Raeticodactylus skull

Raeticodactylus (Fröbisch and Fröbisch 2006, Stecher 2008, Fig.1) is a skinny, nose–crested, Triassic pterosaur that nests with the holotype of Austriadactylus (Fig. 3), also a Triassic nose-crested pterosaur.

Figure 1. Raeticodactylus skull. Above, in situ and as originally interpreted. Middle: DGS tracing in color. Below: Reconstruction in lateral and palatal views. The missing part of the jugal may have lodged over quadrate, as it appears. The postorbital is broken into several pieces. The nasal extends a laminated layer over the premaxilla. The posterior pterygoid process is broken in situ and repaired here. One vomer is aligned with the premaxilla/maxilla suture. An ectopalatine (ectopterygoid + palatine) is displaced beneath the lacrimal. The mandible bones do not match the original drawing, but are closer to Eudimorphodon and other sister taxa. In all pterosaurs, the dentary approaches the coronoid process.

Figure 1. Raeticodactylus skull. Above, in situ and as originally interpreted. Middle: DGS tracing in color. Below: Reconstruction in lateral and palatal views. The missing part of the jugal may have lodged over quadrate, as it appears. The postorbital is broken into several pieces. The nasal extends a laminated layer over the premaxilla. The posterior pterygoid process is broken in situ and repaired here. One vomer is aligned with the premaxilla/maxilla suture. An ectopalatine (ectopterygoid + palatine) is displaced beneath the lacrimal. The mandible bones do not match the original drawing, but are closer to Eudimorphodon and other sister taxa. In all pterosaurs, the dentary approaches the coronoid process. Missing prefrontal and postfrontal indicated by black outline.

DGS and reinterpretation
The missing part of the jugal appears to have lodged over the quadrate. The coronoid, now on top of the jugal, has left a hole in the mandible posterior to the dentary. The postorbital is broken into several pieces and the central part is flipped (if correctly identified). The nasal extends a comb-like laminated layer over the premaxilla. The posterior pterygoid process is broken in situ and repaired here. One displaced vomer is aligned with the surface of the premaxilla/maxilla suture. An ectopalatine (ectopterygoid + palatine) is displaced beneath the lacrimal. The lacrimal is shorter than originally drawn. The mandible bones do not match the original drawing, but are closer to Eudimorphodon and other sister taxa. In all pterosaurs, the dentary approaches the coronoid process. The third anterior dentary tooth appears to have several roots, perhaps the result of tooth fusion. The prefrontal and postfrontal were not found.

All of these interpretations are tentative, but the reconstruction demonstrates these identifications fit established patterns. Take a look at the in situ postorbital. Only a colorized bone brings the pieces together visually. Dark outlines do not give such a visual cue.

Caviramus
An isolated mandible has been assigned to the genus Caviramus (Fig. 2). As in Raeticodactylus the articular extends posteriorly in an atypical fashion.

Figure 2. Caviramus (above) compared to Raeticodactylus (below) to the same length (on left) and to scale (on right). Caviramus mandible in lateral view showing the bony medial supports for the anterior teeth. The apparent mandible fenestra in Caviramus perhaps represents a missing coronoid.

Figure 2. Caviramus (above) compared to Raeticodactylus (below) to the same length (on left) and to scale (on right). Caviramus mandible in lateral view showing the bony medial supports for the anterior teeth. The apparent mandible fenestra in Caviramus perhaps represents a missing coronoid.

Nesbitt and Hone (2010) attempted to identify an antorbital fossa in Raeticodactylus, but this observation actually reflects the lateral thickness of the bone, reinforced to support the robust crushing teeth.

Figure 3. Austriadactylus (holotype) skull. Currently, with so few Triassic pterosaurs know, this is a sister to Raeticodactylus.

Figure 3. Austriadactylus (holotype) skull. Currently, with so few Triassic pterosaurs know, this is a sister to Raeticodactylus.

While we’re on the subject of Triassic pterosaur skulls,
let’s keep in mind Bergamodactylus (MPUM 6009, Fig. 4) and a sister to its predecessor, Longisquama, shown here to scale. Let’s remind ourselves that these fenestrasaur, tritosaur, lepidosaurs were very visual, especially when it came to secondary sexual characteristics. Crests, plumes and wings were all part of those differentiating packages once a pair of wings became standard equipment used for flying rather than solely for display.

http://www.reptileevolution.com/longisquama.htm

Figure 4. The skull of Bergamodactylus (MPUM 6009) together with that of Longisquama. Raeticodactylus had a more robust rostrum and mandibles, but was otherwise similar.

