Restoring the skull of Quetzalcoatlus sp.

We know of at least three partial skulls of Quetzalcoatlus sp. (Kellner and Langston 1996), the smaller version of Q. northropi (Lawson 1975), for which no skull is known. This is how Kellner and Langston (1996) reconstructed the skull.

Figure 1. Quetzalcoatlus sp. skull according to Kellner and Langston (1996).

Since this is such a popular pterosaur, many have attempted restorations based on their access to the specimen and their own artistic license. See one here and another here.

Here’s how I do it.
Below are images traced from Kellner and Langston (1996), scaled to the same scale (they were nearly identical in length and proportion) then combined to create the restoration (Fig.1).

Figure 2. Quetzalcoatlus skulls individually and combined to create a restoration. Not preserved possible soft tissue in gray. Back of the skull based on chaoyangopterids and Zhejiangopterus. Not sure what to make of the two bony crest shapes (red and black), whether a result of taphonomy or individual variation. Considering the angle between the cranial and rostral parts of this skull, apparently Q kept its snout down, not out. 

The skull turns out to be a little taller due to a low rostral crest, with a taller antorbital fenestra. Kellner and Langson (1996) assumed that the dentary continued on to more of a point and that may be so considering the example of Azhdarcho. The details and sutures of the skull are sometimes easy to make out but otherwise the texture of the gnarled bone  makes things more difficult.

All the same size? Yes.
And what does that mean? Were all three specimens juveniles of the same age? Or adults of the same age but of a species distinct from Q. northropi? I don’t know.

Figure 3. The dentary tip of the TMM 42161 specimen, twisted and skewed in dorsal view. Not sure what to make of this. If the tip does extend further (in pink), it likely does not extend very much further. The tip currently has the shape of a yardstick with some added ridges and valleys. Color represent distinct areas, not distinct bone. This is the anterior part of paired fused bones, the dentaries. Bottom view skewed segments unskewed. This dentary tip is wider than tall, unlike the tip of Eopteranodon and Eoazzhdarcho. Green areas are hypothetical lines to join and continue apparent missing areas. 

The dentary tip
I can only wonder what is going on at the tip of this dentary. It was skewed left and right several times, but in lateral view it appears undistorted. Distinct from sharp-jawed and tooth-tipped Eopteranodon and Eoazhdarcho (which are not azhdarchids), this rostral tip Fig. 3) is wider than tall, like a yardstick. It doesn’t appear strong enough to battle prey that fights back, but supports a gentle wading after tiny crustacean lifestyle.

References
Kellner AWA and Langston W 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from late Cretaceous sediments of Big Bend National Park, Texas. – Journal of Vertebrate Paleontology 16: 222–231.
Lawson DA 1975. Pterosaur from the latest Cretaceous of West Texas: discovery of the largest flying creature. Science 187: 947-948.

wiki/Quetzalcoatlus

A tree topology change – turtles and pareiasaurs move from diadectids to millerettids

I spent last week adding taxa and running through potential problems with the large reptile tree. Several matrix boxes were rescored. The result shifted turtles + pareiasaurs from Diadectides + Procolophon  to Milleretta RC70 + Odontochelys (a near-turtle now, not a real turtle), which we discussed earlier.

An interesting shift. 
Moving pareiasaurs + Proganochelys back to Diadectes + Procolophon now adds 22 steps. Moving pareiasaurs + turtles to Eunotosaurus (following the results of Lyson et al. 2013) adds 28 steps.

The RC14 specimen of Milleretta is still in the same clade as Acleistorhinus + Eunotosaurus + Austraolthyris + Feeserpeton + Belebey + Bolosaurus. 

Maybe not as crazy as it sounds
It’s the “plain brown sparrows” like Milleretta, that lie at the bases of major clades, not the highly derived taxa, like Procolophon and Diadectes. Those become extinct. The various specimens of Milleretta have long been ignored, but they really are the keys to understanding the reptile family tree.

References
Broom R 1913. On the Structure and Affinities of Bolosaurus. Bulletin of the American Museum of Natural History 32:509-516
Broom R 1938 On the Structure of the Reptilian Tarsus: Proceedings of the Zoological Society of London, v. 133, 108, p. 535-542.
Broom R 1948. A contribution to our knowledge of the vertebrates of the Karroo beds of South Africa: Transactions of the Royal Society of Edinburgh, Endinburgh 61: 577-629.
Case EC 1907. Description of the Skull of Bolosaurus striatus Cope. Bulletin of the American Museum of Natural History 23:653-658
Cope ED 1878. Descriptions of extinct Batrachia and Reptilia from the Permian formations of Texas. Proceedings of the American Philosophical Society 17:505-530
Gow CE 1972. The osteology and relationships of the Millerettidae (Reptilia: Cotylosauria). Journal of Zoology, London 167:219-264.
Watson DMS 1954. On Bolosaurus and the origin and classification of reptiles.Bulletin of the Museum of Comparative Zoology at Harvard College,, v. 111, no. 9444-449.

wiki/Milleretta
wiki/Bolosaurus

Broomia – A sister for Milleropsis – not Milleretta

Figure 1. Broomia. A long-recognized sister to Milleropsis, an early possible biped. Check out those thighs!

Broomia perplexa (Watson 1914, Thommasen and Carroll 1981, Middle Permian) was considered a millerettid and a descendant of romerid - catorhinomorphs, considerably older than other millerettids. The large reptile tree nested Broomia away from the millerettids among the new Lepidosauromorpha, but right next to Milleropsis, among the new Archosauromorpha close to the origin of the Diapsida and Petrolacosaurus. A shame we can’t see the top of the skull! Those long legs, robust femora, strong tarsals and large feet give the impression that Broomia was a strong runner.

Millerettids perplexed Carroll in 1981 and again in 1988 in the days before phylogenetic analysis. Today, due to the large reptile tree, we know the original members are diphyletic (not related), but developed similar traits by convergence.

Broomia has a lateral temporal fenestra derived from basal synapsid ancestors like Aerosaurus and Heleosaurus. mimicking millerettids and caseids. Unlike lepidosaurs, Broomia lacked an ossified sternum or fenestrated pectoral girdles.

