lizards and snakes. It is based on a lower jaw from the Late Triassic of India, described as a primitive lizard related to agamids and chamaeleons. However, Tikiguania is almost indistinguishable from living agamids; a combined phylogenetic analysis of morphological and molecular data places it with draconines, a prominent component of the modern Asian herpetofauna. It is unlikely that living agamids have retained the Tikiguania morphotype unchanged for over 216 Myr; it is much more conceivable that Tikiguania is a Quaternary or Late Tertiary agamid that was preserved in sediments derived from the Triassic beds that have a broad superficial exposure. This removes the only fossil evidence for lizards in the Triassic. Studies that have employed Tikiguana for evolutionary, biogeographical and molecular dating inferences need to be reassessed.

This Does Not Remove the Only Fossil Evidence for Lizards in the Triassic
…because we have a third clade of lizards, the Tritosauria, that were widespread during the Triassic. Tritosaurs include Tanystropheus, Macrocnemus, drepanosaurids, fenestrasaurs (including pterosaurs) and their kin. At the base of that clade was Lacertulus from the Late Permian.

Other basal tritosaurs include Huehuecuetzpalli, Meyasaurus and the Daohugo enigma, all from the Early Cretaceous. These demonstrate the other side of the coin for Tikiguania: late-survivor status virtually unchanged from a phylogenetic origin in the Permian or Triassic.

Oh, did I mention the tuatara, Sphenodon? The coelocanth, Latimeria? Hey guys, morphologies unchanged over tens to hundreds of millions of years can happen.

It’s Heretical, Based on a Larger Inclusion Set
Tikiguania may be Quaternary in origin. It doesn’t matter. That doesn’t remove squamates from the Triassic. The Tritosauria, while overlooked, still counts. A larger inclusion set shows the way.

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
Hutchinson MH, Skinner A and Lee MSY 2012. Tikiguania and the antiquity of squamate reptiles (lizards and snakes). Biology Online published before print. doi: 10.1098/rsbl.2011.1216

A 4th Finger Imprint in the Haenamichnus Pterosaur Track?

Tracks attributed to pterosaurs are now known worldwide. The largest such tracks have been rightly attributed to giant azhdarchid pterosaurs like Quetzalcoatlus. The  Haenamichnus trackway (Hwang et al. 2002, Fig. 1) leaves no doubt as to the identity of the trackmaker, but the individual impressions differ greatly from one another and are indistinct at best. It must have been a wet, muddy day when these were produced. Sometimes the manus and pes impressions are separate, but often they glob together.

Figure 1. Yellow arrow points to a possible 4th digit imprint in the trackway of Haenamichnus. Note how messy these muddy tracks are. Not much detail in each one. Only the walking pattern (on right) is precise. Note that Step 7 is the only one without a pes imprint, unless that medial shape IS the pes imprint.

Step 7
Among the many Haenamichnus ichnites (Fig. 1), step 7 is interesting because it appears to impress an oddball fourth impression medially between #1 and #3. What could it be?  In other pterosaurs or, for that matter, in other ichnites within this trackway digit 4, the wing finger, did not leave impressions. The wing finger was carried vertically, folded against the arm during terrestrial locomotion and the knuckle was elevated above the substrate. If digit 4 DID make that impression, why was the impression bent and so short? After all, digit 4 was a long straight bone that terminated in a large knuckle.

The first guess: The odd shape is the (otherwise missing) pes impression, blended into the manus impression. And with that, perhaps I need go no further… but I will.

The second guess:  The odd shape is the first impression of manual digit 3 before it was lifted and repositioned, rotated on the axis of the impression of digit 1. If so, the pes did not make an impression. In this case the pes might have hit a dry spot or was later obliterated.

The third guess:  Whatever geological thing that discoloration or dip was, it was there before the pterosaur touched it and remained afterwards.

Don’t be fooled by those who say: four impressions = four digits. Critical thinking, and the lack of similar traces in other pterosaurs argue against such snap judgements.

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
Hwang KG, Huh M, Lockley MG, Unwin DM and Wright JL 2002. New pterosaur tracks (Pteraichnidae) from the Late Cretaceous Uhangri Formation, southwestern Korea. Geology Magazine 139(4): 421-435.

