Pelecanimimus joins the LRT

Yes, it is the basalmost ornithomimosaur,
(of three tested), but from whence did the theropod dinosaur, Pelecanimimus (Figs. 1-3), arise?

Figure 1. Rough tracing and reconstruction of Pelecanimimus based on low rez photos from 1994 paper.

Figure 1. Rough tracing and reconstruction of Pelecanimimus based on low rez photos from 1994 paper.

 

In the original paper
Pérez-Moreno et al. 1994 tested only Allosaurus, Albertosaurus, Deinonychus and Troodontidae in order of decreasing distance as outgroup taxa to Pelecanimimus + Ornithomimosauria using 22 characters. In the early days of PAUP this is all that most workers did back then… sort of testing the phylogenetic waters.

In a competing study
the large reptile tree (LRT) tests 1370+ taxa and recovers the holotype of Compsognathus as the proximal outgroup. In the same study members of the Troodontidae nest closer to birds (birds nest within the clade that includes some traditional troondontids, but not others).

Unique indeed…
The long down-curved jaws of Pelecanimimus are not found in either ancestral compsognathids nor descendant ornithomimosaurs. The wrist appears to be made of tiny bones, capable of minimal movement. ‘On the other hand’ the fingers are provided with large cylindrical joints for substantial flexion and extension.

Figure 2. DGS tracings from 1994 paper focusing on skull and manus of Pelecanimimus.

Figure 2. DGS tracings from 1994 paper focusing on skull and manus of Pelecanimimus.

A gular sac and cranial soft tissue are present
on the specimen. Not sure if we’re seeing radiating patterns of soft tissue aft of the ulna, or are those preparator chisel marks? Nothing glows in the UV image (Fig. 1), so let’s go with the latter.

Figure 4. Pelecanimimus to scale with Struthiomimus and Compsognathus.

Figure 3. Pelecanimimus to scale with Struthiomimus and Compsognathus.

References
Pérez-Moreno BP et al. (5 co-authors) 1994. A unique multi-toothed ornithomimosaur dinosaur from the Lower Cretaceous of Spain. Nature 370(4):363–367.

wiki/Pelecanimimus

A new look at Jidapterus (basal azhdarchid pterosaur)

Wu, Zhou and Andres 2017
bring us long anticipated details on Jidapterus (Early Cretaceous, Dong, Sun and Wu 2003) which was previously presented as a small in situ photograph lacking details. Even so a reconstruction could be made (Fig. 1). Coeval larger tracks (Elgin and Frey 2011) have been matched to that reconstruction.

Figure 2. Jidapterus matched to the Gansu, Early Cretaceous pterosaur tracks. The trackmaker was one-third larger than the Jidapterus skeleton.

Figure 1. Jidapterus matched to the Gansu, Early Cretaceous pterosaur tracks. The trackmaker was one-third larger than the Jidapterus skeleton.

Of interest today
is the fact that Jidapterus was originally and, so far, universally considered toothless. Its specific name, J. edentatus, refers to that condition. Wu, Zhou and Andres 2017 produced tracings (Figs. 2, 3) of the rostrum that are also toothless. However, they are crude and appear to miss the premaxilla and maxilla sutures, the palatal elements… and maybe some teeth. Those jaw rims are not slippery smooth like those of Pteranodon. Outgroups in the large pterosaur tree (LPT), all have tiny teeth.

Figure 2. Rostrum of Jidapterus (RCPS-030366CY) and traced according to Wu et al. and colorized using DGS to reveal skull sutures and possible teeth.

Figure 2. Rostrum of Jidapterus (RCPS-030366CY) and traced according to Wu et al. and colorized using DGS to reveal skull sutures and possible teeth. See figure 3 for details. What Wu, Zhou and Andres label the  “low ridge of rostrum” is here identified as the rostral margin above the palatal portion. 

The cladogram of Wu, Zhou and Andres
lacks dozens of key taxa found in the LPT that separate azhdarchids from convergent tapejarids and shenzhoupterids. In the LPT giant azhdarchids arise from tiny toothy azhdarchids once considered Pterodactylus specimens… and these, in turn are derived from tiny and mid-sized dorygnathids in the Middle Jurassic.

What Wu, Zhou and Andres label the  “low ridge of rostrum”
is here identified as the rostral margin rim at the edge of the palate.

Figure 3. Focus on the rostral tip of Jidapterus shown in figure 2. Are these teeth?

Figure 3. Focus on the rostral tip of Jidapterus shown in figure 2. Are these teeth? You decide. I present the data. 

As in all pterosaurs
each premaxilla of Jidapterus has four teeth according to this data.

Are these tiny teeth?
Or are they tiny occlusions and/or chisel marks. Let’s get even better closeups to figure this out. Phylogenetic bracketing indicates either tiny teeth or edentulous jaws could be present here.

