The antorbital and lateral temporal fenestrae of the frog , Rana

Earlier we looked at the evolution of the frog, Rana. And it continues to be the most popular blog post of the past year.

Today, after adding Rana to the matrix of the large reptile tree (still not updated), I think it’s time we looked at the antorbital fenestra of Rana, and the lateral temporal fenestra as well (Fig. 1).

Figure 1. Rana, the bull frog, with naris in red, orbit in purple, antorbital fenestra in dark blue and lateral temporal fenestra in orange. The reduction of the the skull bones in Rana created these fenestrae.

Figure 1. Rana, the bull frog, with naris in red, orbit in purple, antorbital fenestra in dark blue and lateral temporal fenestra in orange. The reduction of the the skull bones in Rana created these fenestrae.

One usually thinks of additional skull fenestrae in the province of reptiles. As we saw earlier, the antorbital fenestra comes and goes in several reptiles. So does the lateral temporal fenestra. Amphibians (non-amniote tetrapods) typically do not have skull fenestrae. Neither to most basal reptiles.

Relative to the body, the skull of Rana is enormous. So are the hind limbs. Frogs leap, as everyone knows, and if the skull is going to be large it also has to be lightweight to enable longer leaps. So the skull bones are reduced to their bare minimum creating fenestrae.

Proximal outgroup taxa, including long-legged Triadobatrachus, likewise have reduced skull bones.

More distant outgroup taxa, including short-legged Gerobatrachaus and Doleserpeton and Utegenia have relatively smaller skulls and shorter hind limbs — and no skull fenestrae.

 

 

Youngoides minor RC91- better data

For decades the only published view of the RC91 specimen of Youngoides minor (Broom and Robinson 1948, Late Permian) was their published drawing (Fig. 1).

Figure 1. Youngoides minor RC91 by Broom and Robinson 1924.

Figure 1. Youngoides minor RC91 by Broom and Robinson 1924.

This is a pretty good reconstruction for the fossil, which is broken lengthwise between the dorsal and ventral portions (Fig. 2, images courtesy of Bruce Rubidge).

Figure 2. Youngoides minor RC91 in dorsal and ventral views. Yes, the left side is folded on itself.

Figure 2. Youngoides minor RC91 in dorsal and ventral views. Yes, the left side is folded on itself.

Given these two images, you might think they were two different fossils, but actually the ventral portion is folded back at right angles beneath the dorsal portion.

Figure 3. Youngoides minor RC91 digitally colorized.

Figure 3. Youngoides minor RC91 digitally colorized.

Here (Fig. 3) DGS helps identify the various bits and pieces.

Figure 4. Youngoides minor RC91 reconstructed.

Figure 4. Youngoides minor RC91 reconstructed.

A reconstruction (Fig. 4) puts it all together. The phylogenetic placement did not change with the additional data.

Lower and wider than other specimens named Youngoides, RC91 was derived from a sister to the RC90 specimen of Youngina and was basal to the AMNH 5561 specimen of Youngina. The skull of the RC91 specimen of Youngoides minor has slightly constricted rostrum in dorsal view. The jawline is convex. The orbit enters the anterior half of the skull. The supratemporal and postorbital contact and the posterior jugal descends. It is among the smallest specimens. And, yes, that is a nascent antorbital fenestra.

References
Broom R and Robinson JT 1948. Some new fossil reptiles from the Karroo beds of South Africa: Proceedings of the Zoological Society of London, series B, v. 118, p. 392-407.

wiki/Youngina

RC = Rubidge Collection, Wellwood, Graaff Reinet, South Africa.

 

 

Another lizard with an antorbital fenestra!

Earlier we looked at the nesting of pterosaurs within a third clade of lepidosaurs (lizards), the Tritosauria, outside of the Squamata (Iguania + Scleroglossa). Pterosaurs, as everyone knows, have an antorbital fenestra. That’s the principal reason why most pterosaur workers try to force fit them into the Archosauria.

The frilled lizard, Chlamydosaurus kingii, is famous for many things: bipedal walking, frilled neck skin and that cantankerous attitude. Now let’s add: antorbital fenestra (Fig.1). This is the only living lizard that I know of (there may be more!) that has an antorbital fenestra. That makes six non-homologous appearances in the Reptilia. Here and here are the other five.