Tail-Assisted Pitch Control in Lizards (and Pterosaurs)

A recent paper entitled “Tail-assisted pitch control in lizards, robots and dinosaurs” (Libby et al. 2012) reported, “… lizards control the swing of their tails in a measured manner to redirect angular momentum from their bodies to their tails, stabilizing body attitude in the sagittal plane.” They also reported, “Our dynamics model revealed that a body swinging its tail experienced less rotation than a body with a rigid tail, a passively compliant tail or no tail.”

As in Dromaeosaurs
Libby et al. (2012) introduced their abstract with this statement, “In 1969, a palaeontologist proposed (Ostrom 1969) that theropod dinosaurs used their tails as dynamic stabilizers during rapid or irregular movements, contributing to their depiction as active and agile predators.” This hypothesis has been widely accepted. Archaeopteryx is an example of such a morphology.

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

Applicable to Fenestrasaurs and Pterosaurs?
The stiff attenuated tail of Cosesaurus, Sharovipteryx, Longisquama and basal pterosaurs bears strong similarities to the tail of Archaeopteryx and dromaeosaurs, especially so in derived long-tailed pterosaurs, like Rhamphorhynchus in which the various zygopophyses and chevrons elongated and intertwined with one another in much the same fashion leaving only the proximal caudals free to move. In birds the short tail and long tail feathers may flex dorsally and ventrally to enhance balance. The same seems to hold true for fenestrasaurs and pterosaurs (as lizards themselves). Both birds and fenestrsaurs largely reduced the caudofemoralis muscles and their bony caudal anchors diminishing the ability to swing the tail left and right.

The Arboreal Leaping Theory for the Origin of Pterosaurs
Bennett (1997) proposed a leaping behavior for the origin of pterosaurs. Bennett (1997) used hypothetical models. My studies with the increasingly long-legged and bipedal pterosaur ancestors Cosesaurus, Sharovipteryx, Longisquama and MPUM 6009 confirm a leaping origin, with the addition of bipedal digitigrade locomotion (reversed in several derived pterosaurs). Libby et al. (2012) tested lizard leaping in the laboratory replicating behaviors that these fenestrasaurs likely practiced in the Triassic wild.

Figure 2. Click to enlarge. The most primitive known pterosaur, the Milan specimen, MPUM 6009.

Elevating the Tail Permanently in Basal Pterosaurs
In lizards and derived pterosaurs the tail was held in line with the sacrum and dorsal vertebrae, but in Longisquama and basal pterosaurs (Fig. 2) the sacrum and posterior ilium was elevated distally, at right angles to the anterior ilium. This permanently elevated the base of the tail, similar enough to long-tailed lemurs and house cats. Despite the low mass of an attenuated fenestrasaur/pterosaur tail, elevation provided tail clearance from the substrate while standing with the shoulders elevated above the hips. It also moved the center of gravity anteriorly with dynamic possibilities (flight, with a center of balance at the shoulder joint). Thirdly a vane on the tail tip in derived long-tailed pterosaurs likely provided a secondary sexual signal, as blogged earlier.

Lowering the Tail Permanently in Derived Pterosaurs
Later pterosaurs reversed this early configuration, straightening out the posterior ilium and sacrum, perhaps as the proximal caudal vertebrae evolved more flexibility. An elevated tail would not have been as aerodynamic as an in-line tail so this was probably also a factor.

Figure 3. The Jayne lab documents bipedal locomotion in Callisaurus.

How Living Lizards Run Bipedally
The Bruce Jayne Lab in Cincinnati, Ohio, has produced a video of a zebra-tailed lizard (Callisaurus, Fig. 3) in fast quadrupedal and bipedal locomotion filmed on a treadmill. Note the horizontal configuration of the spine and tail, similar to the configuration reconstructed in Sharovipteryx. Compare this to the video of the basilisk (Jesus lizard) running more erect with an elevated tail, similar to the reconstruction of Longisquama (Fig. 1). Another living lizard, the Australian frilled lizard (Chlamydosaurus kingii, Fig. 4) also had an erect carriage when bipedal.

