The other Dimorphodon skull (BMNH R 1035) unscrambled

We know of
several Dimorphodon (Buckland 1829, Owen 1859) Hittangian, Early Jurassic ~195 mya) specimens from Europe.

  1. BMNH (NHUK PV) R1034a Mary Anning’s discovery and the holotype, a misarticulated skeleton lacking a skull and tail (Fig. 1)
  2. BMNH (NHUK PV) R 1035 includes a skull, cervicals and wings (Figs. 1, 2)
  3. BMNH 41212 is a nearly complete specimen lacking a tail (Fig. 1).
  4. BMNH? a complete tail (Fig. 1)
  5. Other BMNH specimens. presumably disarticulated bones
  6. YPM 350, YPM 9182 and other Yale specimens, several disarticulated bones including a partial skull

Dimorphodon? weintraubi (IGM 3494, Clark et al. 1994, 1998; Early to Middle Jurassic, ~175 mya) nests several nodes away, with basal anurognathids. It lived 20 million years later in North America.

Figure 1. The three most complete Dimorphodon specimens, BMNH 41212, BMNH R1034, and BMNH R1035.

Figure 1. The three most complete Dimorphodon specimens, BMNH 41212, BMNH R1034, and BMNH R1035. BMNH (British Museum of Natural History) used to be NHUK (Natural History United Kingdom).

The BMNH R1035 specimen of Dimorphodon
has not been figured very often because the skull is somewhat scrambled  Here it is traced (Fig. 2) and reconstructed (Fig. 1). It is quite similar to that of the BMNH 41212 specimen, with only slight modifications.

Figure 2. Dimorphodon specimen BMN R1035 with elements traced. Here the complete wing was recovered along with cervicals and occipital elements.

Figure 2. Dimorphodon specimen BMNH (formerly NHUK) R1035 with elements traced and segregated to reduce the chaos. Here the complete wing was recovered along with cervicals and occipital elements. Click to enlarge.

The ‘scrambled’ 1035 material differs
from the 41212 material in several traits:

  1. The naris is slightly larger relative to the antorbital fenestra
  2. The sclera ring is smaller
  3. The mandible is deeper
  4. The metacarpus and wing are longer

When you look up Dimorphodon online
at Wikipedia the authors do not identify D. weintraubi as an anurognathid. And they follow Clark et al. in asserting that Dimorphodon had plantigrade pedes based on the metatarsalphalangeal butt joint. We looked at that problem earlier here and Peters (2000) also covered that topic, but essentially the metatarsophalangeal butt joint was immobile, but the cylindrical interphalangeal joints provided the required extension to create a digitigrade pes that matches digitigrade pterosaur and Rotodactylus ichnites in which the proximal phalanges are always elevated. It’s a common pattern: Sometimes it takes the paleo crowed a long time to accept certain facts.

Figure 3. from Wikipedia, my sculpture of Dimorphodon now found in several museums. The curly-cue tail, anteriorly-planted fingers and plantigrade feet are all unnatural.

Figure 3. from Wikipedia, my sculpture of Dimorphodon now found in several museums. The curly-cue tail, anteriorly-planted fingers and plantigrade feet are all unnatural and not part of the original model.

And then, of course manual digit 5 and wing ungual
are both present in the 1035 specimen (Figs. 4, 5).

Figure 4. Wingtip ungual in the BMNH 1035 specimen of Dimorphodon.

Figure 4. Wingtip ungual in the BMNH 1035 specimen of Dimorphodon.

Yes, they are difficult to see
unless you look for them and trace them. But think how long it took to find hind limbs in fossil whales, known for over 150 years prior to that discovery.

Figure 5. Manus of the BMNH 1053 specimen of Dimorphodon highlighting vestigial digit 5 in pink.

Figure 5. Manus of the BMNH 1053 specimen of Dimorphodon highlighting vestigial digit 5 in pink.

A while back
Nesbitt and Hone 2010 attempted to show that the 41212 specimen of Dimorphodon had a mandibular fenestra in a desperate and misguided attempt at providing archosaur traits to pterosaurs. That was bogus, as noted earlier. Those two didn’t want to take into account the slipped surangular on the specimen. In the 1035 specimen the surangular is in place and no mandibular fenestra is present.

References
Buckland W 1829. Proceedings of the Geological Society London, 1: 127
Clark J, Montellano M, Hopson J and Fastovsky D. 1994. In: Fraser, N. & H.-D Sues, Eds. 1994. In the Shadows of Dinosaurs. New York, Cambridge: 295-302.
Clark J, Hopson J, Hernandez R, Fastovsk D and Montellano M. 1998. Foot posture in a primitive pterosaur. Nature 391:886-889.
Nesbitt SJ and Hone DWE 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233
Owen R 1859. On a new genus (Dimorphodon) of pterodactyle, with remarks on the geological distribution of flying reptiles.” Rep. Br. Ass. Advmnt Sci., 28 (1858): 97–103.
Nesbitt SJ and Hone DWE 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233
Padian K 1983. Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum, Postilla, 189: 1-44.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods. – Ichnos 7(1): 11-41.
Sangster S 2001. Anatomy, functional morphology and systematics of Dimorphodon. Strata 11: 87-88

wiki/Dimorphodon

 

How Did Pteranodon Walk?

Earlier we looked at terrestrial locomotion in pterosaurs, discriminating a basal bipedal taxon from the quadrupedal track makers that can be matched to tracks attributed to ctenochasmatid, pterodactyloid (check out the animation!) and maybe even ornithocheirid pterosaurs (Peters 2000, 2010, 2011). We also looked at the many potential problems that surround the wing launch hypothesis and presented an alternative or two.

Pteranodon and especially Nyctosaurus (Fig. 1) were two special cases united by extremely long metacarpals coupled with relatively short hind limbs that prevented them from walking in the same manner as pterosaurs having shorter metacarpals.

 

Nyctosaurus reconstruction

Figure 1. Nyctosaurus reconstruction according to Bennett (1997) and Peters, both based on UNSM 93000. Click to enlarge.