Figure 1. Frilled lizard skeleton. Note the small skull opening between the naris and orbit. That's an antorbital fenestra.

Figure 1. Frilled lizard skeleton. Click to enlarge. Note the small skull opening between the naris and orbit. That’s an antorbital fenestra. And this one raises the total of distinct non-homologous antorbital fenestra to six and the second among lepidosaurs. Fenestrasaurs were the first. Drepanosaurs may be homologous with Jesairosaurus at the base.

With its bowed hind limbs
The frilled lizard presents a good analog for how bowlegged pterosaurs (chiefly derived forms) would have run bipedally, perhaps prior to flight. This is the first time I’ve seen a skeleton of Chlamydosaurus, having featured this lizard in an early paper (Peters 2000) as an example of a reptile capable of bipedal locomotion, convergent with fenestrasaurs. I am pleased to note the ilium of Chlamydosaurus has a small anterior process (a hallmark of bipedal reptiles, exaggerated in fenestrasaurs, including pterosaurs). The tail, with those deep chevrons and wide transverse processes, would have been more robust than in any fenestrasaur. The closely apprssed tibia and fibula are also cursor traits. The asymmetric foot is no impediment to bipedal locomotion, contra the opinion of many pterosaur workers.

That antorbital fenestra has an unknown (to me) function. If anyone has that data, please let me know.

Added note: Darren Naish was kind enough to refer me to other lizards with this sort of antorbital fenestra, Pogona vitticeps, the bearded lizard is one, and here is a Digimorph link to it. A quick Googling revealed that the Harderian gland is located at the medial corner of the orbit. The lacrimal gland is smaller and appears at the posterior eyelids. According to Wikipedia, “The Harderian gland is a gland found within the eye’s orbit which occurs in tetrapods (reptiles, amphibians, birds and mammals) that possess a nictitating membrane and the fluid it secretes (mucous, serous or lipid) varies between different groups of animals.”

And how about that retroarticular process~! Perhaps related to the neck frill. I understand not all of the bones of the frill are included here.

The frilled lizard can be seen in action here on YouTube.

More on bipedal pterosaur tracks here.

References
This image (Fig. 1) comes from taxidermy.net. There are several more images of Chlamydosaurus from other angles there.

Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

A closer look at the “antorbital fossa” in two pterosaurs, Raeticodactylus and Dimorphodon

Nesbitt and Hone (2010) broke with tradition to propose that certain pterosaurs had a mandibular fenestra. We discussed this mistake earlier. Now we are going to look at another one of their other futile grasps at the archosaur straw, a purported antorbital fossa in Dimorphodon (Figs. 1, 2) and Raeticodactylus (Fig. 3). An antorbital fossa is not found in ANY other pterosaur. And the two examples they propose don’t match each other in any way or fashion. So, ironically, Nesbitt and Hone (2010) were acting as heretics and I am here to hold the traditional line.

From Nesbitt and HONE 2010, a purported antorbital fossa in Dimorphodon. Note where it is. This strut support is a little thinner and therefore a little deeper than the rest of the ascending process. Dimorphodon depresses this area more than other pterosaurs.

Figure 1. From Nesbitt and Hone 2010, a purported antorbital fossa in Dimorphodon. Note where it is compared to figure 3 (below). This triangular strut support is a little thinner and therefore a little deeper than the rest of the cylindrical ascending process. Dimorphodon depresses this area more than other pterosaurs, like Eudimorphodon.  This also may be due to crushing, similar to the crushing surrounding each tooth. Oops. Yeah, there it is…

Figure 2. the jugal of Dimorphodon adds depth to the tooth-bearing portion of the maxilla, adding to the impression of an antorbital fossa.

Figure 2. The jugal of Dimorphodon adds depth to the tooth-bearing portion of the maxilla, adding to the impression of an antorbital fossa, a fact overlooked by Nesbitt and Hone (2010).