References
Fröbisch NB and Fröbisch J 2006. A new basal pterosaur genus from the upper Triassic of the Northern Calcareous Alps of Switzerland. Palaeontology 49 (5): 1081–1090. doi:10.1111/j.1475-4983.2006.00581.x. Retrieved 2007-03-02.
Nesbitt SJ and Hone DWE 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233
Stecher R 2008. A new Triassic pterosaur from Switzerland (Central Austroalpine, Grisons), Raeticodactylus filisurensis gen. et sp. nov.. Swiss Journal of Geosciences 101: 185. doi:10.1007/s00015-008-1252-6. Online First

wiki/Raeticodactylus

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Novel insights – part 2

Earlier we looked at some of the novel paleontological insights brought to you by reptileevolution.com. Today we’ll continue with the higher (new) lepidosauromorphs.

New Lepidosauromorpha 2

  1. Macroleter and Lanthanosuchus are sister taxa.
  2. Nyctiphruretus, Sauropareion and owenettids are not procolophonids. They are pre-lepidosauriformes.
  3. Coletta is not a procolophonid, but a basal lepidosauriform.
  4. Saurosternon and Palaegama are basal to the erroneously-called ‘rib’ gliders.
  5. Coelurosauravus and Mecistotrachelos are sisters to the kuehneosaurids with homologous dermal structures (not ribs).
  6. Xianglong is a late surviving sister to the kuehneosaurids, not related to Dracothe living rib glider, which does indeed glide with its ribs, distinct from the others.
  7. Basal lepidosaurs split between sphenodontids and tritosaurs + pre-squamates.
  8. Basal sphenodontids include Megachirella, Pleurosaurus and Marmoretta.
  9. Derived sphenodontids include Azendohsaurus, Trilophosaurus, rhynchosaurs and their kin with several taxa, like Eohyosaurus as transitional taxa.
  10. Tritosauria is an overlooked clade of lepidosaurs. It contains Huehuecuetzpalli, Tijubina, MacrocnemusLangobardisaurus, Tanystropheus and the fenestrasaurs, Cosesaurus, Sharovipteryx, Longisquama and pterosaurs.
  11. Lacertulus, Hoyalacerta and others are proto-squamates, nesting outside of the Squamata.
  12. Scandensia, Calanguban and Euposaurus are basal squamates.
  13. Geckos are the sister group to the clade that produced snakes.
  14. Ardeosaurus is a basal member of that proto-snake/snake clade that has aquatic members, like Pontosaurus, not related to mosasaurs.
  15. Burrowing snakes, like Leptotyphlops, are derived, not basal snakes.
  16. Amphisbaenids and Dibamus are derived skinks.
  17. Jesairosaurus and the drepanosaurs nest with kuehneosaurs as basal lepidosauriforms.

More later. Celebrating four years online this month.

Eudibamus skull revisited

Unfortunately,
requests for hi-rez images of the skull of Eudibamus (Berman et al. 2000) have gone unanswered.

Fortunately,
an image from a Stuart Sumida lab pdf file (Fig. 1) provides the best image I’ve seen so far. Even so, it could be better.

Figure 1. GIF movie of the skull of Eudibamus along with a DGS interpretation of the elements. A reconstruction (Fig. 2) appears to 'make sense" but I'd still like to see better resolution.

Figure 1. GIF movie of the skull of Eudibamus along with the original (line art) interpretation and a DGS interpretation of the elements. Where are the teeth in the line art? They are not indicated. A reconstruction based on the DGS tracings (Fig. 2) appears to ‘make sense” but I’d still like to see better resolution. The presumed mandible here does not have the appearance of the rest of the bones. The mandible is based on a possible impression that looks like it has teeth. These could be pick marks. Black lines in the color tracing appear to represent palatal elements that basically match those of Petrolacosaurus.

Eudibamus is still considered a bolosaurid
(Fig. 2) in traditional paleontology, but it nests with basal diapsids, like Petrolacosaurus, in the large reptile tree. We looked at Eudibamus earlier here, here and here.

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

This skull remains confusing.
This is only an attempt at understanding it. Higher resolution and color would be helpful. The original authors did not publish a skull reconstruction, nor did they label individual skull bones. I wonder if they were just as confused, even with the skull in front of them.

 Eudibamus reconstruted.