Fig. 4 Chlamydosaurus, the Austrlian frill-neck lizard with an erect spine and elevated tail. Image courtesy of R. Shine, published in Peters 2000.

A Dynamic Tail and Probable Behaviour Patterns in Fenestrasaurs
Sharovipteryx did not have much of an elevated posterior ilium and tail (Fig. 1), but Longisquama did. The difference appears to be related to stance and problems with tail/substrate clearing due to stance. Sharovipteryx had such long hind limbs that tail clearance was not an issue. The morphology of Longisquama, with its short neck, large grasping hands and strong leaping legs has been compared to modern long-tailed lemurs, which actively leap from tree to tree and cling to vertical tree trunks. Basal pterosaurs were also likely tree clingers judging by their ability to grasp medial columns with forelimbs otherwise unable to pronate and supinate.

The Reduction of the Long Tail in Derived Pterosaurs
According to cladistic analysis the reduction of the long, stiff tail in basal pterosaurs occurred by convergence three times: 1) after the proto-anurognathid MCSNB 8950; 2) after Dorygnathus (SMNS 50164); after Dorygnathus (Up R 156) and 3) after Scaphognathus (the Maxberg specimen) (Fig. 5). The last of these is the only one in which the tail demonstrates extreme reduction in length and depth. Most workers agree that subtle refinements and improvements in aerodynamic abilities elsewhere in the pterosaur anatomy reduced the need for dynamic stablization from a long, stiff tail.

Figure 5. These four small to tiny pterosaurs demonstrate tail reduction following taxa having a longer and more robust tail.

The Pattern of Tail Reduction in Pterosaurs
At some point the utility of an elongated tail diminished in pterosaurs, as it did in birds. Contra traditional stuides, tail reduction in pterosaurs appeared three times during overall size reduction in pterosaurs. Examples include the tiny Dorygnathus sisters TM 10341, St/Ei I and the tiny Scaphognathus sister, TM 13104 (Fig. 5). These reductions may be considered paedomorphic sequences in which the genes for tail lengthening and stiffening simply did not turn on as these three pterosaur clades retained embryonic traits (a flexible tail curled into a shell) earlier and earlier in their ontogenetic development.

The Pterodaustro Tail
The tail of derived pterosaurs has been rarely documented, but in Pterodaustro (Codorniu 2005) a comparatively elongated tail was present. Kellner and Tomida (2000) documented the tail of Anhanguera. Young (1964) documented the tail of Dsungaripterus. Zhenyuanopterus preserved a completely articulated tail. These were all substantial tails, yet still relative vestiges. Traditional views promote the disappearance of tails in pterodactyloid-grade pterosaurs. Not so, according to these derived examples.

The Pteranodon Tail
Bennett (1987 ) described an unusual tail attributed to Pteranodon that had duplex centra capable only of elevation and depression. This tail terminated in extended parallel rods, probably representing fused duplex centra. This tail was likely too small to affect aerodynamic abilities. If present on a female, such a tiny fragile tail might have been in danger of damage during mating. Perhaps it was capable of curling over the back to permit mating without damage, co-opting the tail-assisted pitch control of its nonvolant lizard ancestors.

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 1987.  New evidence on the tail of the pterosaur Pteranodon (Archosauria: Pterosauria). Pp. 18-23 in Currie, P. J. and E. H. Koster, eds. Fourth Symposium on Mesozoic Terrestrial Ecosystems, Short Papers. Occasional Papers of the Tyrrell Museum of Paleontology, #3
Bennett SC 1997. The arboreal leaping theory of the origin of pterosaur flight. Historical Biology 123: 265–290.
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 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.
Codorniú LS 2005. Morfología caudal de Pterodaustro guinazui (Pterosauria: Ctenochasmatidae) del Cretácico de Argentina. Ameghiniana: 42 (2): versión On-line ISSN 1851-8044.
Libby T, Moore TY, Chang-Siu E, Li D, Cohen DJ, Jusufi A, Full RJ 2012. Tail-assisted pitch control in lizards, robots and dinosaurs. Nature. 2012 Jan 4;481(7380):181-4. doi: 10.1038/nature10710.
Ostrom JH 1969. Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Bull. Peabody Mus. Nat. Hist. (Paris) 30, 68–80, 144. Young CC 1964. On a new pterosaurian from Sinkiang, China. Vertebrata PalAsiatica 8: 221-256.