Bennett’s Take on Nyctosaurus
Bennett (1997) provided a great illustration of Nyctosaurus “essentially bipedal” (Fig. 1) because the forelimbs could only touch the substrate on the “back” of the folded wing finger, so far in front of the jaw tips that they were unable to provide a thrust vector to the elbow and shoulder. The fingers were greatly reduced, perhaps because they were no longer in use. See Muzquizopteryx and  Nyctosaurus bonneri for extreme proportions within this clade. Even shorter metacarpals on pterosaurs don’t appear to contribute thrust, only support, especially when nosing around for food items buried in the substrate or swimming around their submerged ankles in the shallows.

Pteranodon
The Triebold specimen of Pteranodon NMC41-358 is the most complete one known (Fig. 2). Others had larger wings and shorter legs. In the Triebold specimen it appears difficult for the free fingers (especially fingers 1 and 2) to contact the substrate as in other pterosaurs due to the great length of the metacarpus relative to the hind legs.

Pteranodon walking animated

Figure 2. Pteranodon walking. Click to animate. Note the femur is drawn and moves in the parasagittal plane for ease of animation. When properly sprawled the butt would drop a wee bit. The feet may have been plantigrade. They are not well preserved in this specimen. Other Pteranodon have digitigrade pedes. Those closer to UALVP 24238 had plantigrade pedes.

Too Erect?
If the above animation was configured too erect, then imagine it with lower shoulders (Fig. 3). That moves the free fingers even further forward, further unable to contact the substrate (despite the cheating on finger placement here by ignoring the configuration of the metacarpals). In any configuration the forelimbs were more like adult crutches on a little kid, my friends: very awkward on land. And, obviously, secondarily evolved, interrupted by a bipedal phase in pre-pterosaurs and basal pterosaurs. 

Walking pterosaur according to Bennett

Figure 3. Click to animate. Walking pterosaur according to Bennett (1997). Note the forelimbs provide no forward thrust, but merely act as props. They probably provided braking in this configuration and would have compressed (flexed) on contact with the substrate, rather than extending to provide thrust as in all other tetrapods. Compare this reconstruction to the Bennett reconstruction of Nyctosaurus.

Send alternatives if you have them!

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 1997. Terrestrial locomotion of pterosaurs: a reconstruction based on Pteraichnus trackways. Journal of Vertebrate Paleontology, 17: 104–113. online pdf
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D. 2010. In defence of parallel interphalangeal lines. Historical Biology 22:437-442.
Peters David 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos, 18: 2, 114 —141

Digitigrade Pterosaur Footprints

The Tradition
Based on known plantigrade and quadrupedal pterosaur tracks (Mazin et al. 1995, Lockley et al. 1995, and more below), ALL, yes, ALL pterosaurs must be considered plantigrade (flat-footed) and quadrupedal. No exceptions. And we are to ignore the widely held hypothesis that all traditional sisters, such as Scleromochlus and dinosaurs, were digitigrade (heels elevated), bipedal and lacked a large manual digit 4 and a large pedal digit 5.

Dimorphodon pes with shadows.

Figure 1. Dimorphodon pes with shadows. Pedal digit 5 can swing beneath the metatarsus. Note elevated proximal phalanges (Peters 2011). The weight of the animal is centered at the shoulder, which would have been over the toes, not the ankles. So there is no overwhelming pressure on the heel to collapse digit V.

The Heresy
According to Peters (2000, 2011) careful matching trackmakers to tracks reduces the clade of then (prior to 2009) known trackmakers to the Ornithocheiridae, the Ctenochasmatidae, the Azhdarchidae and the Pterodactylidae. All these pterosaurs shared a reduced pedal digit 5 and a plantigrade pes affirmed by parallel interphalangeal lines (PILs) analysis (Peters 2000, 2010). Based on CosesaurusRotodactylus (see below) and PIL analysis, basal fenestrasaurs and pterosaurs with an elongate pedal digit 5 (and several that did not) had a digitigrade pes with raised proximal phalanges with digit 5 impressing behind the others (Figs. 1, 2). Furthermore, new individual digitigrade footprints published in Peters (2011) can be matched to anurognathid and rhamphorhynchid pterosaurs (Figs. 3, 4). Digitigrade trackways are not yet known, other than Rotodactylus.

Cosesaurus and Rotodactylus, a perfect match.

Figure 2. Click to enlarge. Cosesaurus and Rotodactylus, a perfect match. Elevate the proximal phalanges along with the metatarsus, bend back digit 5 and Cosesaurus (left) fits perfectly into Rotodactylus (right).

Evidence for the Heresy
Little Cosesaurus aviceps nests here as a Middle Triassic sister to the ancestor of pterosaurs. Rotodactylus (Fig. 2) is an unusual Middle Triassic ichnite in which pedal digit 5 impresses far behind the other toes and digit 1 barely impresses. Put them together and you have a match in size and morphology.

Rotodactylus Trackmaker –
Not a Dinosaur Precursor

A recent paper by Brusatte et al. (2011) included several  Rotodactylus tracks and attributed them to a purported dinosaur precursor, LagerpetonUnfortunately no dinosaur precursors have digit 4 longer than 3 and Lagerpeton was not a dinosaur precursor. In any case, it is not likely that Lagerpeton made the tracks as digit 1 extended no further than metatarsal 2 and digit 5 could not reach the substrate. Cosesaurus was not considered as a potential trackmaker in Brusatte et al. (2011).

Digitigrade pterosaur tracks

Figure 3. A pterosaur pes belonging to a large anurognathid, "Dimorphodon weintraubi," alongside three digitigrade anurognathid tracks and a graphic representation of the phalanges within the "Sauria aberrante" track. Track D (Harris and Lacovara, 2004) a Late Jurassic anurognathid ichnite. Track C (Harris and Lacovara, 2004) a Late Jurassic anurognathid ichnite. ‘Sauria aberrante’ (MLP 61-IX-4-1; Casamiquela, 1962) an Early Jurassic anurognathid ichnite. Hypothetical phalanges drawn to match the Casamiquela (1962) ichnite. Note the impression of proximal phalanges in "Sauria aberrante" indicates the metatarsophalangeal joints were cylindrical enough to enable this, unlike the D. weintraubi pes. From Peters (2011).