Thommasen and Carroll (1981) note the disappearance of the millerettids about the time that lizards first appeared in the Late Permian. Millerettids gave rise to turtles and lepidosaurs via owenettids and early lepidosauriformes. Milleropsids, like Broomia, gave rise to enaliosaurs and protorosaurs, which ultimately produced archosaurs.

References
Thommasen H and Carroll RL 1981. Broomia, the Oldest Known Millerettid Reptile. Paleontology 24(2): 379-390.
Carroll RL 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Company, New York 1-698.
Watson  DMS 1914. Broomia perplexa gen et sp. nov., a fossil reptile from South Africa. Proceedings of the Zoological Society of Londont 995-1010.

The origin of pareiasaurs (and turtles).

Figure1. Pareiasaur (Anthodon) and its phylogenetic predecessor, Stephanospondylus, a robust millerettid and an ancestor to turtles. Note the close correspondence of dorsal skull elements.

Earlier we looked at the ancestry of turtles (starting with Proganochelys and Stephanospondylus) and near-turtles (starting with Odontochelys and the RC70 specimen of Milleretta). According to the large reptile tree, the closest sister taxon to Stephanospondylus and turtles is the clade Pareiasauria, represented above by Anthodon (Fig. 1). Stephanospondylus thus represents the closest known sister to pareiasaurs followed more distantly by the RC70 specimen of Milleretta. So pareiasaurs AND turtles are really just robust millerettids, which raises millerettid status from “huh? and “obscure” to “waiting in the wings.”

Figure 2 Arganaceras, as originally reconstructed and modified.

Stephanospondylus doesn’t have much cheek flare because its closer to turtles. For that we look to the basal pareiasaur, Arganaceras. Stephanospondylus also begat Elginia and Sclerosaurus, the “horned toads” of the Middle Triassic.

Figure 3. Sclerosaurus, a sister to pareiasaurs that perhaps gives some insight into the postcrania of Stephanospondylus , Milleretta RC70 and the ancestry of turtles and Odontochelys.

Sues and Reisz (2008) considered Sclerosaurus a procolophonid, but their concept of a procolophonid was much greater than the results of the large reptile tree.

Figure 4. The skulls of (left to right) the RC70 specimen of Milleretta, Odontochelys, Stephanospondylus and Proganochelys. The two on the left belong to a distinct clade and the two on the right belong to a distinct clade along with pareiasaurs. Odontochelys is more closely related to this specimen of Milleretta than to Stephanospondylus and Proganochelys.

References
Broom R 1938 On the Structure of the Reptilian Tarsus: Proceedings of the Zoological Society of London, v. 133, 108, p. 535-542.
Broom R 1948. A contribution to our knowledge of the vertebrates of the Karroo beds of South Africa: Transactions of the Royal Society of Edinburgh, Endinburgh 61: 577-629.
Gow CE 1972. The osteology and relationships of the Millerettidae (Reptilia: Cotylosauria). Journal of Zoology, London 167:219-264.
Hartmann-Weinberg AP 1933. Evolution der Pareiasauriden: Trudy Palaeontological institute Academe Nauk, SSSR, 1933, n. 3, p. 1-66.
Lee MSY 1997. Pareiasaur phylogeny and the origin of turtles. Zoological Journal of the Linnean Society 120: 197-280.
Owen R 1876. Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the Collection of the British Museum. London, British Museum (Natural History).
Sues H-D and Reisz RR 2008. Anatomy and Phylogenetic Relationships of Sclerosaurus armatus (Amniota: Parareptilia) from the Buntsandstein (Triassic) of Europe. Journal of Vertebrate Paleontology 28(4):1031-1042. doi: 10.1671/0272-4634-28.4.1031 online

wiki/Anthodon
wiki/Deltavjatia
Deltavjatia paleocritti
wiki/Pareiasaur
Sclerosaurus paleocritti
wiki/Milleretta

Dorygnathus – where are the postorbital bones? DGS to the rescue.

My first encounter with the UUPM R156 (Uppsala Museum, Sweden) Dorygnathus was in Wellnhofer (1991), the famous pterosaur encyclopedia. The image was small and produced with halftone dots. Nevertheless I produced a reconstruction from it and I used the fuzzy data in the large pterosaur tree.

The resolution question.
There are a whole raft of pterosaur workers who dismiss such efforts gleaned from photographs, both of poor quality and excellent. Some photographic data comes from publications. Other data comes from photographs I’ve taken on various trips to visit the specimens. Sometimes those photos come in handy long after the trip is over as new insights come in randomly.

Now let’s draw a parallel. There was a time, before the advent of the Hubble telescope and the Voyager and other flyby satellites, when the best images we could get of the planets came form Earth-bound telescopes beneath an ocean of atmosphere. Fuzzy is the best way to describe them. The broiling atmosphere was the problem. Even in photos from the largest telescopes there’s not a a lot of resolution. Then, after 1990, Hubble images provided a magnitude leap in resolution because they were taken far above the atmosphere.

Figure 1. The planet Jupiter as seen from above the atmosphere (Hubble) and below (Hale). Having a poor resolution photo did not impede astronomers from gathering data on Jupiter.

But did that stop astronomers from studying Jupiter?  No. You take what you’re given. And when you’re given better data you refine your hypotheses. What you don’t do is denigrate others for gathering data using the best available data, fuzzy though it may be. That is what the opposing camp of traditional pterosaur experts (Naish, Witton, Bennett, Hone, Unwin) do. Those are the experts you’ll recall, who are most responsible for disfiguring pterosaurs. They are still hoping that pterosaurs had deep chord wing membranes, fingers that faced palms forward in flight, babies that did not look like grownups, strong sexual dimorphism, eggs that were buried under rotting vegetation, a cruropatagium controlled by the lateral digits and, perhaps worst of all, they still have no idea what pterosaurs are despite being given the answer some 12 years ago (Peters 2000). They could have discovered what pterosaurs are, just by testing, looking and comparing. But they refuse to. 