Dimorphodon has one of the largest and lightest skulls of any early Jurassic or Triassic pterosaur. The nasal, antorbital and orbital fenestra made up the vast majority of the skull separated by the thinnest struts of bone in the Pterosauria. Like any good engineer Dimorphodon supported its grid-like struts with small triangles of bone, like the one at the base of the slender ascending process of the maxilla. Paper thin, this triangular support at the base of the cylindrical ascending process was identified as an antorbital fossa by Nesbitt and Hone (2010). No other pterosaur depresses, or thins this area, which may be thinner due to crushing. Note the areas between the maxillary teeth, which exhibit similar crushing. Nesbitt and Hone (2010) also failed to note the presence of the laminated jugal (Fig. 2), which adds depth to the tooth-bearing portion of the maxilla.

Raeticodactylus skull. Nesbitt and Hone (2010) say the red areas represent the antorbital fossa.

Figure 2. Raeticodactylus skull. According to Nesbitt and Hone (2010) the red areas represent the antorbital fossa. Here these areas are interpreted as the transverse width of the  girder-like ascending process (stronger to support that rhino-like horn when it’s called into action), and otherwise typically buried in the matrix. At the top the transverse lacrimal is equally wide in the Z-axis. Note the ventral view of the skull (in blue, twisted during crushing) that confirms we’re seeing the ventral aspect of the maxilla/lacrimal portion of the antorbital fenestra. Also note this purported antorbital fossa is not the same as that seen in Dimorphodon (Fig. 1). No homology here.

Raeticodactylus was also promoted by Nesbitt and Hone (2010) as having an antorbital fossa, but there’s no basal triangular support for the maxillary ascending process here. So the two do not reflect homologous morphologies (which should have raised a red flag, except they were so hell-bent on providing “evidence” for an archosaur connection they ignored or overlooked this key fact). Instead what we’re seeing is the crushed transverse width of the girder-like ascending process of the maxilla and the ventral aspect of the lacrimal and skull roof. The skull had to be stronger than a typical pterosaur skull. After all it was doing something with that rhino-like horn and this reinforcement tells us it wasn’t just for display~!

Bottom line: No mandibular fenestra. No antorbital fossa. Pterosaurs are not archosaurs.

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
Buckland W 1829. Proceedings of the Geological Society London, 1: 127
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 2011.  The early evolution of archosaurs: relationships and the origin of major clades.  Bulletin of the American Museum of Natural History 352: 292 pp. online pdf
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.
Sangster S 2001. Anatomy, functional morphology and systematics of Dimorphodon. Strata 11: 87-88

wiki/Dimorphodon

A New Basal Flapping Fenestrasaur!! – Kyrgyzsaurus – (not a Drepanosaur)

A semi-recent paper by Alifanov and Kurochkin (2011) just came to my attention. The authors presented a tiny Triassic (Madygen Formation) reptile, Kyrgyzsaurus bukhanchenkoi (Figs. 1, 2),  based on a crushed anterior skeleton (sans forelimbs) and impressive skin impressions. Alifanov and Kurochkin (2011) considered it the most archaic representative of the the family Drepanosauridae (which they wrongly attributed to the Archosauromorpha).

Figure 3. The origin of pterosaurs now includes Kyrgyzsaurus, nesting between Cosesaurus and Sharovipteryx.

Figure 3. The origin of pterosaurs now includes Kyrgyzsaurus, nesting between Cosesaurus and Sharovipteryx.

Unfortunately,
Alifanov and Kurochkin (2011) did not test their find against a wider gamut of taxa. They did not include Jesairosaurus, or Huehuecuetzpalli which both nested at the base of the drepanosaurs in the large reptile tree. Short trees like theirs’ are problematic at the get-go because they include no suitable outgroup taxa that would make the point that Kyrgyzsaurus would indeed nest where it does. Nor did they attempt a reconstruction. Alifanov and Kurochkin (2011) also misidentified several bones (see below for list), which is easy to do due to the crushed and slightly scattered remains.

Kyrgyzsaurus is small reptile with a 1-inch long very open skull and an elongated neck with parallelogram-shaped centra. The scapula is elongated and robust, as in Longisquama. The coracoid is quadrant-shaped, as in other basal fenestrasaurs starting with Cosesaurus. The rostrum was so short that the naris began over the premaxilla, unlike other fenestrasaurs. The skull was shorter than the cervicals, as in Sharovipteryx.