Digitigrade Ichnites Matched to a Large Anurognathid Pterosaur
Three unidentified western hemisphere ichnites (Fig. 3) were published by Casamiquela (1962) and Harris and Lacovara (2004). All three most closely match a large Mexican anurognathid, “Dimorphodon” weintraubi. The four anterior digits diverged widely due to angled metatarsophalangeal joints. The presence of a digit 5 impression behind the others indicates these are fenestrasaurian in origin. D. weintraubi did not produce these tracks, but a sister pterosaur did. No other anurognathid and no other pterosaur is a closer match.

By the way, it is typical, but not necessary for digit 5 to make an impression in digitigrade pterosaur tracks. Simple extension of the proximal phalanx could elevate digit 5 from the substrate.

Pes of Rhamphorhynchus and matching track

Figure 4. Crayssac track different from all others. Inset: Pes of Rhamphorhynchus muensteri JME-SOS 4009, no. 62 in the Wellnhofer catalog

A Rhamphorhynchus Track
An unusual Crayssac track (Mazin et al. 1995) can be matched to a Rhamphorhynchus specimen. Not all Rhamphorhynchus pedes would match, but this one, JME-SOS 4009, no. 62 in the Wellnhofer catalog, is close.

For More Information
Please see this earlier blog on Bipedal vs. Quadrupedal Pterosaurs. See a selection of basal pterosaurs at reptileevolution.com. Or ask for a copy of Peters (2011).

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 1997a. The arboreal leaping theory of the origin of  pterosaur flight. Historical Biology, 123(4): 265–290.
Bennett SC 1997b. Terrestrial locomotion of pterosaurs: a reconstruction based on Pteraichnus trackways. Journal of Vertebrate Paleontology, 17: 104–113.
Brusatte SL, Niedzwiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B 278:1107-113. doi: 10.1098/rspb.2010.1746   online pdf
Casamiquela RM 1962. Sobre la pisada de un presunto sauria aberrante en el Liassico del Neuquen (Patagonia). Ameghiniana, 2(10): 183–186.
Chatterjee S and Templin RJ 2004. Posture, locomotion, and paleoecology of pterosaurs. The Geological Society of America Special Paper 376:1-63.
Clark, J, Hopson J, Hernandez R, Fastovsky D and Montellano M 1998. Foot posture in a primitive pterosaur. Nature 391: 886-889.
Lockley, MG, Logue TJ, Moratalla JJ, Hunt AJ, Schultz RJ. and Robinson JW 1995.The fossil trackway Pteraichnus is pterosaurian, not crocodilian; implications for the global distribution of pterosaur tracks. Ichnos 4: 7-20.
Mazin J-M, Hantzpergue P, Lafaurie G, and Vignaud P 1995. Des pistes de ptérosaures dans le Tithonien de Crayssac (Quercy, France). Comptes rendus de l’Academie des Sciences de Paris 321: 417-424.
Padian K 1983a. Osteology and functional morphology of Dimorphodon macronyx  (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum. Postilla, 189: 1–44.
Padian K 1983b. A functional analysis of flying and walking in pterosaurs. Paelobiology, 9: 218–239.
Padian K and Olsen P 1984. The fossil trackway Pteraichnus: Not pterosaurian, but crocodilian. Journal of Paleontology, 58: 178–184.
Padian K 2003. Pterosaur stance and gait and the interpretation of trackways. Ichnos, 10: 115–126.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7(1): 11­-41.
Peters D. 2010. In defence of parallel interphalangeal lines. Historical Biology 22:437-442.
Peters David 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos, 18: 2, 114 —141
Stokes WL 1957. Pterodactyl tracks from the Morrison Formation. Journal of Palaeontology 31: 952-954.
Unwin DM 1989. A predictive method for the identification of vertebrate ichnites and its application to pterosaur tracks. In Gillette, D. D. and Lockley, M. G.  (eds.) Dinosaur Tracks and Traces. Cambridge University Press, Cambridge. 259-274.
Unwin DM 1997. Pterosaur tracks and the terrestrial ability of pterosaurs. Lethaia 29: 373-386.


Pop Go the Poposaurs!

Updated April 22, 2014 as poposaurs now nest as basal archosaurs, not phytodinosaurs.

Poposaurus and the Poposauridae
Dr. Maurice G. Mehl (1915) described the very first poposaur, Poposaurus (Fig. 1), but it was based only on scraps. Even so, he was able to report, “Everything in the structure of the form so far studied indicates a well-muscled creature light in weight, possibly bipedal in gait occasionally, and most assuredly swift in movement.” Later, citing Nopcsa (1921, 1928), Colbert (1961) remarked, “[Poposaurus] has been commonly regarded as an ornithischian dinosaur of undoubted Triassic age.” In his conclusion Colbert (1961) considered Poposaurus particularly baffling before suggesting it was a theropod. More complete poposaurs would not be described until several decades later. A more complete Poposaurus would not be described until Gauthier et al. (2011) who nested Poposaurus as a “stem crocodilian”, between two sail-back archosaurs, Xilosuchus and Lotosaurus, close to rauisuchians plus crocodylomorphs.

The Poposauridae: The Traditional List
According to Nesbitt (2011) and Gauthier et al. (2011) other poposaurs include Qianosuchus, Arizonasaurus, Xilosuchus, Lotosaurus, Sillosuchus, Shuvosaurus and Effigia. This clade nested as sisters to the Rauisuchia + Crocodylomorpha. Outgroup taxa included Gracilisuchus, Turfanosuchus, Ticinosuchus, Revueltosaurus and the Aetosauria.

The Poposauridae: The Heretical List
Here only the following taxa nested as poposaurs: Poposaurus,  ShuvosaurusEffigia, Turfanosuchus, Silesaurus and Lotosaurus. See figure 1.