Getting back to Dorygnathus R156
The skull of the R156 specimen (Fig. 2) appeared online and it offered better resolution than the Wellnhofer (1991) print. So I applied DGS to it and discovered several previously “missing” bones. None of these have been documented yet, as far as I know. Padian (2009) did not illustrate this specimen in his recent treatise on Dorygnathus, but described it nevertheless. Padian (2009) reported that Wiman (1925) wrote a detailed paper on the specimen.

Figure 2. Click to enlarge. Here is the R156 specimen of Dorygnathus. It looks like a complete skull, but can you find the postorbital. pterygoid and squamosal? Image has been corrected for perspective from the original posted photo. That’s the left femur in the teeth.

Padian (2009) wrote that Wiman (1925) noted, “the bones of the left side of the skull behind the premaxilla are missing, so that one sees the posterior part of the skull from inside the right side.” Padian also considered the squamosal missing but made few comments about the skull other than the teeth and jaw symphysis, the most easily seen elements. He did not comment on the palate or occiput elements, which are more difficult to determine.

Figure 3. Click to enlarge. Digital Graphic Segregation applied to the skull revealing the location of the displaced postorbital and palatal elements. Note much of the left maxilla is missing, revealing the right maxilla in medial view. Look closely to see the replacement tooth coming up laterally on the longest dentary tooth.

DGS Step-by-step
Digital Graphic Segregation helps one understand crushed fossils by removing areas of chaos and segregating bones by color and layer. Coloring the easy bones first ultimately reveals the difficult ones. And that’s the beauty of it. Later, making a reconstruction of the elements lifted and placed digitally, confirms the fit of the rest.

The parietal lateral elements were broken off and slightly displaced. The postorbital lay inside the jugal (Fig. 3). I would be surprised if the palatal elements have ever been identified. They are currently folded up in the parasagittal plane. The major elements of the occiput are probably washed away along with the left side of the skull.

Figure 4. Dorygnathus R156 reconstructed in three views. Elements from the insitu image were lifted intact and reassembled here in the second phase of DGS. A reconstruction confirms the identification of the elements as the puzzle pieces fit back together in patterns that resemble sister specimens. There were probably more dentary teeth, but the present view (Fig. 3), taken from slightly below. does not reveal them.

Phylogenetic analysis
The original reconstruction was refined by the new reconstruction (Fig. 4), but only two or three traits changed scores in the large pterosaur tree. The result of these rescorings nested R156 with Sericipterus, which it nested next to previously.

Figure 5. Doryganthus UUPM R156 revised with new data coming from the online image in high resolution of the skull and cervicals. Science marches on.

The nearly parallel pterygoids are atypical for pterosaurs in general, but become even more parallel in ctenochasmatids. R156 is in the lineage of ctenochasmatids according to the large pterosaur tree, something that should be obvious from its similarly protruding teeth. A while back those teeth were the first clues I had of a possible direct ancestry with ctenochasmatids. Later, by adding taxa, I realized that the tiny pre-ctenochasmatids transitioned larger forms like Angustinaripterus to Ctenochasma.

Figure 6. The Vienna specimen of Dorygnathus portrayed in Wiman 1925, which, ironically, is a study of the R156 Uppsala specimen, not the Vienna specimen shown here. The R156 specimen was not illustrated by either Wiman or Padian.

Wiman (1925) likewise did not figure the R156 skull
Like Padian (2009), Wiman (1925) did not illustrated the the R156 skull. Instead Wiman employed the Vienna specimen skull, after Arthaber. Compared to figure 3, several of the suture differ here, perhaps attributable to a more primitive knowledge of the pterosaur skull back in 1925. No known pterosaur has such a large quadratojugal, nor such an oddly shaped jugal.

References
Andres B, Clark JM and Xing X 2010. A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs, Journal of Vertebrate Paleontology 30: (1) 163-187.
Padian K 2009. The Early Jurassic Pterosaur Dorygnathus banthenis (Theodori, 1830) and The Early Jurassic Pterosaur Campylognathoides Strand, 1928, Special Papers in Paleontology 80, Blackwell ISBN 9781405192248
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs, London (Salamander Books Ltd)192 pp.
Wiman C 1925. Über Dorygnathus und andere Flugsaurier. Bulletin of the Geological Institute of Uppsala, 19 (for 1923), 23–54.

wiki/Dorygnathus
wiki/Sericipterus

Turtles and Eunotosaurus, rib comparisons – Lyson et al. 2013

Lyson et al. (2013) recently homologized the odd ribs and vertebrae of Eunotosaurus with those of turtles (Fig. 2) and nested Eunotosaurus with turtles as the sister taxa of pareiasaurs (Fig. 1).

Figure 1. From Lyson et al. (2013) in which turtles nest with Eunotosaurus and pareiasaurs. Light orange taxa are suprageneric. Green boxes highlight nodes that are different from the large reptile tree.

Lyson et al. (2013) reported, “The goal here is not an exhaustive description of Eunotosaurus but rather one focused on shell related features and novel morphologies not apparent in previous descriptions. A more comprehensive treatment will be provided in a later publication.”

To their point, the expanded dorsal ribs of Eunotosaurus and Odontochelys are remarkably similar and T-shaped in cross-section. Unfortunately, the large reptile tree, which relies on no suprageneric taxa and includes a much larger number of pertinent taxa, found Eunotosaurus nested with Acleistorhinus (in Fig. 1 separated by 3 nodes in Lyson et al) and then Milleretta (in Fig. 1 separated by an additional node in Lyson et al).

Lyson et al. (2013) based their analysis on deBraga and Rieppel (1997), which relies heavily on suprageneric taxa, which always brings problems (like nesting gliding kuehneosaurs as sisters to swimming sauropterygians in figure 1). To their credit, Lyson et al. (2013) nested pareiasaurs and turtles as Milleretta descendants. Lyson et al. (2013) listed diadectids as outgroups outside the Reptilia along with Seymouriadae. As reported before, diadectids are basal reptiles, not amphibians.