Figure 2. Updated figure of Kyrgyzsaurus. Note the tiny forelimbs and large hyoid, as in Sharovipteryx.

Figure 2. Updated figure of Kyrgyzsaurus. Note the tiny forelimbs and large hyoid, as in Sharovipteryx.

Soft Tissues
Kyrgyzsaurus includes a large scaly dewlap as preserved in Cosesaurus and Longisquama. A different sort of soft tissue was dorsal to the vertebrae. It was fibrous, presaging pycnofibers found in pterosaurs. Unfortunately the matrix is broken close to the body, preventing knowledge of any possible plumes along the back.

Reconstruction
Moving the colored bones back to their in vivo positions results in a lateral view (Fig. 2) and palatal view that fits readily within all aspects of the Fenestrasauria and distinct from all other known fenestrasaurs. This was no drepanosaur, but it -was- an outgroup to all known drepanosaurs.

Phylogenetic Analysis
Kyrgyzsaurus nested in the large reptile tree between Cosesaurus and Sharovipteryx. Indeed it looks like a cross between both with that short rostrum an autapomorphy. This specimen confirms observations made in Cosesaurus and other fenestrasaurs and these suggest Kyrgyzsaurus was also a bipedal flapping taxon and possibly a glider, but not a flyer. All those extradermal membranes were secondary sexual traits. So was flapping. These were the birds-of-paradise of the Triassic.

Size
The size is similar to other fenestrasaurs indicating that all known specimens are adults.

Flapping
Even though the forelimbs are missing, the elongated scapula and stemmed coracoid are identical to those found in Langobardisaurus and Cosesaurus through pterosaurs. Earlier we discussed how these were different than those of quadrupedal tritosaur lizards and that birds, bats and pterosaurs all have a similar morphology for flapping.

Location
The Madygen Formation also yielded Sharovipteryx and Longisquama, so this is confirmed as the birthplace of the pterosaurs. If we keep looking here we will find a larger variety of fenestrasaurs. Alifanov and Kurochkin (2011) listed several papers describing Longisquama and Sharovipteryx, but failed to mention any of my papers, so once again these paleontologists turned a blind eye to the most parsimonious hypotheses out there. That’s a shame. Ultimately, as in this blog, their mistakes and oversights will be revealed.

Mistakes
Alifanov and Kurochkin (2011) misidentified the dorsal scapula as a single high neural spine. They thought the lower jaw was shorter than the upper at their tips. The occiput was overlooked as it sits on top of the parietal. What they considered the occiput are the first two cervical vertebrae. What they considered the occipital condyle is the posterior cervical vertebrae 2 extending below cervical 3, as in all the other cervical vertebrae and as in pterosaurs and other fenestrasaurs. What they considered broken maxilla is the sclerotic ring. What they considered the sclerotic ring is the squamosal and the postorbital. What they considered the arch of the hypoglossal apparatus is the main portion of the quadrate together with the much thinner hyoid. Their quadrate is the pterygoid process of the quadrate. Their maxilla is actually the ectopalatine (ectopterygoid + palatine). It might have tiny teeth. Their nasal is the ascending process of the premaxilla. The more slender thoracic spine is the ventral stem of a displaced coracoid. The lacrimals and prefrontals were overlooked entirely.

Making a reconstruction is key to double-checking the identities of crushed bones as in this specimen. You know the whole thing is there. You know what bones to look for. Putting them back together confirms identities.

Drepanosaurid?
Alifanov and Kurochkin (2011) reported, “The new species is referred to drepanosaurids based on the large nares and orbits, low position of the quadrates, the absence of gradual transition between vertebrae of the cervical and thoracic regions, arched clavicles, subtriangular section of thoracic ribs, and cranial inclination of the dorsal end of the scapulae.” In the new reconstruction, the naris is not so large, the quadrates are just as low, the transition between the cervicals and thoracic vertebrae is gradual, clavicles are not arched, but fused to the sternal complex, the thoracic ribs are indeed subtriangular in section (not sure how this relates to drepanosaurids) and the scapulae are not cranially inclined. Their big mistake was not correctly identifying the displaced scapula and coracoid, considering both to be vertebral spines. Drepanosaurs nest close to fenestrasaurs in the large reptile tree.