Figure 1. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

Figure 1. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

 

Dino-Like Crocs? Or Dinos with an Ankle Issue?
Poposaurs are widely considered to be dinosaur-like crocs, nesting with the Rauisuchia + Crocodylomorpha. In particular, Effigia (Fig. 1) was considered to exhibit “extreme convergence” with the body plan of dinosaurs (Nesbitt and Norell 2006).

By contrast, the present large reptile study, many times larger than the Gauthier (2011) or Nesbitt (2011) studies, found that poposaurs nested as basal archosaurs derived from as sited to Turfanosuchus. That solves all sorts of problems. The problem with earlier studies stemmed from a lack of considering the possibility of convergence in these clades with regard to the development of the calcaneal tuber, which also developed by convergence in the unrelated phytosaurs and to a lesser extent in chanaresuchids, including Lagerpeton, which we looked at earlier.

Chatterjee (1985) coined Rauisuchia to incorporate Rauisuchidae and Poposauridae. That term definition is retained here, so birds and crocs are also members of the Rauisuchia. Benton and Clark (1988) used Prestosuchus and Ticinosuchus to represent Rauisuchidae and Postosuchus to represent the Poposauridae. Nesbitt (2011) considered poposaurs monophyletic and a clade within the rauisuchians.

The Postosuchus Pelvis Problem
Postosuchus
was considered a poposaurid by several writers, based largely on the pelvis presented by Chatterjee (1985). Long and Murray (1995) showed that that pelvis did not belong to Postosuchus but to an unidentified poposaurid, hence the confusion.

Was Poposaurus an herbivore?
Poposaurus had tiny and gracile fingers with tiny unguals on a short arm, so it was not grasping prey. Rather this clue suggests herbivory as in all other poposaurs. The cervicals were more robust. The vertebral spines were all higher and expanded anteroposteriorly. The tail was deeper proximally and longer distally. The ilium extended over the femur in the manner of a rauisuchian pelvis for additional support. The pubis was longer than the femur. A calcaneal spur or tuber developed extending posterodorsally.

Shuvosaurus and Effigia were more gracile overall with a smaller, toothless skull. The scapula was more robust. The toes were more slender, but the toe unguals were larger.

Silesaurus had a smaller skull on an elongated neck. The torso was relatively smaller and the legs were relatively longer. Lotosaurus became secondarily quadrupedal with a larger body, shorter neck and a dorsal sail supported by neural spines.

Summary
Poposaurs developed early into a variety of niches. Some had a slender build and a bipedal configuration with an elongated neck and an herbivorous or toothless dentition. A calcaneal spur developed in this clade convergent with the situation in derived rauisuchians, which were also heavily built, short-legged bipeds, and in crocodylomorphs as they became quadrupeds. The longer-legged poposaurids had smaller spurs. Poposauridae was a monophyletic clade that did not survive into the Jurassic.


References
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Casamiquela RM 1967. Un nuevo dinosaurio ornitisquio triásico (Pisanosaurus mertii; Ornithopoda) de la Formación Ischigualasto, Argentina. Ameghiniana 4 (2): 47–64.
Colbert EH 1961. The Triassic Reptile, Poposaurus. Fieldiana 14(4):59-78. online pdf
Dzik J 2003. A beaked herbivorous archosaur with dinosaur affinities from the early Late Triassic of Poland. Journal of Vertebrate Paleontology 23: 556-574.
Gauthier JA, Nesbitt SJ, Schachner ER, Bever GS and Joyce WG 2011. The bipedal stem crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion. Bulletin of the Peabody Museum of Natural History 52:107-126.
Hunt AP 1989. A new ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. In Lucas, S. G. and A. P. Hunt (Eds.), Dawn of the age of dinosaurs in the American Southwest 355–358.
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Mehl MG 1915. Poposaurus gracilis, a new reptile from the Triassic of Wyoming. Journal of Geology 23:516–522.
Nesbitt SJ 2003. Arizonasaurus and its implications for archosaur divergence
Sterling J. Nesbitt Proceedings of the Royal Society, London B (Suppl.) 270, S234–S237. DOI 10.1098/rsbl.2003.0066
Nesbitt SJ and Norell MA 2006. Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society B 273:1045–1048. online
Nesbitt S 2007. The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. Bulletin of the American Museum of Natural History, 302: 84 pp. online pdf
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218
Nopcsa, F von 1921. Zur systematischen Stellung von Poposaurus (Mehl). Zentralbl. Min. Geol. Paleont., p. 348.
Nopcsa, F von 1928. The genera of reptiles. Palaeobiologica, 1, pp. 163-188.
Parker WG., et al. 2005. The Pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. In Proceedings of the Royal Society London B 272(1566):963–969.
Weinbaum JC and Hungerbuhler A 2007. A Revision of Poposaurus gracilis (Archosauria: Suchia) based on two new specimens from the Late Triassic of the southwestern USA. Palaeontologische Zeitschrift 81(2):131-145.
Zhang F-K 1975. A new thecodont Lotosaurus, from Middle Triassic of Hunan. Vertebrata PalAsiatica 13:144-147.

AMNH Effigia webpage
wiki/Effigia
wiki/Lotosaurus
wiki/Pisanosaurus
wiki/Poposaurus
wiki/Revueltosaurus
wiki/Silesaurus

What is Lagerpeton? The Heretical View.

Lagerpeton chanarensis (Romer 1971) Middle Triassic, ~ 240 mya, ~0.7 meters long (Fig. 1) was originally and traditionally considered a dinosauromorph, like Marasuchus. For several decades it has played a pivotal role in traditional dinosaur evolution studies, nesting at the base of the Dinosauria along with pterosaurs, which were considered and dismissed here earlier.

Lagerpeton reconstructed.

Figure 1. Lagerpeton reconstructed.

Only the hindlimb and a portion of the lumbar and caudal regions of the vertebral series in Lagerpeton have been found. That makes it something of an enigma wondering what the rest of it looked like. The pedal proportions don’t match those of pterosaurs or Marasuchus. Neither does the pelvis. The rise in the astragalocalcaneum occurs behind the tibia/fibula, not in front, as in Marasuchus and dinosaurs.