Figure 2. Eunotosaurus compared to Odontochelys. While remarkably alike in many respects, especially with regard to the dorsal ribs, the large reptile tree nested these two widely separated. The long toes, long tail and slender limbs of Eunotosaurus were inherited from Milleretta ancestors and they both share a lateral temporal fenestra. Taxa must always be considered in toto, not just on the basis of their ribs.

We looked at Lyson et al. (2010) earlier here, in which they nested Eunotosaurus with turtles. Unfortunately in the large reptile tree moving Eunotosaurus to the base of turtles  adds 144 steps.

Figure 3. Skull of Eunotosaurus compared to turtles, Milleretta and Stephanospondylus. The odd bedfellow here in Eunotosaurus, which retains the lateral temporal fenestra of its Milleretta (RC14) ancestors.

Comparing turtle skulls to turtle ancestor candidates (Fig. 3) graphically demonstrates the differences that put Eunotosaurus as the odd man out.

We don’t know what the ribs of Stephanospondylus or Milleretta (RC70) look like. Thankfully there is no such thing as modular evolution. Rather phylogenetic bracketing hints that these two likely had broad ribs too, but then… pareiasaurs do not have such broad ribs. And, Odontochelys does not have transverse processes, but Proganochelys does. So…we’ll have to wait for that data.

References
DeBraga M and Rieppel O 1997. Reptile phylogeny and the affinities of turtles. Zoological Journal of the Linnean Society 120, 281–354.
Lyson T, Bever GS, Scheyer TM, Hsiang AY and Gauthier JA 2013. Evolutionary Origin of the Turtle Shell.

Where are the internal nares in plesiosaurs?

Figure 1. Simosaurus and Anningasaura. Somewhere between these two the internal and external nares of these protoplesiosaurs became much smaller, almost useless vestiges. With such a tiny nostril in Anningsaura, apparently breathing continued through the mouth alone. The placement of the internal nares did not shift much. Is that a secondary choana (internal naris) between the pterygoids? Probably not because it’s not much larger than the real choana, so no advantage. There is no medial extension of the maxilla here as in other reptiles with a secondary palate (see below).

The recent paper on pliosaur palates by Schumacher et al. (2013) considered the placement of the internal nares in plesiosaurs (Figs. 1, 3). They noted Buchy et al. (2006) questioned the various placements and offered evidence for a functional secondary palate in plesiosaurs, shifting the internal nares to the back of the palate, posterior to the pterygoids, similar to the situation in crocodilians (Fig. 2). However in crocs, as you can see, the maxillae and palatines contact medially producing a standard sort of secondary palate.

Figure 2. The palate of Alligator. Note the posterior placement of the internal nares with paired maxillae, palatines and pterygoids forming the secondary palate.

The traditional view
holds that a pair of very small openings in the anterior half of the plesiosaur palate (Figs. 1,3), anterior to the palatines, represent the internal nares through which respiration took place.

Another traditional view
Williston (1903) accepted such a position for Dolichorhynchops, but not for Brachauchenius. Instead, despite the retention of internal nares in the traditional place, Williston placed the internal nares between the pterygoids separated by the parasphenoid (see Plesiosaurus in figure 3) as in crocodilians.

More recently, Schumacher et al. (2013) reported, “We have independently concluded that the posterior interpterygoid vacuity…should be called the internal nares.”

The Schumacher Hypothesis
Such a posterior position of the internal naris would be due to the development of a secondary palate in plesiosaurs, according to Schumacher et al. (2013). Benefits: Shifting the internal nares posteriorly, as in crocodiles, separates nasal respiration from oral functions (like biting, chewing, reorienting and swallowing). Problems: Small nares restrict air passage and ventilation. Since the posterior openings are typically slightly larger than the anterior ones Schumacher et al. (2013) suggest that the shift was made by soft tissue within the skull and the tiny anterior openings would have been covered with mechanosensory or chemosensory tissue, thereby completely blocking respiration there. According to Schumacher et al. (2013) respiration would then have taken place at the back of the palate where the slightly larger interpterygoid opening is.

Figure 3. Click to enlarge. Enaliosaur palates beginning with Claudiosaurus (upper left). The internal nares shrink in Anningasaurus, Pisotosaurus and Plesiosaurus compared to Simosaurus and Pachypleurosaurus. The palate is open posteriorly only in Plesiosaurus, but that does not appear to be a channel for respiration.

Figure 4. Sea turtle with secondary palate. Here the palatines join medially to shelve the respiratory tract and shifting the internal nares to mid palate. From Brown and Madara 2000. See Proganochelys for a turtle without a secondary palate.

Of course
All that presupposes that plesiosaurs actually breathed through those tiny nostrils and internal nares. Maybe they didn’t. Maybe, once the nares became sufficiently tiny (vestigial), plesiosaurs began to breathe through their mouth, like the sea turtle in figure 5. This makes all the more sense in hyper-long-necked elasmosaurs, as the mouth offers no respiratory restrictions while elevating the skull above the water surface (even slightly above as in fig. 5). This also makes sense in giant-jawed pliosaurs where breathing might have taken place with the jaws just barely open and air respiring between the slightly gaped giant teeth, perhaps while “spy-hopping,” or during less obvious maneuvers.

Figure 5. Sea turtle breathing at the surface. Both the nares and the mouth are open. (Photo by Joe Raedle/Getty Images)

Phylogeny Clues
If we look at a series of plesiosaurs and their ancestors (Fig. 6) we see that Claudiosaurus, with its tiny skull, had the relatively largest internal nares. The nothosaurs (Pachypleurosaurus, Lariosaurus, Simosaurus (Fig. 1) had a smaller, but still substantial internal naris. In contrast, Anningasaura and Pistosaurus had vestigial internal nares, obviously unusable for respiration. Other marine taxa (Fig. 3) also had tiny internal nares.

Something changed.
Between Simosaurus and Anningasaura both the internal and external nares shrank to vestiges (Fig. 1). I think it’s likely that Anningasaura and its plesiosaur and pliosaur descendants were breathing through their mouth.