And the rest of Kyrgyzsaurus?
Phylogenetic bracketing permits us to imagine a long-torso fenestrasaur with long hind limbs and an attenuated tail. The pelvis could be deep or shallow, but the ilial processes would be elongated. A prepubis and pteroid would be present. Whether the forelimbs were shorter or longer depends on whether Kyrgyzsaurus was closer to the lineage of Sharovipteryx or Longisquama. Considering the size of the scapula, I would guess the latter was more probable.

Yes
I dream of finding more fenestrasaurs like this. Thank you, very much, Wm. Parker for sending the pdf!

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

References
Alifanov VR and Kurochkin EN 2011. Kyrgyzsaurus bukhanchenkoi gen. et sp. nov., a new reptile from the triassic of southwestern KyrgyzstanPaleontological Journal 45(6): 639–647. doi:10.1134/S0031030111060025.

wiki/Kyrgyzsaurus

The Antorbital Fenestra of Drepanosaurs

The drepanosaurs are a rag-tag clade of slow-moving arboreal tritosaur lizards derived from Jesairosaurus in the large reptile tree. Drepanosaurs include Hypuronector, Vallesaurus, Megalancosaurus and Drepanosaurus in order of greater derivation.

The skull of Vallesaurus in situ.

Figure 1. The skull of Vallesaurus in situ. Difficult to interpret, to be sure, but I don’t see any large maxillary plates here. Perhaps palatal elements, though.

There has been some debate as to whether or not drepanosaurs had an antorbital fenestra. If so, this would have been the fifth (or perhaps the fourth since this clade is very close to Langobardisaurus and Cosesaurus) origin of the antorbital fenestra. Unfortunately only two drepanosaurs include skulls, Vallesaurus and Megalancosaurus. Here we’ll trace and reconstruct both. It’s no easy task.

The skull of Vallesaurus as interpreted by Renesto

Figure 2. The skull of Vallesaurus as interpreted by Renesto (2006). He found no evidence of an antorbital fenestra. The stem-like nasal and lacrimal are both present here. The question is, what, if anything, filled the space between them? Was it folded and flattened palatal bones? Renesto did not note any palatal elements here, yet they must have been present.

The palatal elements of Jesairosaurus,

Figure 3. The palatal elements of Jesairosaurus, the outgroup for the drepanosaurs. Fairly solid-looking. This contrasts with the lighter airier palates of fenestrasaurs and Megalancosaurus.

The palate
When skulls are crushed in lateral view, something has to happen to the transverse palatal elements. Typically they flip up or down, like playing cards, presenting their broadest surface to the matrix plane. It is difficult to discern the shape of the palatal elements in Vallesaurus, but if they were more solid, like the elements in Jesairosaurus, then this may account for the bone that Renesto found behind and through the rostrum (= antorbital fenestra).

In the more derived drepanosaur, Megalancosaurus (fig. 8) these solid elements were reduced to more gracile elements.

Figure 4. Interpretation of the skull elements of Vallesaurus. Note the slender ascending process of the maxilla in green.

Figure 4. Interpretation of the skull (sans palatal) elements of Vallesaurus. Note the slender ascending process of the maxilla in green and the slender lacrimal stem in magenta.

Interpretation of the skull of Vallesaurus based on figure 4.

Figure 5. Interpretation of the skull of Vallesaurus based on figure 4.

Vallesaurus
Talk about difficult skulls to trace (Figs. 1, 4), reconstruct and restore (Fig. 5)!! And remember, if we are looking at a light and airy skull, we’re looking through a light and airy skull to the right side elements obscured by intervening palatal elements. I did not attempt to outline the palatal elements in Vallesaurus, but considering the size of the eyes, the palate had to be nearly as wide as the height of the skull, as in Megalancosaurus.

Both part and counterpart of Megalancosaurus superimposed.

Figure 6. Both part and counterpart of Megalancosaurus superimposed using Photoshop.

Interpretation of figure 6, the skull of Megalancosaurus.