Dromomeron
Recently a femur described by Irmis et al. (2007) and Nesbitt et al. (2009) as a sister to Lagerpeton was named DromomeronIt’s a pretty good match. However, in those studies, pterosaurs and both of these lagerpetids were found to be derived from parasuchians, like Parasuchus, which are almost polar opposites in terms of morphology. Such mismatches should raise a red flag that a problem is present in the matrix of data.

Boy It Would Be Great If We Only Had a Skull!
So what is Lagerpeton, if not a sister to dinosaurs, phytosaurs and pterosaurs? Given all the reptiles now know, what would be its closest match? Ideally it would be great to find a specimen with more of the skeleton preserved. Well that has already happened with little to no fanfare.

 

Figure 2. A specimen Bonaparte attributed to Tropidosuchus, but it is also a sister to Lagerpeton

Figure 2. A specimen Bonaparte attributed to Tropidosuchus, but it is also a sister to Lagerpeton. The foot is distinct in this specimen from the Tropidosauchus holotype. Like Lagerpeton, metatarsal 4 is not more gracile than mc3.

A Specimen Attributed to Tropidosuchus
In his book, Dinosaurios de America del Sur, Bonaparte (1994) included a photograph of a nearly complete and articulated specimen attributed to Tropidosuchus. That specimen has not been described yet. Interestingly the pes (Fig. 2) shares more traits with Lagerpeton, which also has an elongated metatarsal 4.

The specimen attributed to Tropidosuchus by Bonaparte 1994.

Figure 3. The specimen attributed to Tropidosuchus by Bonaparte 1994.

The Chanaresuchids
 Chanaresuchus (Figure 4).  Cerritosaurus was a sister to their common ancestor. The BPI 2871 specimen attributed to Youngina by Gow (1974) also nested here. It is currently under study by an unknown worker, so we should be hearing some news about this specimen soon. It was not illustrated with an antorbital fenestra (AOF) and fossa, but I suspect it had one considering the small size of the AOF in its sisters.

Chanaresuchids to scale, including Tropidosuchus and Lagerpeton.

Figure 4. Chanaresuchids to scale, including Tropidosuchus and Lagerpeton. Click to enlarge. The inclusion of BPI 2871 here is an error. It belongs with other Youngina/Youngoides specimens at the base of the Archosauriformes, but isn’t it an interesting convergence with this taxa?

In the chanaresuchid clade the pedal digits did not share many traits with dinosaurs. The pelvis was distinct as well. The reason why parasuchians and phytosaurs nested with pterosaurs and dinosaurs in prior studies seems to be largely due to the inclusion of Lagerpeton and the exclusion of Cerritosaurus, Doswellia and the Choristodera. In a larger study including all these taxa and many more (see below), these problems become fully resolved and all nested sisters more closely resemble each other in whole and in detail.

The Pseudarchosauriformes. Lagerpeton is the most derived taxon.

Figure 5. The Pararchosauriformes. Lagerpeton is the most derived taxon. Click to see entire tree.

The Pararchosauriformes
The large reptile tree not only split the reptiles into two distinct clades. It also split the archosauriformes. On one branch are the Euarchosauriformes from Proterosuchus to birds and crocs. On the other branch are the Pararchosauriformes from the RC 91 specimen of Youngoides to Lagerpeton. This clade also includes choristoderes, Proterochampsa, phytosaurs and chanaresuchids, taxa largely united by a long snout with dorsal nares. An antorbital fenestra appeared in derived members of this clade by convergence with the Euarchosauriformes.

So…
Lagerpeton nests with Tropidosuchus, Chanaresuchus and Cerritosaurus in order of increasing distance. Lagerpeton does share a common ancestor with dinosaurs, but it goes all the way back to basal Youngina. Lagerpeton does share a common ancestor with pterosaurs, but it goes all the way back to Cephalerpeton, the most primitive known reptile.

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
Bonaparte JF 1994. Dinosaurios de America del Sur. Impreso en Artes Gráficas Sagitario. Buenes Aires. 174pp. ISBN: 9504368581
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218.
Romer AS 1971 The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria, n. 378, p. 1-10.
Sereno PC and Arcucci AB 1993. Dinosaurian precursors from the Middle Triassic of Argentina: Lagerpeton chanarensis. Journal of Vertebrate Paleontology, 13, 385–399.

wiki/Lagerpeton

What is Scleromochlus?

Scleromochlus taylori was a little reptilian biped from the Late Triassic of Scotland. The several fossils that are known are preserved as crushed impressions in sandstone. The long legs and slender arms of Scleromochlus immediately set it apart as something very special.

Scleromochlus, a basal crocodylomorph

Figure 1. Scleromochlus, a basal crocodylomorph. That's a sister taxon, Gracilisuchus in the upper right hand corner.

Early Assignments
Woodward (1909) first described Scleromochlus taylori as a dinosaur. Von Huene (1914) reassigned it to the Pseudosuchia. Padian (1984) considered it an Ornithodiran, allied to both pterosaurs and dinosaurs. Sereno (1991) considered it a sister to pterosaurs. Padian (1997) named the clade containing Scleromochlus and pterosaurs the Pterosauromorpha. Benton (1999) used 16 taxa to determine that Scleromochlus was basal to pterosaurs, Lagerpeton, Lagosuchus (Marasuchus) and the Dinosauria. Phytosaurs and Proterochampsa were outgroups. Bipedal crocs were not included.

With Pterosaurs? And Phytosaurs?
The absurdity of these nestings were discussed in an earlier 3-part blog. The linking of Scleromochlus with pterosaurs is also embarrassing. Scleromochlus had tiny fingers, a terminal naris, a deep antorbital fossa, too few cervicals, too deep chevrons and no pedal digit 5, among several other discrediting traits. Cosesaurus is a much better pterosaur sister. It was similar in size to Scleromochlus and had a pteroid, prepubis, extradermal membranes, a long fifth toe, a long fourth finger and other traits shared with pterosaurs. Terrestrisuchus is a much better sister to Scleromochlus (Figure 3).