Biseridens: at the Base of the Anomodontia? No.

A recent Journal of Vertebrate Paleontology Memoire provided much needed and appreciated insight into the speciation of Dicynodon (Kammerer, Angielczyk and Fröbisch 2011), the dicynodont that gave its name to the clade. In their excellent phylogenetic analysis of the dicynodontia, these authors unfortunately placed Biseridens (Liu et al. 2009) at the base.

Testing That Nesting
In a study of basal therapsids, including many not considered by Kammerer, Angielczyk and Fröbisch (2011), Biseridens nested between Syodon and Titanophoneus, not at the base of the Dicynodontia. At the base of the Dicynodontia we find Nikkasaurus, Niaftasuchus, Microurania and Tiarajudens preceding Dicynodon (Fig. 1). That means the tusks of dicynodonts were secondarily developed after loss in earlier and more basal taxa.

Figure 1. The family tree of the Therapsida including the Dicynodontia. Click to enlarge. Note the position of Biseridens prior to Titanophoneus and Jonkeria, two taxa not tested in the Dicynodon study. Other pertinent taxa excluded from the Kammerer et al. (2012) study include: Nikkasaurus, Niaftasuchus, Microurania and Tiarajudens.

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
Kammerer CF, Angielczyk KD and Fröbisch NJ 2011. A comprehensive taxonomic revision of Dicynodon (Therapsida, Anomodontia) and
its implications for dicynodont phylogeny, biogeography, and biostratigraphy. Journal of Vertebrate Paleontology 31, Supplement 1: 1-158
DOI:10.1080/02724634.2011.627074
Liu J, Rubidge B and Li J 2009. A new specimen of Biseridens qilianicus indicates its phylogenetic position as the most basal anomodont. Proceedings of the Royal Society B 277 (1679): 285–292.

wiki/Biseridens

Panphagia (2009) = Pampadromaeus (2011)

Figure 1. Panphagia protos with a closeup of the skull. Note how slender the pubis is in lateral view.

Panphagia protos
Martinez and Alcobar 2009 described a small, basal dinosaur that nested at the base of the Sauropodomorpha. I ran the traits of Panphagia protos through the large reptile matrix and every one matched up to Pampadromaeus (Cabreira et al. 2011). Likely not conspecific, the two appear to be congeneric. Panphagia protos (Martinez and Alcobar 2009) has seniority. The ilium is more robust in Pampadromaeus. The scapula is more robust in Panphagia. Both nested between theropods and phytodinosaurs, basal to Daemonosaurus.

Figure 2. Pampadromaeus in left lateral view from Cabreira et al. 2011.

The Pubis
The pubis in lateral view is very slender (but not in anterior view). This is the first clue I’ve seen as to the origin of the retroverted slender pubis in ornithischia, a clade that originated in sister taxa to basal sauropodomorpha like Panphagia.

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
Cabreira SF, Schultz CL, Bittencourt JS, Soares MB, Fortier DC, Silva LR and Langer MC 2011. New stem-sauropodomorph (Dinosauria, Saurischia) from the Triassic of Brazil. Naturwissenschaften (advance online publication) DOI: 10.1007/s00114-011-0858-0

Martínez RN and Alcober OA 2009. A basal sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha (pdf). PLoS ONE 4 (2): 1–12. doi:10.1371/journal.pone.0004397. PMC 2635939. PMID 19209223. online article

wiki/Panphagia

Why Pterosaurs Are Extinct Today

The K/T Extinction Event
Everyone knows that pterosaurs, dinosaurs and a host of other prehistoric reptiles died out at the K/T (Cretaceous/Tertiary) boundary ~65 mya. But SOME birds, lizards, turtles, crocs and mammals survived. So, why did ALL pterosaurs die out?