Figure 3. Eudibamus reconstructed. This will probably not be the last such attempt. But I think it is the most accurate so far.

References
Berman, DS, Reisz RR, Scott D, Henrici AC, Sumida SS and Martens T 2000. Early Permian bipedal reptile. Science 290: 969-972.

Tetrapodophis – new four legged very basal, very tiny snake – part 2

Earlier we looked at the skull of Tetrapodophis (Martill et al. 2015), a four-legged very tiny snake.

Figure 1. Tetrapodophis nests at the base of the clade of snakes in the large reptile tree.

Figure 1. Tetrapodophis nests at the base of the clade of snakes in the large reptile tree. Note, the burrowing snakes are not basal in this tree. Rather these very specialized snakes are quite derived. There are more proto-snakes and basal snakes known, so this tree should be considered in that light.

A phylogenetic analysis nested Tetrapodophis at the base of all snakes (Fig. 1).

Figure 2. The skulls of pre-snakes, Tetrapodophis and snakes compared. The orbits move foreword. The jaw muscles enlarge. The upper temporal arch disappears.

Figure 2. The skulls of pre-snakes, Tetrapodophis and snakes compared. The orbits move foreword. The jaw muscles enlarge. The upper temporal arch disappears.

National Geographic featured several Dave Martill quotes. Here are a few:

“And then, if my jaw hadn’t already dropped enough, it dropped right to the floor,” says Martill. The little creature had a pair of hind legs. “I thought: bloody hell! And I looked closer and the little label said: Unknown fossil. Understatement!”

“I looked even closer—and my jaw was already on the floor by now—and I saw that it had tiny little front legs!” he says.

“But no snake has ever been found with four legs. This is a once-in-a-lifetime discovery.”

“This little animal is the Archaeopteryx of the squamate world,” he says.

Martill thinks that Tetrapodophis killed its prey by constriction, like many modern snakes do. “Why else have a really long body?” he says.

Martill thinks that the snake may have used these “strange, spoon-shaped feet” to restrain struggling prey—or maybe mates.

There was a bit of controversy raised about this specimen. Read about it here at Forbes.com. It also includes an illustration of Tetrapodophis wrapped around a mouse-like mammal. Tiny prey bones were found in its gut.

Likely a Crato Formation fossil
Martill et al. thought the Tetrapodophis substrate was from the Crato Formation. Wikipeidea reports, “The Crato Formation is a geologic formation of Early Cretaceous age in northeastern Brazil‘s Araripe Basin. It is an important Lagerstätte (undisturbed fossil accumulation) for palaeontologists. The strata were laid down mostly during the early Albian age, about 108 million years ago, in a shallow inland sea. At that time, the South Atlantic was opening up in a long narrow shallow sea.”

Nevertheless,
Martill et al. consider Tetrapodophis closer to burrowing snakes, not aquatic ones. Distinct from its sea-going predecessors, Tetrapodphis had a longer torso than tail, like living snakes do. It also had a single row of belly scales, like snakes, preserved as soft tissue impressions.

Perhaps,
owing to its small size, Tetrapodophis had returned to the land, or shallows grading to swamps.

Video link 1. Dave Martill describing from large photos Tetrapodophis. Just a few minutes long.

Video link 1. Dave Martill describing from large photos Tetrapodophis. Just a few minutes long.

Finally,
here’s Dave Martill in a video describing Tetrapodophis. Click to play.

References
Martill DM, Tischlinger H and Longrich NR 2015. A four-legged snake from the Early Cretaceous of Gondwana. Science 349 (6246): 416-419. DOI: 10.1126/science.aaa9208

Novel insights – part 1

Not much news lately,
so a bit of a review in the current storms of controversy and disparagement.

In the last four years
adding species- and specimen-based taxa to the large reptile tree and large pterosaur tree and creating reconstructions, at times using DGS, have provided a rich trove of novel insights into reptile evolution heretofore (and too often currently) unnoticed, overlooked and ignored. Of course, these all need to be tested in independent studies using similar taxon lists along with any novel list of character traits exceeding 150-200 in number.

Amniota

  1. Initial split of the Amniota into Lepidosauromorpha and Archosauromorpha clades. That means Amniota = Reptilia.
  2. Gephyrostegus bohemicus is a sister to the last common Viséan (or earlier) ancestor of all Amniotes. It lacks traditional amniote skeletal traits, but lacks posterior dorsal ribs, creating a larger volume for gravid females to hold larger eggs, a deeper pelvic opening and unfused pelvic elements.
  3. Proximal outgroup taxa to the Amniota include sisters to Silvanerpeton, Utegenia and members of the Seymouriamorpha in order of increasing distance.
  4. As in many prior studies, phylogenetic miniaturization is key to the origin of several clades.