Figure 6. Secondary palate development in a series of synapsid cynodonts leading to mammals. In  the eutheriodont and Procynosuchus the secondary palate is incomplete. In Thrinaxodon and all subsequent cynodonts, including all mammals, the secondary palate is complete when the maxillary palatal processes meet each other along with the palatine palatal processes. Note the gradual posterior shift of the internal naris from Thrinaxodon to Morganucodon. Image from Hopson 1991.

In a real secondary palate,
as in synapsids (Fig. 6), the development of a secondary palate (maxillae and palatines meet medially) can be traced through a series of fossils. The same holds true for crocodilians (Fig. 2, see Scleromochlus and Terrestrisuchus for taxa without a palate), sea turtles (see Proganochelys for a taxon without a palate) and pterosaurs (Fig. 7, see Cosesaurus for the primitive condition). Champsosaurus doesn’t have a secondary palate, just a longer snout and the internal nares stayed put.

Figure 7. Click to enlarge. Evolution of the pterosaur palate from Eudimorphodon to Pterodaustro. The secondary palate formed by maxillary palatal processes meeting at the midline shift the internal nares posteriorly. A similar expansion of the maxillae and migration of the internal nares is not documented in sauropterygians.

Sauropterygians do not document a similar gradual shift of the internal nares. Rather the nares simply shrinks reflecting a lack of usage while shifting to respiration through the mouth. There is no medial extension of the maxilla or palatine. Various valves would have been present to open and shut the esophagus (to the stomach) and epiglottis (to the lungs). Otherwise, no bony changes document the development of a secondary palate as in other reptiles (contra Schumacher et al. 2013). And there’s no real benefit to that marginally larger interpterygoid opening. The presupposition that the nares were used for breathing is at the heart of the problem. The problem goes away when that supposition goes away.

References
Buchy M-C, Frey E and Salisbury  2006. Internal cranial anatomy of Plesiosauria (Reptilia, Sauropterygia): evidence for a functional secondary palate. Lethaia 39:290-303.
Hopson JA 1991. Systematics of the nonmammalian Synapsida and implications for patterns of evolution in synapsids, in H-P Schultze & L Trueb [eds], Origins of the Higher Groups of Tetrapods: Controversy and Consensus. Comstock, pp. 635-693.  Schumacher BA, Carpenter K and Everhart MJ 2013. A new Cretaceous Pliosaurid (Reptilia, Plesiosauria) from the Carlile Shale (middle Turonian) of Russell County, Kansas. Journal of Vertebrate Paleontology 33(3):613-628.

Obvious sexual dimorphism in pterosaurs?

Figure 1. From Tetrapod Zoology with this caption, “Cover of TREE featuring Knell et al. (2012). Image (featuring male and female Pteranodon with obvious sexual dimorphism) by Mark Witton.” Naish’s statement has been shown to be false. Attention to detail and rigorous phylogenetic testing provides other results (Fig. 2) in which these two inaccurately portrayed Pteranodon specimens actually represent distinct species. In general, smaller skulls with smaller crests are phylogenetically closer to the ancestral germanodactylids with smaller skulls and smaller crests. Not only does that make sense, it can be demonstrated phylogenetically (Fig. 2). See the juvenile? Cute, but inaccurate. (see below).

An April post at Darren Naish’s Tetrapod Zoology was headlined, “Dinosaurs and their ‘exaggerated structures’: species recognition aids, or sexual display devices?” (refs below).

Naish wrote, “Our latest paper is devoted to a discussion of the species recognition hypothesis and, specifically, why we think it’s problematic and should be discarded. We’ve noted that dinosaur workers have increasingly taken to mentioning species recognition whenever they discuss exaggerated structures (see list of citations in Hone & Naish 2013), so now is a good time to try and set the record straight.”

Figure 2. Click to enlarge. A family tree of Pteranodon and Nyctosaurus derived from Germanodactylus. Note the size increase is gradual. So is the crest size increase. Of all these many specimens, can you tell which are male and which are female? I can’t. There are no two skulls, sans crests, that are identical in morphology. You can’t divide this set of illustrations into two genders, and yet, according to Naish you should be able to. Attention to detail indicates there’s also much more to skull morphology than crest shape.

Is it possible to ascertain that small crested specimens are females?
Or are small crested specimens just in the lineage of large crested specimens? Contra Naish, species recognition helps us identify various dinosaurs with all their crests, horns and feathers. The same is true of pterosaurs and you can test this with phylogenetic analysis (Fig. 2). If this was gender identification in Pteranodon, there should be just two forms relatively close to one another for each of the above skulls. But no two here are even that much alike. Instead they form a series of gradually evolving shapes, which defines them as distinct individuals and species. Interestingly, there is a derived size decrease in specimens R, S, T and Z4.

Juvenile Pteranodon
The image in figure 1 also shows a juvenile Pteranodon with an appropriately short crest and short beak. Well, we have a juvenile Pteranodon (Fig. 2) and it doesn’t have any indication of a short beak, but retains the proportions of an adult, and a specific adult at that, YPM 2594, which is likewise known from a posterior skull without a complete rostrum.

Pteranodon is the Cretaceous equivalent of Darwin’s finches.
Rapid diversification in Pteranodon originated as individual variation that was enhanced over the generations by natural selection. Pteranodon was not just one or two species, but dozens, as is plainly evident when you look at dozens all once (Fig. 2). That’s the value of accurate reconstruction, something most pterosaur workers avoid like the flu.

Getting back to sexual dimorphism
Naish wrote, “And we absolutely reject Padian & Horner’s (2013) argument that sexual dimorphism is essential for the recognition of sexual selection: there’s unambiguous evidence from the living world that sexual selection is at play even when dimorphism is absent (Hone et al. 2012, Knell et al. 2012, 2013).”

To Naish’s point, there is always sexual dimorphism, whether presented in skeletal differences, beards, breasts, genitals, feathers or pheromones. Sometimes it’s more obvious. Sometimes less. In pterosaurs no one has ever been able to document male vs female differences in the skeleton, even when there’s an egg between the legs of an obvious female, a subject we looked at earlier. Males, as best as we can ascertain were outwardly identical. Crests appeared on various darwinopterids during speciation, as we looked at earlier. Some have even been named new genera by various workers.