Properly Nesting Scleromochlus
The present large study demonstrates that pterosaurs and Scleromochlus were not closely related. Even turtles nest closer to pterosaurs than Scleromochlus would. Here Scleromochlus nests within the base of the Crocodylomorpha close to Terrestrisuchus, Saltopus and Gracilisuchus. Surprisingly, no one but Peters (2002) has considered Scleromochlus a crocodylomorph (see Wiki links below) despite the obvious similarities (Figure 3).

Benton’s Biased Reconstruction
Benton (1997) reconstructed Scleromochlus with a posterior-leaning quadrate, as in pterosaurs, but there is no evidence for this. In doing so, Benton reconstructed the skull with a hyper-extended retroarticular process with a quadrate articulation nowhere near the articular bone. The Scleromochlus skull is much wider than tall and the many samples were crushed dorsoventrally, obliterating any data on the orientation of the quadrate. Given an alternate anterior leaning quadrate (Figure 1) the problem with the retroarticular process is removed.

 Scleromochlus according to Benton (1999).

Figure 2. Scleromochlus according to Benton (1999). Red arrows and captions indicate dissimilarities with pterosaurs.

Terrestrisuchus, Gracilisuchus and Saltopus as Sister Taxa
A comparison with Terrestrisuchus, Gracilisuchus and Saltopus is instructive. Each had been considered bipedal. Each had a small upright scapula, a reduced calcaneum and an elongated, appressed metatarsus. Gracilisuchus shared robust cervical ribs, a lumbar region, a short tail and a flat-topped ilium. The palate configuration was virtually identical. Saltopus had tiny fingers, more than two sacral vertebrae, a longer tibia than femur and an elongated hind limb. Benton and Walker (2011) apparently misinterpreted the ephemeral sacrals of Saltopus by deciding that only two were present and elongating each one twice as long as proximal dorsals and caudals, unlike the situation in its other sisters. Terrestrisuchus had a smaller skull and longer neck, but was otherwise virtually identical to Scleromochlus.

Basal Crocodylomorpha

Figure 3. Basal Crocodylomorpha, including Gracilisuchus, Saltopus, Scleromochlus and Terrestrisuchus

Scleromochlus taylori (Woodward 1907) Late Carnian, Late Triassic ~217 mya, 18 cm long, was derived from a sister to DecuriasuchusLewisuchus and Pseudhesperosuchus at the base of a clade that included the crocodylomorphs Gracilisuchus, Saltopus and  Terrestrisuchus. Read more about Scleromochlus here.

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 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoolological Journal of the Linnean Society 118: 261–308.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Benton MJ and Clark JM 1988. Archosaur phylogeny and the relationships of the Crocodilia in MJ Benton (ed.), The Phylogeny and Classification of the Tetrapods 1: 295-338. Oxford, The Systematics Association.
Benton MJ and Walker AD 2011. Saltopus, a dinosauriform from the Upper Triassic of Scotland. Earth and Environmental Science Transactions of the Royal Society of Edinburgh: 101 (Special Issue 3-4):285-299. DOI:10.1017/S1755691011020081
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.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Huene FR 1910. Ein primitiver Dinosaurier aus der mittleren Trias von Elgin. Geol. Pal. Abh. n. s., 8:315-322.
Juul L 1994. The phylogeny of basal archosaurs. Palaeontographica africana 1994: 1-38.
Padian K. 1984. The Origin of Pterosaurs. Proceedings, Third Symposium on Mesozoic Terrestrial Ecosystems, Tubingen 1984. Online pdf
Parrish JM 1993. Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly. Journal of Vertebrate Paleontology 13(3):287-308.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Hist Bio 15: 277–301.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology 11 (Supplement) Memoire 2: 1–53.
Woodward AS 1907. On a new dinosaurian reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society 1907 63:140-144.

wiki/Gracilisuchus
wiki/Saltopus
wiki/Scleromochlus
wiki/Terrestrisuchus

What is Lanthanolania?

Here’s another case of an inadequately small inclusion set mistakenly nesting a taxon far from its most parsimonious nesting site. Today we look at Lanthanolania, described earlier (Modesto and Reisz 2002) as a sister to Planocephalus, and recently (Reisz and Modesto 2011) as a sister to Orovenator (Figure 1). New postcranial material (which has not yet been published) sets it apart as the oldest known bipedal diapsid.

Lanthanolania and its sisters.

Figure 1. Lanthanolania and its sisters. Orovenator does not belong.

Lanthanolania ivakhnenkoi (Modesto and Reisz 2003) Late Permian ~265 mya ~2.5cm skull length was originally considered a sister to Planocephalosaurus and the Squamata. A more recent analysis by Reisz and Modesto (2011), that included nearly a complete post cranial skeleton, nested Lanthanolania with the younginid, Orovenator. I haven’t seen their analysis, but the present analysis nests Lanthanolania with the gliding lepidosauromorphs, CoelurosauravusIcarosaurus, and Kuehneosaurus, close to Saurosternon and Palaegama, with which it was not previously tested against. Moving Lanthanolania close to Orovenator added a minimum of 20 steps.

Distinct from Palaegama, the skull of Lanthanolania was relatively shorter with a taller orbit.  The rostrum was convex and the ascending process of the maxilla expanded dorsally. The lacrimal was larger. The postorbital was larger. The palate was nearly identical to that of Kuehneosaurus. The skull in ventral view was also similar in shape.

Limb proportions mentioned by Reisz and Modesto (2011) suggest Lanthanolania might have been the oldest known bipedal diapsid. Unfortunately Lanthanolania was not a diapsid (taxa related to Petrolacosaurus) and Eudibamus, a true diapsid, is 25 million years older (if it was a biped as often described). On the other hand, two Lanthanolania sister taxa, Palaegama and Saurosternon, both have proportions similar to those of bipedal lizards. I am eager to see the post-crania of Lanthanolania to see if there are any clues in the ribs. pelvis and feet demonstrating affinity to the Triassic gliders.