Figure 7. Interpretation of figure 6, the skull of Megalancosaurus. Struts of bone surround antorbital fenestra here. The slender ascending process of the left maxilla is convincing evidence for an antorbital fenestra in Megalancosaurus. The huge size of the naris is further evidence for skull lightening as a selective influence.

Megalancosaurus
The skull of Megalancosaurus was split in two, the part and counterpart (Figs. 6, 7). Reassembling them with software helps to realign the two crushed halves together for interpretation of the elements. What I see there is a slender ascending process of the maxilla. That can only occur if there is an antorbital fenestra. If that bone is another bone, then this will have to be reconsidered. At this point an antorbital fenestra seems likely. And I’m open to new data if anyone out there has some.

Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

Figure 8. Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

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
Calzavara M, Muscio G and Wild R 1980. Megalancosaurus preonensis n. gen. n. sp., a new reptile from the Norian of Friuli. Gortania 2: 59-64.
Feduccia A and Wild R 1993. Birdlike characters in the Triassic archosaur Megalancosaurus. Natur Wissenschaften 80:564–566.
Geist NR and Feduccia A 2000. Gravity-defying Behaviors: Identifying Models for Protoaves. American Zoologist 4):664-675. online pdf
Renesto S 1994. Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of Northern Italy. Journal of Vertebrate Paleontology 14(1):38-52.
Renesto S 2000. Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of Northern Italy. Rivista Italiana di Paleontologia e Stratigrafia 106: 157–179.
Renesto S and Binelli G 2006. ’Vallesaurus Cenensis“’ Wild, 1991, A Drepanosurid (Reptilia, Diapsida): From the Late Triassic of Northern Italy”, Rivista Italiana di Paleontologia e Stratigrafia 112: 77–94, Milano.
Wild R 1990. Ein Flugsaurierrest (Reptilia, Pterosauria) aus der Unterkreide (Hauterive) von Hannover (Niedersachsen). Neues Jahrbuch für Geologie und Paläontologie. Abhandlung 181,241–254.

wiki/Vallesaurus
wiki/Megalancosaurus

The Monofenestrata?

When Darwinopterus was first described (Lü et al. 2010) it was promoted as the transitional taxon uniting basal long-tailed pterosaurs with derived “pterodactyloid” pterosaurs, those with a united naris and antorbital fenestra. The Monofenestrata was a clade invented to include Darwinopterus and its kin along with traditional “pterodactyloids.” It has come to be accepted among pterosaur workers.

Unfortunately the original phylogenetic analysis (Lü et al. 2010) was poorly resolved, especially so at the transition point.

A larger pterosaur tree, including many more taxa, resolved the issue and found that Darwinopterus and kin nested with Pterorhynchus and this clade became extinct afterwards, leading to no other so-called “pterodactyloids.” In fact there were four convergent origins to the various “pterodactyloid” clades, not just one, as demonstrated by the large pterosaur study. These were derived from Dorygnathus and Scaphognathus (itself derived from Dorygnathus, too).

So, by this definition, the Monofenestrata is polyphyletic (not monophyletic) and therefore it has no value.

The enlargement of the skull in the Darwinopterus/Pterorhynchus clade along with the reduction and disappearance of the naris was convergent with the other four “pterodactyloid”-grade clades. Hence the confusion built on hope, perhaps for fame or resolution, not a comprehensive fully-resolved phylogenetic analysis.

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
Lü J, Unwin DM, Jin X, Liu Y and Ji Q 2009. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society London B  (DOI 10.1098/rspb.2009.1603.)
Lü J, Unwin DM, Deeming DC, Jin X, Liu Y and Ji Q 2011a. An egg-adult association, gender, and reproduction in pterosaurs. Science, 331(6015): 321-324. doi:10.1126/science.1197323
Lü J, Xu L, Chang H and Zhang X 2011b. A new darwinopterid pterosaur from the Middle Jurassic of Western Liaoning, northeastern China and its ecological implicaitions. Acta Geologica Sinica 85: 507-514.

wiki/Monofenestrata

Cerritosaurus – A Key Overlooked Taxon in the Pararchosauriformes

Cerritosaurus binsfeldi,

Figure 1. Cerritosaurus binsfeldi, Late Triassic, known only from a skull. Such a taxon was basal to Chanaresuchus and the chanaresuchids. It also would have been morphologically close to the ancestor of the phytosaurs (parasuchians) and not far from Proterochampsa given its resemblance to the RC 91 specimen of Youngoides.