Unfortunately, at least in pterosaurs,
there’s no evidence for gender identification that can stand up under the scrutiny of phylogenetic analysis. We don’t see only two kinds of Pterodactylus. We see several (with not one tested specimen identical to another). We don’t see only two kinds of Rhamphorhynchus. We see dozens. Lack of reconstructions and lack phylogenetic analysis leads paleontologists like Darren Naish into supposition and assumption. What’s “obvious” to him is only obvious because he hasn’t tested it to see if it is indeed true. Testing, not supposition, is what makes good Science.

And by the way,
Naish and those who are in his camp are among those who think (without testing) that tiny pterosaurs are juveniles of larger taxa. Bennett (2006) made this supposition, but his study did not stand up to phylogenetic analysis.  Tiny Solnhofen pterosaurs of all sizes and shapes nest at the bases of several major clades and are the transitional taxa from one clade to another as each phylogenetic series gradually decreases then increases in size.

Darren Naish and Modular Evolution
Naish wrote,  ”So it’s almost as if the head and neck were evolving at different rates from the rest of the body: in other words, Darwinopterus looks like a classic case of ‘mosaic evolution’ or modularity (hence the species name). This much-discussed evolutionary phenomenon has been considered controversial, in part due to a lack of good examples: Darwinopterus looks like one of the best yet discovered, and this isn’t lost on Lü et al. (2009).”

A lack of good examples indeed! This hypothesis applies only to Darwinopterus in order to cover up a lack of good phylogenetic analysis, which you can see here.

Of course, there’s no such thing as “modular evolution,” made famous during the Darwinopterus bungle, but Naish embraced this fairy tale without criticism. If true we’d see it on other taxa and in other clades, but we don’t It was invented for Darwinopterus. If modular evolution were true we’d have less confidence in our reconstructions of partial skeletons because heads would be evolving leaving the legs far behind, as imagined for Darwinopterus. In reality the palate evolves along with the toes and everything else. In reality Darwinopterus is a dead end taxa leaving no known descendants, but it did convergently evolve a large skull and smaller naris. Phylogenetic analysis settles that issue.

That being said…
There’s much more in Naish’s blog that is good Science and worth considering. If interested, follow this link. He’s just got an Achilles heel when it comes to pterosaurs.

So, there’s more to Pteranodon that just size and crests.
We know of a variety of post-crania as well, some robust and some gracile with various humerus shapes (Fig. 3). Only a few Pteranodon specimens are known from associated skulls and post-crania. So, which post-crania go with which crania? We can only guesstimate now and earlier some effort was made toward this goal. Small ones might have been young or might have been primitive (more likely the latter, since juveniles, like Ptweety or so rare and the small ones are not virtually identical to any large ones (isometric growth).

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

If Naish is right
and there is “obvious” sexual dimorphisim in Pteranodon, let him (or someone!) present three or four pairs of males and females, then subject them to phylogenetic analysis. The gender pairs should match with their mates if true.

And finally, we need to talk about the “female” pelvis in Pteranodon.
It’s morphologically closer to Nyctosaurus as reported here. And, yes, it’s a big pelvis, but we have further evidence of Pteranodon-sized Nyctosaurus, because the former fused the extensor tendon process and the latter did not, as reported here , and we know of a very larger unfused extensor tendon process on what others have identified as a Pteranodon based on its size.

No matter what crap they throw*,
I’m not going to let Naish and Witton disfigure and fantasize pterosaurs when good solid evidence is available to counter their traditional and mistaken hypotheses. Credit will also be given when appropriate.

* By “crap,” I mean blackwashing statements that contain no pertinent specifics or evidence. You’ll know them when you see them.

References
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.SMNS
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Knell R, Naish D, Tompkins JL and Hone DW E 2012. Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution28, 38-47.
Naish D and Cuthill IC 2012. Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia 45, 139-156.
Naish D, Tomkins JL and Hone DWE 2013. Is sexual selection defined by dimorphism alone? A reply to Padian and Horner. Trends in Ecology and Evolution. http://dx.doi.org/10.1016/j.tree.2013.02.007

Odontochelys: not a turtle. Not even a turtle ancestor. Close, but no cigar.

Odontochelys was hailed as the most primitive known turtle…
…a turtle with teeth. It had a plastron (lower shell), but no carapace (upper shell). It also had more toe phalanges than turtles do. So, all in all, Odontochelys made a pretty good, but somewhat unexpected ancestral turtle.

From the Li et al. (2008) abstract:
“The origin of the turtle body plan remains one of the great mysteries of reptile evolution. The anatomy of turtles is highly derived, which renders it difficult to establish the relationships of turtles with other groups of reptiles. The oldest known turtle, Proganochelys from the Late Triassic period of Germany, has a fully formed shell and offers no clue as to its origin. Here we describe a new 220-million-year-old turtle from China, somewhat older than Proganochelys, that documents an intermediate step in the evolution of the shell and associated structures.”

Actually …
Turtles provide hundreds of clues to establish their relationships with other groups of reptiles. You just have to include the right taxa and do the work, like Lee (1993) and the large reptile tree did.

Topology change
The following results reflect a topology change inthe large reptile tree moving pareiasaurs from diadectids to millerettids. The millerettid/caseid clade was always the weakest link in the tree. Now it is stronger after this correction.

Turtle traits shared: 
There’s no doubt that Odontochelys is very close to actual turtles. Odontochelys shares several traits with Proganochelys to the exclusion of all known close kin. Note these are all post-cranial and include:

1. Skull shorter than cervicals
129. Number of cervicals: eight
129. Cervical centra longer than tall
135. Cervical rib: stub (unknown in Milleretta and Stephanospondylus)
142. Lumbar ribs not reduced
144. Two sacral ribs
159. Plastron
165. Scapula rod-like (but without the acromion process in Odontochelys.)
174. Manual 1.1 aligns with mc2 and mc3
196. Femoral head subrectangular and offset
207. Longest metatarsal: three
208. Metatarsal 1 less than half of mt3
214. Longest pedal digit three (unknown in Milleretta and Stephanospondylus)
215. Metatarsals 2-3 align with p1.1
216. Pedal 4 digit subequal to metatarsal 4 (unknown in Milleretta and Stephanospondylus)
217. Pedal digit 4 phalanges: 2 (unknown in Milleretta and Stephanospondylus)
220. Pedal digit 4 narrower than 3
(numbers are characters in the large reptile tree)

10 dorsal vertebrae for Proganochelys, 9 for Odontochelys
Broad flat dorsal ribs for both.