Lepidosauromorpha

  1. Basal lepidosauromorphs include the clade of Urumqia, Brukterepeton and Thuringothyris. Some of these were formerly considered anamniotes.
  2. Captorhinomorph sister taxa include Cephalerpeton, Reiszhorhinus, Concordia and Romeria primus. Romeria texana is a basal captorhinomorph.
  3. A sister to Saurorictus is basal to all remaining lepidosauromorphs, Diadectormorpha + Millerettidae.
  4. Diadectomorphs are lepidosauromorph reptiles.
  5. Procolophon and kin are sisters to diadectomorphs like Oradectes, Silvadectes and Diadectes. A sister to Orobates is their last common ancestor.
  6. Colobomycter is a basal procolophonid.
  7. Tetraceratops is a sister to Tseajaia and Limnoscelis and these three are sisters to the Diadectes + Procolophon clade.
  8. Caseasauria are millerettids, not synapsids and caseasauria is a sister clade to Feeserpeton + Australothyris + Eunotosaurus + Acleistorhinus + Delorhynchus.
  9. Bolosaurids are also millerettids  and are basal to the Stephanospondylus clade.
  10. Stephanospondylus is basal to the pariasaur + turtle clade.
  11. Sclerosaurus is basal to the turtle clade.
  12. ElginiaMeolania nest as basalmost turtles along with Proganochelys.
  13. Odontochelys nests with Trionyx, a soft-shell turtle. Skull emargination and tooth loss was convergent in soft shell  and hard shell turtles.

More later.

Tetrapodophis – new four legged very basal, very tiny snake

A new paper by Martill, Tischlinger and Longrich (2015) brings us a really tiny, new Early Cretaceous snake, Tetrapodophis amplectus (Fig. 1, BMMS BK 2-2, ), with four limbs and all of its fingers and toes. The authors suggest this basal snake and thus all snakes evolved from burrowing rather than marine ancestors in accord with the  Longrich, Bullar and Gauthier (2012) assessment of another tiny snake, Coniophis, which is known from only a few skull parts. (Also see below.)

Unfortunately Tetradopodophis (so far based on skull traits only) nests in the large reptile tree between Adriosaurus + Pontosaurus and DinilysiaPachyrhachis + Boa, so an aquatic origin is recovered from the cladogram despite the extremely tiny size of Tetrapodophis (skull length about 1 cm, total length about 16 cm). Martill et al. used mosasaurs and several incomplete taxa (Eophis, Diablophis, Portugalophis and Parviraptor, none included in the large reptile tree) for outgroups and nested Tetrapodophis as a sister to Coniophis and basal to Najash, Dinilysia and all other snakes. The authors note, “As the only known four-legged snake, Tetrapodophis sheds light on the evolution of snakes from lizards. Tetrapodophis lacks aquatic adaptations (such as pachyostosis or a long, laterally compressed tail) and instead exhibits features of fossorial snakes and lizards: a short rostrum and elongation of the postorbital skull, a long trunk and short tail, short neural spines, and highly reduced limbs.”

I wonder if Tetrapodophis is a hatchling? Or does it represent yet another example of phylogenetic miniaturization at the origin of a major clade? It is similar in size to Jucaraseps, a more primitive lizard with snake affinities. Tetrapodophis may be a late surviving (Early Cretaceous) very basal snake with likely origins in the Middle Jurassic. DGS (digital graphic segregation) was helpful in pulling out details (Fig. 1) overlooked or ignored by the original authors.

Figure1. The skull of Tetrapodophis in situ and colorized (middle) as originally interpreted (below) and reconstructed using DGS (above). I have not seen the fossil, but examination of the photograph using DGS permits more details to be identified. This image will be tested for validity Monday. Only the major bones were identified here. The skull is about 1 cm in length.

Figure1. The skull of Tetrapodophis in situ and colorized (middle) as originally interpreted (below) and reconstructed using DGS (above). I have not seen the fossil, but examination of the photograph using DGS permits more details to be identified. This image will be tested for validity Monday. Only the major bones were identified here. The skull is about 1 cm in length.

The preparator did an excellent job on such a tiny (16 cm) specimen, unless it split naturally into part and counterpart. The specimen was in a private collection for decades before getting its museum number.