Where are the Phytosaur and Chanaresuchid Ancestors?
There has been relatively little interest in finding ancestral taxa to the phytosaurs and chanaresuchids. Prior efforts have recovered questionable candidates. Nesbitt’s (2011) tome on archosaurs recovered Euparkeria nesting at the base of the Phytosauria.  He also recovered Vancleavea nesting at the base of the Proterochampsia (= Tropidosuchus + Chanaresuchus). Erythrosuchus nested basal to all the above taxa.

These Nestings Raise Red Flags
Phytosaurs and chanaresuchids were flat-headed archosauriformes with skulls wider than tall and nares located dorsally on the skull. The orbits were located high on the skull. The rostrum was narrow in dorsal view and the “cheeks” flared widely. The antorbital fenestra was small. By contrast the skulls of VancleaveaEuparkeria and Erythrosuchus were taller than wide, with narrow cheeks, lateral nares and the latter two had a large antorbital fenestra. Vancleavea did not have an antorbital, mandibular or upper temporal fenestra because indeed it was not related to archosaurs. Vancleavea was a thalattosaur as reported earlier. Nesbitt (2011) did not include other thalattosaurs in his analysis, so Vancleavea nested by default within the Archosauriformes. The large reptile study solves that shortcoming.

Cerritosaurus binsfeldi (Price 1946, Fig. 1) Late Triassic, ~210 mya, nests here between the Parasuchia and the base of the Chanaresuchidae within the Pararchosauriformes. Nesbitt (2011) briefly mentioned Cerritosaurus as a member of the Proterochampsia [a paraphyletic taxon]. With its short snout and generally primitive characters Cerritosaurus likely also resembled the common ancestor of the Choristodera, Parasuchia and Proterochampsa. It was also not far from the RC 91 specimen of Youngoides (Fig. 1).

Distinct from RC91Cerritosaurus had a skull with a downturned rostrum. The skull was box-like with distinct rims both anterior and posterior to the orbits. The nares opened dorsally. An antorbital fenestra appeared with a deep fossa. The dorsal squamosal flared posteriorly. The mandibular fenestra was enlarged. The retroarticular process ascended. The teeth were extremely long, which is an autapomorphy.

With its wide flat skull, dorsal nares and elevated orbits Cerritosaurus provides a nearly ideal transitional taxon linking the RC91 specimen of Youngoides to basal phytosaurs and chanaresuchids. It is certainly a superior candidate compared to the taller narrow skulls of Euparkeria and Erythrosuchus. Exclusion of Cerritosaurus by Nesbitt (2011) and others before him impaired those earlier studies.

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 1971Cerritosaurus binsfeldi Price, tipo de uma nova família de tecodontes (Pseudosuchia-Proterochampsia). Anais da Academia Brasileira de Ciências, 43(Supl.): 417-422.
Kischlat E-E and Schultz CL 1999. Phylogenetic analysis of Proterochampsia (Thecodontia: Archosauriformes): Ameghiniana, v. 36, p. 13R.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Price LI 1946. Sôbre um novo pseudosuquio do Triássico superior do Rio Grande do Sul: Boletim da Divisão de Geologia e Paleontologia, DNPM, v. 120, p. 7-38.

wiki/Cerritosaurus

Hexinlusaurus – A Small Heterodontosaur

This is a revision of an earlier blog on the same taxon.

A Basal Ornithischian of Uncertain Affinities
Hexinlusaurus multidens ZDM T6001 (He and Cai 1983, Barrett, Butler and Knoll 2005) middle Jurassic, was originally considered a basal ornithischian of uncertain affinities. Unfortunately the predentary area (anterior mandible) was not preserved, but the pelvis was standard for ornithischians with a completely retroverted pubis. A palpebral bone (“eyebrow” bone) was also present, as in other ornithischians.