Phylogenetic Analysis 
As in dinosaurs, the pterosaurs we know from the latest Cretaceous were not the same pterosaurs living in the Triassic, Jurassic or Early Cretaceous. All of these earlier pterosaurs became extinct, but a few genetic lines survived by evolving into the Late Cretaceous forms we know and love. Phylogenetic analysis indicates that certain lucky Middle Jurassic Dorygnathus specimens ultimately evolved (via several transitional taxa) into Quetzalcoatlus, Pteranodon, Nyctosaurus, Tupuxuara and any other Late Cretaceous pterosaurs I’m forgetting (the current list is not much longer than this).

The Example of Dorygnathus
Analysis illustrates how the descendants of Dorygnathus changed in size and shape as they evolved into the above Late Cretaceous taxa. Therein, l think, lies the answer to why pterosaurs were not able to continue evolving into the modern day.

Figure 1. The Azhdarchidae. Click to enlarge.

Size Matters
If we were to follow the lineage of Dorygnathus through Quetzalcoatlus (Fig. 1) we would meet the following taxa in order: Dorygnathus (SMNS 50164), Pterodactylus? spectabilis (TM 10134), Beipiaopterus, No. 44, No. 42, Jidapterus, Chaoyangopterus, Zhejiangopterus and finally the two species of Quetzalcoatlus. Setting aside the huge size differences between the two Qs and their phylogenetic predecessor, Zhejiangopterus, note that tiny TM 10134 and two other tiny pteros, No. 42 and No. 44, are in this line-up.

Tiny Survivors
In the Late Jurassic the genetic lineage of Dorygnathus, of the Middle Jurassic, was represented by a tiny version of itself, TM 10134. There were no other full-size Dorygnathus present in the Late Jurassic. Something killed every other one over a certain size. Only tiny dory descendants somehow survived. Was it because of their size?

Major Morphological Changes in Tiny Taxa
As mentioned above (Fig. 1) other Late Jurassic tiny dorygnathids also include No. 42 and No. 44, both of which evolved a slender elongated neck, a low trostrum, smaller teeth and longer more gracile limbs. These traits were retained in all later and larger azhdarchids and huanhepterids (Fig. 1). (Pterorhynchids, scaphognathids and ctenochasmatids were also Dorygnathus descendants you can read about here, here and here).

Good Times
When the threat of extinction did not loom over pterosaurs, they tended to become bigger. Evidently this was especially true during the latest Cretaceous because pterosaurs reached their greatest sizes right at 65 million years ago.

Not Being Small Is What Killed Late Cretaceous Pterosaurs
Just as being small saved many pterosaur lines earlier, being small saved many other vertebrates following the K/T mass extinction event. Big vertebrates did not survive. Unfortunately the giant pterosaurs of the latest Cretaceous could not breed small enough to save themselves, as their ancestors had done. We don’t find any pterosaurs smaller than Nyctosaurus in the Late Cretaceous.

Serial Size Reduction and How It Happens
ln pterosaurs phylogenetic size reduction from Dorygnathus to TM 10134 was made possible by reaching sexual maturity at half their final size (Chinsamy et al. 2008). Smaller pelves would have passed smaller eggs, smaller hatchlings and an even smaller second generation in serial fashion. Smaller vertebrates typically have a relatively faster maturation process, creating more tiny hatchlings earlier and at a faster clip. This increase in reproductive rates raised the odds that whatever was killing the larger, slower-to-breed individuals could be overcome by an acceleration in breeding, producing an acceleration in genetic variation and mutation. Such a serial size reduction pattern occurred at the base of nearly every major clade within the Pterosauria. When the same process is observed about a dozen times that verifies its veracity.

Figure 2. Phony pterosaur.

If only some tiny pteros existed at the Late Cretaceous, we might have some “thunderbirds” flying around today (Fig. 2).

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
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.

Another Look at Amotosaurus

Figure 1. Amotosaurus reconstructed from data in Fraser and Rieppel (2006).

Amotosaurus rotfeldensis SMNS 50830 (Wild 1980) was originally considered a juvenile Tanystropheus antiquus, but Fraser and Rieppel (2006) determined that only eight cervicals were present, a shagreen of denticles covered the vomers, palatines and pterygoids, the second sacral rib was bifurcate, the tarsus was well-ossified and three distal tarsals were present. Due to the ossified tarsus they considered the small specimen an adult.