Like non-snakes, Tetrapodophis retained a postorbital, squamosal and lacrimal. A broken jugal was also found. Palatal fangs were present along with a deep coronoid process. There is a mass at the back of the throat that makes it difficult to identify the posterior palatal bones. The authors report, BMMS BK 2-2 is distinguished from all other snakes by the following combination of characters: 160 precaudal and 112 caudal vertebrae, short neural spines, four limbs, metapodials short, penultimate phalanges hyper elongate and curved, phalangeal formula 2?-3-3-3-3? (manus) 2-3-3-3-3 (pes).”

Although DGS was able to pull lots of details out of this specimen, don’t expect the DGS detractors to applaud this example, although It would be nice to get a tip of the hat for this one. It’s a pretty striking example and only took an hour or two to do.

Figure 2. Tiny Tetrapodophis at full scale if your monitor produces 72 dpi images (standard on many monitors).

Figure 2. Tiny Tetrapodophis at full scale if your monitor produces 72 dpi images (standard on many monitors).

This is a major find and congratulations are due to the authors. More on this specimen in future blog posts.

References Longrich NR, Bullar B-A S and Gauthier JA 2012. A transitional snake from the Late Cretaceous period of North America. Nature 488, 205-208. Martill DM, Tischlinger H and Longrich NR 2015. A four-legged snake from the Early Cretaceous of Gondwana. Science 349 (6246): 416-419. DOI: 10.1126/science.aaa9208

Invagination and erosion of the turtle cranium

Turtles have no temporal fenestra,
but some of them have enlarged their jaw muscles by greatly enlarging the cranium, or by invagination of the cranium from the occiput, or both (Fig. 1). Skull temporal fenestra are important traits to categorize most reptiles, but turtles do not follow other clade morphologies. That has made turtles difficult to categorize and nest in traditional studies.

Figure 1. Macrochelys (Macroclemys) skull colorized. Most workers label the bone above the curled quadrate as a squamosal, but here it is considered a supratemporal, which has horns in basal turtles.

Figure 1. Macrochelys (Macroclemys) skull colorized. Most workers label the bone above the curled quadrate as a squamosal, but here it is considered a supratemporal, which has horns in basal turtles. This skull shows a minimum of occiput invagination, but note the great height of the cranium.

Some paleontologists
think turtles are diapsids related to placodonts, but that is not supported by the large reptile tree.

Other paleontologists
think turtles are anapsids related to Eunotosaurus, but that is not supported by the large reptile tree.

Still other paleontologists
USED to think turtles are anapsids related to pareiasaurs, and that IS supported by the large reptile tree. Basal turtles, like pareiasaurs and all basal tetrapods, have both an external (dermal) skull  surrounding and protecting the smaller internal (braincase) skull.

Basal turtles have a solid cranium – with horns!
Elginia and Meiolania are basalmost turtles they have horns and at least we know that Meiolania had a solid carapace and plastron. The outgroup, Sclerosaurus, has horns, but no shell and no broad ribs. In Meiolania the large, horned supratemporal sends a ventral process to contact the quadratojugal leaving a hole for the quadrate and stapes (ear bone). The supratemporal is a large bone in basal turtles that does not go away in derived turtles. Rather, the squamosal continues to shrink.

Figure 2. Elginia and Meiolania, two basal horned turtles without skull invagination.

Figure 2. Elginia and Meiolania, two basal horned turtles without skull invagination. In Meiolania the supratemporal sends a ventral process to contact  the quadratojugal leaving a hole for the quadrate and stapes (ear bone). The supratemporal is a large bone in basal turtles that does not go away in derived turtles. Rather, the squamosal continues to shrink.

Proganochelys (Fig. 3) has long been recognized as a basal turtle. It has no horns or skull invagination, so, in this context, it is not a basal turtle, but a transitional turtle, between horned and invaginated-skull turtles.

Figure 2. The skull of Proganochelys, a basal turtle without skull invagation and without horns.

Figure 3. The skull of Proganochelys, a basal turtle without skull invagation and without horns. Note the identification of the supratemporal on the right matching that of basal turtles like Elginia and Meiloania in figure 2.