Figure 1. Click to enlarge. The skulls of (left to right) the RC70 specimen of Milleretta, Odontochelys, Stephanospondylus and Proganochelys. The two on the left belong to a distinct clade and the two on the right belong to a distinct clade along with pareiasaurs. Odontochelys is more closely related to this specimen of Milleretta than to Stephanospondylus and Proganochelys.

Odontochelys problems
In the large reptile tree the outgroup for Proganochelys remained Stephanospondylus and the Pareiasauria, all of which had anterior nares. In contrast, Odontochelys had an elongated anterolateral naris, a more primitive trait. So, it didn’t quite fit. And there’s more…

Figure 2 Odontochelys palate compared to Proganochelys, Anthodon and Milleretta RC70. The lateral palate of Odontochelys is grey because it is covered by mandible or missing from the two specimens, but the transverse pterygoids tell the tale. Turtles and pareiasaurs share an anteriorly directed pterygoid and medially directed nares.

Over the last few days I did my homework 
and the results of the new reconstruction and phylogenetic analysis revealed a new relationship. According to the results of phylogenetic analysis in the large reptile tree the RC70 specimen of Milleretta is closer to Odontochelys. Stephanospondylus and the Pareiasauria are closer to Proganochelys. All shared a common ancestor that probably greatly resembled the RC70 specimen of Milleretta. That means Odontochelys attained all of its turtle-like traits by convergence, not direct ancestry. Earlier we looked at several other turtle-like reptiles and mammals. Now we have one more in Odontochelys.

Figure 3. Odontochelys in ventral view (below) and dorsal ribs (above). It looks like a perfect turtle ancestor, by phylogenetic analysis indicates it is not a turtle ancestor, but a cousin.

Traits that separate Odontochelys from Proganochelys.
The following traits are shared by the RC70 specimen of Milleretta and Odontochelys but not found in Proganochelys and Stephanospondylus (and pareiasaurs where not preserved in Stephanospondylus):

4. Skull table concave
8. Snout constricted
9. Prefrontal postfrontal separated
11. Nasal widest at mid length
13. Lateral rostral shape straight angled
14. Premaxilla horizontal
22. Naris opening anterolateral
43. Prefrontal maxilla no contact
45. Frontals with posterior processes
48. Postparietals angled dorsally
57. Frontal nasal angle: zigzag
65. Quadrate not concave
68. Quadratojugal essentially straight
73. Quadrate posterior lean
78. Supraoccipital broader than exoccipitals
79. Opisthotic lateral without fenestrae
84. Postorbital extends to minimum medial parietal
92. Internal nares lateral
93. Interal nares parallel maxilla
94. Suborbital fenestra absent
100. Parasphenoid teeth present
101. Pterygoid transverse process shagreen of teeth
104. Pterygoid lateral edge sharp angle
105. Pterygoid broad triangle
122. Dentary contributes to coronoid process
128. Mandible ventrally straight
139. Dorsal transverse process not transversely longer than centrum width
141. Caudal transverse processes absent beyond #8
156. Cleithrum present
160. Clavicle shorter than scapula
161. Scapula coracoid not fused
176. Longest manual digit: 3 and 4
178. Manual digit four phalanges: four
183. Ilium anterior process absent
188. Pubis orientation medial
190. Acetabulum ventrally deflected
198. Fourth trochanter sharp
199. Tibia not shorter than 2x ilium width
203. Non-fenestrated tarsus (some fused)
204. Tarsal less than 0.6 pes length
219. Pedal 2.2 is a non-ungual.
227. Dorsal body osteoderms absent
228. Overall size: not greater than 30 cm tall, 60 cm long

Same list, opposite perspective
These are traits found in Proganochelys and Stephanospondylus (and or pareiasaurs), but not in Odontochelys and Milleretta.

4. Skull table flat
8. Snout not constricted
9. Prefrontal postfrontal contact
11. Nasal parallel sides
13. Lateral rostral shape convex angled
14. Premaxilla transverse
22. Naris opening anterior
43. Prefrontal maxilla contact
45. Frontals withoutt posterior processes
48. Postparietals onon dorsal plane or absent
57. Frontal nasal angle > 45º
65. Quadrate concave
68. Quadratojugal fused to squamosal
73. Quadrate curls posteriorly
78. Supraoccipital not broader than exoccipitals
79. Opisthotic lateral with fenestrae
84. Postorbital does not extend to minimum medial parietal
92. Internal nares medial with wide vomer
93. Internal nares deflected medially
94. Suborbital fenestra present
100. Parasphenoid teeth absent
101. Pterygoid transverse process edentulous
104. Pterygoid lateral edge smooth curve
105. Pterygoid inverted triangle
122. Dentary does nto contribute to coronoid process
128. Mandible ventrally concave then convex
139. Dorsal transverse process transversely longer than centrum width
141. Caudal transverse processes present beyond #8
156. Cleithrum absent
160. Clavicle as tall as scapula
161. Scapula coracoid fused
176. Longest manual digit: 2 and 3
178. Manual digit 4 phalanges: fewer than 4
183. Ilium anterior process small
188. Pubis orientation angled ventrally
190. Acetabulum lateral
198. Fourth trochanter absent
199. Tibia shorter than 2x ilium width
203. Fused astragalus/calcaneum
204. Tarsal not less than 0.6 pes length
215. Metatarsals 1-3 align
217. Pedal digit 4 phalanges: 4
219. Pedal 2.2 is absent (or pedal 2.2 is an ungual.)
227. Dorsal body osteoderms present
228. Overall size: greater than 30 cm tall, 60 cm long

Turtle mimics
Earlier we looked at several taxa that mimic turtles, more or less, and their shells. None of them are turtle ancestors or kin. Odontochelys is very, very close to that ideal ancestor, but it had many of those traits by convergence. At this point, there are no descendants known for Odontochelys.