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:
Modesto SP and Reisz RR 2003. An enigmatic new diapsid reptile from the Upper Permian of Eastern Europe. Journal of Vertebrate Paleontology 22 (4): 851-855.
Reisz RR and Modesto SP 2011. The neodiapsid Lanthanolania ivakhnenkoi from the Middle Permian of Russia, and the initial diversification of diapsid reptiles.SVPCA abstract published online.

The Origin of the Pterosaur Sternal Complex

It is a common and mistaken paradigm that pterosaurs appeared out of nowhere, seemingly unrelated to other prehistoric reptiles. Those who say this (and the list is long) also judiciously avoid any discussions of pterosaurs as lizards or fenestrasaurs. Their investments in the outmoded and unsupportable archosaur hypothesis have not provided answers — and never will. Here we will take a look at the development of the sternal complex of pterosaurs evolving from the most parsimonious sister taxa yet discovered (Peters 2000a, 2007).

The Pectoral Girdle in Huehuecuetzpalli
The story begins with Huehuecuetzpalli (Reynoso 1998), a basal tritosaurid lizard with a fairly typical pectoral girdle (Figure 1). A T-shaped interclavicle and sinuous tapered clavicles anteriorly framed the short scapula and fenestrated but otherwise discoidal coracoid. A broad sternum was located at the posterior tip of the interclavicle. The coracoid was free to rotate between the clavicles, interclavicle and sternum, increasing the range of motion of the humerus.

The Pectoral Girdle in Cosesaurus
Several changes to this pattern can be seen in the basal fenestrasaur and tritosaur, Cosesaurus (Figure 1). The interclavicle developed an anterior process. The sternum moved anteriorly, now dorsal to the transverse processes of the interclavicle. The clavicles were shorter, no wider than the sternum and aligned with the anterior rim of the sternum. The coracoids were relatively larger and considerably narrower as the anterior fenestrations expanded until just the quadrant-shaped posterior rim remained. The scapula was strap-shaped with a long posterior process extending over several more dorsal ribs. With the sternum leading edge now anterior to the interclavicle trailing edge, the coracoids had no room to move and their ventral stems became socketed and essentially immobile, resembling the configuration in birds and serving as a precursor to the configuration in pterosaurs.

 

Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

Figure 3. Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex. Figure 1. The evolution of the pterosaur pectoral girdle and sternal complex featuring Huehuecuetzpalli, Cosesaurus, Longisquama, and the basal pterosaur, MPUM 6009.

The Pectoral Girdle in Longisquama
In Longsiquama (Figure 1) the interclavicle, clavicles and sternum are closely integrated, as in pterosaurs. Distinct from all other tetrapods, the clavicles curved posteriorly, extending to the posterior rim of the crescent-shaped sternum, which they frame. The cruciform interclavicle extended ventrally to form a small keel. Taphonomically displaced to beneath the throat, the overlapping clavicles were mistaken by Jones et al. (2000) for a bird-like furcula (fused clavicles in birds).

The Pectoral Girdle in Pterosaurs
In basal pterosaurs (Figure 1) there were few changes from the Longisquama pattern. So the sternal complex (Wild 1994), like many other aspects of pterosaur morphology, had evolved before the advent of large pterosaurian wings (Peters 2002, contra Bennett 2008).

Summary
All these changes could never have taken place if Cosesaurus was restricted to a typical quadrupedal configuration. The forelimbs had to become elevated from the substrate in a bipedal configuration, as imagined (based on morphology) in its phylogenetic predecessors, Lacertulus (Carroll and Thompson 1982) and Huehuecuetzpalli — and as evidence by matching Cosesaurus pedes to Rotodactylus tracks (Peters 2000b) which were ocassionally bipedal. Cosesaurus had a pectoral complex essentially and mechanically identical to that of pterosaurs (and broadly similar to that of birds). So it seems likely that it was also flapping, probably in some sort of territorial or mating ritual, long before gliding and flying were possible in its descendant taxa, Sharovipteryx, Longisquama and 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:
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.
Carroll and Thompson 1982. A bipedal lizardlike reptile fro the Karroo. Journal of Palaeontology 56:1-10.
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.
Peters D 2000a. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2000b. 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 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.

The Prepubis of Pterosaurs (and Fenestrasaurs)

Formerly the Prepubis was Found Only in Pterosaurs
Only a few years ago it seemed that pterosaurs had three bones not found in other tetrapods: the prepubis, the pteroid and the preaxial carpal. Now these bones have been found in three fenestrasaur sister taxa, with Peters (2009) reporting on the latter two. Unfortunately, manuscripts reporting the appearance of the prepubis in Longisquama, Sharovipteryx and Cosesaurus were blackballed during the review process on claims that I used photographs. Well, they’re still the best way to share data (Figure 1) and review old errors (see below).

Cosesaurus prepubis

Figure 1. Cosesaurus prepubis in situ and reconstructed.

In tiny Cosesaurus (Figure 1), the first known prepubis measured only 3 mm in length. In Peters (2000) I didn’t recognize the prepubes when I first saw them, opting instead to describe the ilium anterior process with its own anterior process, following Ellenberger (1978, 1993), who did the same. That “process” was really the stem of the prepubis with the fan portion coincident with the broad, flat anterior process of the ilium. The other matching prepubis was largely beneath the right femur.

The pelvis and prepubes of Sharovipteryx.

Figure 2. The pelvis and prepubes of Sharovipteryx.

I presented the prepubes of Sharovipteryx during a podium session at the meeting of the Society of Vertebrate Paleontology in 2003. In Sharovipteryx both prepubes are readily visible. Unfortunately no one bothered to look for them, or map them, before. Click here to see a rollover image of the fossil and its interpretation.

In Longisquama I only found one prepubis and it was right at the edge of the rock break. The other one may have been a wee bit beyond. Click here to see the in situ fossil and its interpretation.