Softshell turtles
have an invaginated cranium, no horns and sometimes reduce their bony shells. A basal turtle with teeth, Odontochelys, nests with a soft-shell turtle, Trionyx, in the large reptile tree. The cranium of Trionyx is invaginated from the occiput, creating space for large jaw muscles. The skull of Odontochelys (Fig. 7) is difficult to study with available data, but it appears to have large round holes in the crushed cranium. At least it does not appear to have the solid cranium that was illustrated originally (Fig. 7). Rather the cranium appears to be so badly crushed, even in the low resolution image available, that it may indeed have had a more fragile, less box-like, Trionyx-like cranium. I requested high rez images, but was informed that another paper focusing on the skull of Odontochelys is in progress. Looking forward to that!

Figure 3. Trionyx, a softshell turtle with bones colorized.

Figure 3. Trionyx, a softshell turtle with bones colorized.

Other tested turtles have a an increasingly invaginated cranium
Chelonia,
the sea turtle, is a basal turtle that has a rather solid skull with a little posterior invagination.

Macrochelys, the alligator snapping turtle (Fig. 1), has a deeper invagination and a much taller cranium.

Pelomedusa and Foxemys are similar to the snapping turtle, but without the grand enlargement of the cranium.

Terrapene (Fig. 5), the box turtle, has lost most of its original cranium, revealing a braincase, like a mammal, snake, amphisbaenid or bird.

Figure 4. Terrapene, the box turtle, with skull bones colorized. Note the lack of a dermal skull and the appearance of the cranial skull, the braincase.

Figure 5. Terrapene, the box turtle, with skull bones colorized. Note the lack of a dermal skull and the appearance of the cranial skull, the braincase, as in birds, mammals, snakes and amphisbaenids.

The large reptile tree
nests Kayentachelys between the soft-shell turtles, Trionyx and the hard-shelled turtles, like Chelonia (Fig. 6). Kayentachelys has a complete cranium without invagination. Separate nestings of soft-shell and hard-shell turtles with skull invagination indicate this trait was convergent, not homologous. Such a tree topology has not been recovered before, but then no prior study (that I can recall) has included Sclerosaurus, Elginia and Stephanospondylus.

Figure 1. Turtle phylogeny showing extent of horns and cranial invagination. Here the skull invagination of soft-shell turtles is convergent with that of most other turtles.

Figure 6. Turtle phylogeny showing extent of horns and cranial invagination. Here the skull invagination of soft-shell turtles is convergent with that of most other turtles.

Parts of the skull of Odontochelys cannot be accurately reconstructed with available data (Fig. 7). There are apparent temporal fenestrae in the in situ specimen exposed in dorsal view. These would ordinarily have the appearance of diapsid openings and would lend credence to the diapsid hypothesis of turtle origins. Instead, let’s wonder if these holes represent either: 1) geological erosion; or 2) erosion of the posterior cranium in spots transitional to the morphology seen in Trionyx. There’s nothing else I can say at present until better data comes along.

There is a large circular plate
(Fig. 7) in the palatal view of the smaller Odontochelys that was labeled a possible squamosal. I don’t think there is room on the skull for that bone at present. So that elliptical bone may be from elsewhere, perhaps on the carapace or plastron.

Most turtles have anterior nares.
The anterolateral placement of the large naris in Odontchelys is different from all other turtles and similar only to Elginia (Fig. 2).

Figure 7. Data and tentative interpretations of skull elements for Odontochelys. I can't make more sense than this of the bones. Sorry. Gray areas appear to represent holes in the cranium.

Figure 7. Data and tentative interpretations of skull elements for Odontochelys. I can’t make more sense than this of the bones. Sorry. Gray areas appear to represent holes in the cranium. Note the difference between the original drawing and the photo with color overlay. The skull bones of Odontochelys appear to be more fragile than boxy turtle skulls are.

The skull of Stephanospondylus (Fig. 8) is a good starting point for both pareiasaur and turtle skulls. It nests (Fig. 7) at the base of both clades.

Figure 2. Stephanospondylus skull in two views. Note the rotation of the post parietals to the dorsal skull along with the transformation of the supratemporals into small horns.

Figure 8. Stephanospondylus skull in two views. Note the rotation of the post parietals to the dorsal skull along with the transformation of the supratemporals into small horns.

Perhaps more taxa
will someday unite soft-shell turtles with hard-shell turtles, but at present, the convergence is remarkable among all turtles with an invaginated skull. With regard to Odontochelys, I think we’ll see a strong revision of the original drawing.

References
Li C, Wu X-C, Rieppel O, Wang L-T and Zhao L-J 2008. An ancestral turtle from the Late Triassic of southwestern China. Nature 456: 497-501.