Similarly,
Eunotosaurus was less close to that ideal, yet derived from a sister to another specimen of Milleretta (RC14). So, we see natural selection at work trying to build a turtle shell twice within a short phylogenetic distance before nature finally got it right in the ancestors of modern turtles. It’s just a shame that so many sister taxa are known only by their skull and scraps, but that’s what phylogenetic analysis is all about.

Numbers
In MacClade, moving Odontochelys to nest with Proganochelys adds 18 steps. Moving Odontochelys + Milleretta (RC70) to nest with Proganochelys adds 6 steps. Moving Milleretta (RC70 to Proganochelys adds 19 steps. Moving Odontochelys + Milleretta (RC70) to the base of turtles + pareiasaurus adds 5 steps. So, the relationships are indeed very close, but no cigar. Odontochelys is not an official turtle. Or a turtle ancestor.

Think of Odontochelys as the enantiornithine turtle.
It really looks like a turtle, but it evolved convergently, or in parallel.

Li et al. (2008) analysis
They reported, “To test the position of turtles amongst reptiles in general, we included Odontochelys in the data matrix of Rieppel and Reisz (1999).” They rooted their analysis on an all-zero hypothetical ancestor and on Seymouridae and Diadectomorpha. Both results had only one or tree most parsimonious trees. Odontochelys came out as a sister to Testudines and the two formed a clade, the sister of Sauropterygia within Lepidosauromorpha. Ugh. We learned earlier from our turtle/pterosaur nesting within the new Archosauromorpha that there is an attraction to the pachypleurosaurs within that list. But the large reptile tree nests sauropterygia far from the lepidosaurs when the inclusion list is expanded. Readers are also aware of the the turtles are owenettids vs. turtles are placoderms vs. turtles are pareiasaurs controversy discussed online here.

Regarding the carapace
Li et al. (2008) reported, “Odontochelys provides documentation that in turtles, the plastron evolved before the carapace.” Maybe not. Now that Odontochelys is not an official turtle, the hypothesis put forth by Lee (1993) on the origin of turtle scutes from pareiasaur scutes comes back to the forefront.

Now we also know where pareiasaurs came from
Earlier the large reptile tree indicated that pareiasaurs were derived from similarly bulky procolophonids and diadectids.  Now pareiasaurs descend  from a sister to Milleretta (RC70), bulking up via a sister to Stephanospondylus. Apparently the cheek plates flared out afterwards in pareiasaur ancestors. We’ll add details in a future post on pareiasaur origins.

References
Lee MSY 1993. The origin of the turtle body plan: bridging a famous morphological gap. Science 261, 1716–1720.
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.
Layson TR, Bever GS, Bhullar B-AS, Joyce WG and Gauthier JA 2010. Transitional fossils and the origin of turtles. Biology Letters June 9 2010. doi: 10.1098/rsbl.2010.0371
Rieppel O and Reisz RR 1999. The origin and early evolution of turtles. Annu. Rev. Ecol. Syst. 30, 1–22.

wiki/Odontochelys

Therapsids 1982 – A Tribute To Artist Mark Hallett

When I turned to this page in Science Digest, November 1982, my life changed. The next 30 years were largely devoted to learning more and contributing whenever possible to the science of paleontology (much to the distress of paleontologists everywhere). But enough about me. Let’s talk about the artist who designed this page, the original source of all this continuing inspiration.

Figure 1. Click to enlarge. The March of the Mammals as illustrated by Mark Hallett in the November 1982 issue of Science Digest, page 62. This fantastic image caught my eye, stirred my imagination and changed my life. The stains, tape and wrinkles attest to its importance over the last 30 years.

Figure 2. Mark Hallett at work.

This is the art of Mark Hallett
Didin’t we all learned something of great value from Mark Hallett and his work? To see his art is to behold talent, insight and technique that is sure to inspire. To see his studio, festooned with a vast menagerie of dino-things, is to think you’ve died and gone to heaven.

The above article in Science Digest (Fig. 1, Class Struggle: The Rise of the Mammal, text and illustrations by Mark Hallett) opened my eyes to a subject I had not thought much about since the days of those Marx dinosaur toys in the 1960s. Inspired by what I saw and excited by the new world that Hallett presented, I started gathering all the data I could about dinosaurs and other odd reptiles. Shortly thereafter I started putting together “Giants of Land, Sea and Air – Past and Present” and thereafter several other books and websites. Before long there were full scale dinosaurs in the garage, papers, abstracts and visits to local schools as a guest speaker. I dropped paying clients to focus on the work, and I found my passion — all because of this one gorgeous page of therapsids.

An inspiration to us all
I learned how to illustrate by trying to copy Mark Hallett’s work and there was a lot of it back then. Today Mark has his own website at hallettpaleoart.com featuring on the homepage his famous sauropod family on the mudflats (I like the narrow wings on his pterosaurs!).

Figure 3. A poster combining many of the dinosaurs from Hallett’s Zoobook: Dinosaurs. Just drink in the glory and wonder!

Figure 4. Mark Hallett’s art for the cover of a Seismosaurus book. Remember books? They are the phylogenetic ancestors of pdf files.

Hallett has has created dinosaur art for National Geographic, Disney, Universal Studios and many more, including several children’s magazines. His work for Zoobooks, Dinosaurs (1984), was my guidebook and inspiration for skin color, pose, etc. For many, including yours truly, it was an introduction to all that was new about dinosaurs.

I had the pleasure of meeting Hallett several times and always found him engaging and encouraging.

Sadly, Science Digest lasted only another four years, ceasing publication in 1986 under competitive pressure from two new science magazines, Omni and Discover. I have to confess, for those last four years I kept thumbing through Science Digest hoping to recapture that initial buzz. And now you know.

Looking toward the future
I hope others will likewise consider Mark Hallett as their virtual mentor and inspiration and take it all to the next level. I know many of you caught the same buzz.