By convergence, basal mammals, like the opossum and platypus, have prepubes (known as marsupial or epipubic bones), which are used to support the marsupium, or pouch. There is no reason to believe that pterosaurs had marsupial pouches since they were lizards that layed full term eggs. Certain ornithischian dinosaurs had a prepubic process and crocodilians have a hinged pubis, otherwise similar in appearance to the prepubis of pterosaurs.

Why Develop a Prepubis?
In many respects the prepubis of fenestrasaurs resembled a miniaturized version of the booted pubis in Postosuchus, Herrerasaurus and Tyrannosaurus and likely served the same purpose, as an aid in locomotion. In Cosesaurus the prepubis was a novel ossification, extending ventrally from the pubis and no doubt anchored muscles of adduction, pulling the femora in toward the midline. In Pteranodon the prepubis fused to its counterpart and the posterior gastralia, but such fusion is not found in most other pterosaurs. Even so, the prepubis does appear to also enhance the function of the gastralia in support of the lower torso.

Figure 3. The pelvis (in tints of gray) and prepubis (in orange) of several tritosaurs, fenestrasaurs and pterosaurs. Arrow points to the anterior.

Figure 3. The pelvis (in tints of gray) and prepubis (in orange) of several tritosaurs, fenestrasaurs and pterosaurs. Arrow points to the anterior.

The Prepubis as Part of the Pelvis
The anterior and posterior expansion of the ilium and the infilling of the thyroid fenestra are gradually evolving traits in basal tritosaurs. The prepubis appeared when the anterior process of the ilium became hyper-elongated in Cosesaurus, and so was likely related to bipedalism. The feet of Cosesaurus have been matched to occasionally bipedal and narrow-gauge Triassic tracks within the ichnogenus, Rotodactylus (Peters 2000) and the anterior extension of the ilium is a hallmark of bipedalism in lizards (Snyder 1954) and dinosaurs.

Sister taxa more primitive than Cosesaurus had only two sacral vertebrae, an unfused ventral pelvis and short ilia. The fenestrasaurs, including Cosesaurus and basal pterosaurs, had four or more sacral vertebrae, a fused puboischiadic plate and elongated ilia, plus a prepubis — all of which served to increase and elongate the lateral surfaces of the pelvis.

The prepubes were more or less aligned with the femora when standing bipedally. In this configuration they served as anchors for femoral adduction (keeping the knees from sprawling too much). In addition, these pelvic surfaces likely anchored more extensive rotator femoral muscles because the femoral retractors were concurrently shrinking, judging by the reduction of the transverse processes and chevrons of the increasingly attenuated tail.

The Prepubis as Part of the Gastralia
Gastralia are not observable in Huehuecuetzpalli. They are barely visible to lightly present in Macrocnemus and Langobardisaurus. In Cosesaurus and pterosaurs robust gastralia span the gap between the sternal complex  and prepubis. As in other tetrapods, gastralia would have stiffened the belly adding ventral support in a bipedal configuration. Such support would have had been useful to counter the long moment arm that would have developed at the posterior dorsal vertebrae with the fulcrum at the acetabulum whenever the hind limbs supported all the weight.

Prepubis Orientation and Movement
Claessens et al. (2009) imagined the prepubis oriented in line with the gastralia, but that is false (Figure 3). They imagined it able to rotate at its base to facilitate respiration, but that is also false. They mistakenly compared pterosaurs to archosaurs (birds and crocs). They imagined a prepubis for Anhanguera, which is probably true, but none was preserved.

In their best prepubis example, a Rhamphorhynchus specimen (MB-R. 3633.1-2), Claessens et al. (2009) considered the prepubis to be articulated to the pubis with a moveable joint and with its major axis in line with the gastralia. The prepubis was correctly identified, but Claessens et al. (2009) failed to notice it had been rotated more than 90 degrees posteriorly during taphonomy such that the hollow cylindrical stem moved into the plane of the gastralia with its pubic articulation open anteriorly. The actual prong-like anterior process of the prepubis is visible ventral to the pubis. The ventral prong continues largely hidden beneath the pelvis. Properly rotated and configured like that of other fenestrasaurs, including other pterosaurs, the prepubis actually deepens the torso.

A Respiration Function for Prepubes?
Claessens et al. (2009) sought to demonstrate ventral expansion of the pterosaur abdomen to facilitate respiration via “caudoventral rotation of the prepubis.”  Unfortunately they misoriented the prepubis. Correctly configured, the proposed “caudoventral rotation at the pubis prepubis joint” could only stretch the gastralia away from the sternal complex (IF it was mobile), not ventrally expand the torso.

Perhaps more importantly, the actual pubis-prepubis joint is actually flat, or slightly, expanded, preventing caudoventral rotation. It’s a butt joint. To that point, in Claessens et al. (2009, fig. 3b) the prepubis of Pteranodon was correctly figured (extending ventrally from the pubis) and their own figure demonstrates torso expansion during respiration without prepubis rotation.

Variation in Prepubes
The shape and size of the prepubis is fenestrasaurs varied greatly. In certain Campylognathoides the prepubes are relatively large, fan-like and perforated. In Dorygnathus and basal ornithocheirids the prepubes were larger and longer than the shortened pubes. In a derived ornithocheird the prepubes were quite tiny. In Nyctosaurus and several other pterosaurs, like Rhamphorhyrnchus, the perforation expanded beyond the anterior margin of the prepubis, creating a “fork” ventrally with one prong contacting the posterior gastralium and the other prong articulating and sometimes fusing with its symmetrical counterpart.

In Summary
The prepubis has been largely ignored in pterosaur studies. It first appeared in basal fenestrasaurs. It was immobile, acting like an extension of the pubis.  It’s use was in locomotion and ventral support during bipedal excursions. The shape of the prepubis, while difficult to quantify, is distinct for every genus.

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:
Claessens LPAM, O’Connor,PM, Unwin DM 2009. Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism. PLoS ONE 4(2):e4497. online PLOS paper.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Snyder RC 1954. The anatomy and function of the pelvic girdle and hind limb in lizard locomotion. American Journal of Anatomy 95:1-46.

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.