Ooops…
Unfortunately Fraser and Rieppel (2006) reported that Langobardisaurus had 12 rather than 8 cervicals and so missed an important shared trait. Here Amotosaurus nests with Langobardisaurus and they shared a longer mt 4 relative to mt 3 among several other characters. The scapula is much enlarged in Amotosaurus, as in Tanystropheus. The ventral pubis and ischium are in contact with one another, as in Cosesaurus, which also shares a longer metatarsal 4. The mandible is ventrally concave as in Langobardisaurus. The posterior teeth are difficult to see, but there seems to be little indication of anything but simple compressed cone shapes present, as in Tanystropheus. Pedal 5.1 was relatively shorter.

Protorosaur? No.
Protorosaurus nested near the base of the Archosauriformes. Langobardisaurus and Amotosaurusnested within the Lepidosauriformes, within the Tritosauria.

Why Ignore Langobardisaurus?
In their conclusion,  Fraser and Rieppel (2006) practically ignored Langobardisaurus. They reported, “At present it can be said that Amotosaurus probably occupies a position intermediate between Tanystropheus and Macrocnemus.” According to the present tree, that’s a position currently occupied by Langobardisaurus, here considered the closest sister of Amotosaurus and similar in size.

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
Fraser NC and Rieppel O 2006. A new protorosaur (Diapsida) from the upper Bundsandstein of the Black Forest, Germany. Journal of Vertebrate Paleontology 26(4):866-871.
Wild R 1980. Tanystropheus (Reptilia: Squamata) and its importance for stratigraphy. Mémoires de la Société Géologique de France, N.S. 139:201–206.

Synaptichnium and Proterosuchus

Synaptichnium (Nopcsa 1923, Fig. 1) is a fairly large quadrupedal, semi-plantigrade ichnotaxon of the Early to Middle Triassic in which pedal digit 4 remains longer than digit 3, which is atypical for derived archosauriforms. Here (Fig. 1) the pes of Proterosuchus, a basal archosauriform with pedal digit 4 longer than 3, was slightly modified to fit the ichnite. This is appropriate because other less completely known proterosuchids, like Archosaurus and Sarmatosuchus are known. The manus of Proterosuchus is poorly known, but when matched to the impression of Synaptichnium, our guesses become more precise in that now we can model digit 4 shorter than digit 3 despite a lack of bone data. Similar data mining from ichnites occured in Erythrosuchus matched to Isochirotherium ichnites.

Figure 1. Synaptichnium compared to a slightly altered pes of Proterosuchus. Note a reduction of one phalanx in pedal digit 4 to match one less pad in the ichnite.

Comparisons to Prolacerta
Prolacerta is a predecessor taxon to Proterosuchus. The manus of Prolacerta is more clompletely known and it has a digit 4 longer than 3. To my knowledge, successor taxa to Proterosuchus do not  preserve a manus until one gets to Ticinosuchus, which also has a manual digit 4 shorter than 3.

Figure 2. Prolacerta. Note the relative lengths of the manual and pedal lateral digits. Click for more info.

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
Avanzini M and Mietto P 2008. The occurrence of the vertebrate ichnogenus Synaptichnium in the Anisian (Middle Triassic) of Southern Alps. Studi Trent. Sci. Nat., Acta Geol., 83 (2008): 259-265. online pdf
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Gower DJ and Sennikov AG 1997. Sarmatosuchus and the Early History of the Archosauria. Journal of Vertebrate Paleontology 17(1):60-73.
Nopcsa F 1923. Die Familien der Reptilien. Fortschritte der Geologie und Paläontologie der Rheinlande und Westfalens. 210 pp.
Sennikov AG 1994. Pervyj srednetriansovyj proteroscchid iz Vostochnoy Evropy. Doklady Akademii Nauk 336:359-661.
Tatarinov LP 1960. Otkrytie pseudozhukhii v verkhnei permi SSSR: Paleontologischeskii Zhurnal, 1960, n. 4, p. 74-80.

wiki/Proterosuchus