Nesting in the Large Reptile Study
This blog originally found Hexinlusaurus to be  nested between the Sauropodomorpha and the Ornithischia, apparently linking these two clades of the Phytodinosauria. However, I noted then that with that pelvis morphology, Hexinlusaurus was 100% ornithischian.

Here, with further study, Hexinlusaurus nests with Heterodontosaurus (Fig. 1). The missing anterior likely included some fangs. The Middle Jurassic age of Hexinlusaurus compares to the Early Jurassic age of Heterodontosaurus.

Hexinlusaurus compared to its closest relative, Heterodontosaurus.

Hexinlusaurus compared to its closest relative, Heterodontosaurus. Is the size related to ontogeny or phylogeny? I don’t know.

A Single Autapomorphy
Barrett, Butler and Knoll (2005) described Hexinlusaurus with a single autapomorphy, a laterally concave postorbital. It appears that Heterodontosaurus has a similar postorbital depression.

Generally I Avoid the Dinosauria
There are very few dinosaurs in the present study, only basal taxa. The family tree of the Dinosauria is relatively uncontroversial and is better covered in detail elsewhere (and references therein).

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
Barrett PM, Butler RJ and Knoll F 2005. Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China. Journal of Vertebrate Paleontology 25:823-834.
He X-L and Cai K-J 1983.
A new species of Yandusaurus (hypsilophodont dinosaur) from the Middle Jurassic of Dashanpu, Zigong, Sichuan. Journal of Chengdu College of Geology, Supplement 1:5-14.

wiki/Hexinlusaurus

Pampadromaeus, Bridging the Theropod – Phytodinosaur Transition

Pampadromaeus barberenai 
Pampadromaeus barberenai
 (Cabriera et al. 2011) is a new dinosaur from the Late Triassic of Brazil. It was originally described as a stem sauropodomorph known from a partial disarticulated skeleton and most of the skull bones. The authors reported, “Based on four phylogenetic analyses, the new dinosaur fits consistently on the sauropodomorph stem, but lacks several typical features of sauropodomorphs, showing dinosaur plesiomorphies together with some neotheropod traits.”

Pampadromaeus in left lateral view.

Figure 1. Pampadromaeus in left lateral view. The skeleton was disarticulated and semi-complete.

Pampadromaeus was small (slightly longer than a meter in length) biped with a generalized basal dinosaur morphology, not quite a theropod and not quite a phytodinosaur (sauropods + ornithisuchians + pseudornithisichians).

The skull of Pampadromaeus

Figure 2. The skull of Pampadromaeus as it was originally reconstructed. Upper left: The skull of Eoraptor for comparison. To the left, images of the premaxilla and maxilla restored. Note the length of the premaxillary teeth and their proximal exposure. The newly mated premaxilla does not descend so much as in the original reconstruction.

Generalized Morphologies Generally Make for Great Transitional Taxa
Cabriera et al. (2011) added Pampadromaeus to four prior studies and in each case Pampadromaeus nested as a sister to Sauropodomorpha or as a sister to Saturnalia + Sauropodomorpha. Only ten taxa were included in each test. In each study Silesaurus + Ornithischia were outgroup taxa.

I added just the skull elements to the large reptile study (Fig. 3) and found it nested between members of the Theropoda and the Phytodinosauria, basal to its basalmost member, Daemonosaurus. Daemonosaurus was not included in the Cabriera et al. (2011) study based on prior studies. This nesting agrees with the Cabriera et al. (2011) results, but the expansion of the taxon list (Fig. 3) sheds more light on the nesting of this new and phylogenetically important dinosaur.

 the nesting site of Pampadromaeus

Figure 3. A portion of the large reptile tree indicating the nesting site of Pampadromaeus. Click to see the entire tree.

This is an Important Genus
Pampadromaeus is a key taxon linking theropods to all other dinosaurs, the herbivorous Phytodinosauria via Daemonosaurus. The enlargement of the premaxillary teeth observed in Daemonosaurus has its genesis in Pampadromaeus. The torso was shorter than in Saturnalia. The ilium resembled that of Herrerasaurus and Sanjuansaurus. The dorsal spines were lower than in Herrerasaurus. More detailed comparison can be found in Cabriera et al. (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
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