References
Dong Z, Sun Y and Wu S 2003. On a new pterosaur from the Lower Cretaceous of Chaoyang Basin, Western Liaoning, China. Global Geology 22(1): 1-7.
Elgin and Frey 2011. A new azhdarchoid pterosaur from the Cenomian (Late Cretaceous) of Lebanon. Swiss Journal of Geoscience. DOI 10.1007/s00015-011-0081-1
Wu W-H, Zhou C-F and Andres B 2017. The toothless pterosaur Jidapterus edentus (Pterodactyloidea: Azhdarchoidea) from the Early Cretaceous Jehol Biota and its paleoecological implications. PLoS ONE 12(9): e0185486.

wiki/Jidapterus

The last teeth seen in hard-shell turtles

The ancestors of turtles had teeth.
You can clearly see them in Elginia (Newton 1893; Fig. 1), Sclerosaurus (Meyer 1859) and even in the basalmost soft-shell turtle, Odontochelys (Li et al. 2008). What we’re missing is a set of teeth in the basalmost hard-shell turtle in the large reptile tree (LRT, 1050 taxa), Meiolania (Owen 1886, Gaffney 1983). So we go looking for them (Fig. 1). 

Figure 1. Palates of Elginia (from Newton 1893) and Meiolania (from Gaffney 1983). Although the drawing at lower right erases them, the photo at upper right seems to show some tiny teeth and tooth sockets.

Figure 1. Palates of Elginia (from Newton 1893) and Meiolania (from Gaffney 1983). Although the drawing at lower right erases them, the photo at upper right seems to show some tiny teeth and tooth sockets.

And there they are.
The jaw rims of Meioliania appear to have tiny, useless teeth. These were overlooked or avoided by Gaffney 1983 who eliminated those tiny bumps and holes in his drawing (Fig. 1). In the era before software generated cladograms, Gaffney did not consider Meiolania the basalmost hard-shell turtle, but in the modern era, the LRT does.

When you evolve from
teeth to no teeth sometimes the tetrapod pattern seems to be

  1. relatively few big teeth, then
  2. relatively many tiny teeth, then
  3. toothlessness

The same pattern seems to play out in ophthalmosaurs and ornithomimosaurs, but not birds and mysticetes.

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.
Meyer H von 1859. 
Sclerosaurus armatus aus dem bunten Sandestein von Rheinfelsen. Palaeontographica 7:35-40.
Newton ET 1893. On some new reptiles from the Elgin Sandstone: Philosophical Transactions of the Royal Society of London, series B 184:473-489.
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

Dorsal views of basal turtle skulls support the cladogram

Earlier
here, here and here we looked at turtle origins — a controversial topic in mainstream paleontology resolved quickly and surely in the large reptile tree, which gives 639 taxa the opportunity to be ancestral to turtles.

Long story short
Toothy Elginia currently nests outside the turtles (only because we don’t have any post-crania) and toothless Meiolania nests as the basalmost turtle (Fig. 1) because it retains supratemporal horns and the elbows still extend laterally, not anteriorly. These taxa are derived from pareiasaurs, which are themselves sisters to diadectids, bolosaurs and proclophonids.

Figure 1. How the large reptile tree lumps and splits the several Diadectes specimens now included here. Note that bolosaurids, including Phonodus, now nest within other Diadectes specimens.

Figure 1. How the large reptile tree lumps and splits the several Diadectes specimens now included here. Note that bolosaurids, including Phonodus, now nest within other Diadectes specimens.

When the skulls of pertinent taxa
are seen in dorsal view (Fig. 2) it is easier to see the reduction of the horns in  pre- and basal turtle skulls. One also gets the impression that when Proganochelys and Odontochelys arrived on the scene in the Late Triassic, they both represent a much earlier radiation of turtles, both horned and not horned. So there are many more basal turtles out there waiting for us to discover them.

Figure 2. Turtles and their ancestors among the pareiasaurs. Note the soft shell turtle clade rotates the orbits until they are visible dorsally. Click to enlarge. Odontochelys is not so primitive as once considered. AND it appears to have redeveloped teeth. Note the reduction of supratemporal horns in basal turtles.

Figure 2. Turtles and their ancestors among the pareiasaurs. Note the soft shell turtle clade rotates the orbits until they are visible dorsally. Click to enlarge. Odontochelys is not so primitive as once considered. AND it appears to have redeveloped teeth. Note the reduction of supratemporal horns in basal turtles.

The Odontochelys tooth problem
Odontochelys is a Late Triassic toothed turtle that originally was considered (Li et al. 2008) a very basal turtle. Not so according to phylogenetic analysis which nests it with soft shell turtles like Trionyx. The odd thing is this soft shell turtle appears to have regrown teeth. More basal and sister taxa do not have teeth (Fig. 3). Odontochelys is also unusual in having nares in the anterior lateral orientation, not completely anterior, as in Trionyx, as in virtually all other turtles, and not dorsal, as in Ocepecephalon, which is also very off for a turtle.

Figure 3. Odontochelys and Trionyx. Note the teeth in ventral view of the Odontochelys skull.

Figure 3. Odontochelys and Trionyx. Note the teeth in ventral view of the Odontochelys skull. Click to enlarge.

The supratemporal problem
This evolutionary sequence demonstrates that the large supratemporal bones of turtles (the supratemporal horns of pre-turtles and Meiolania) have been traditionally mislabeled. This may be part of the problem that workers have had in nesting turtles in prior studies.

The molecule problem
Some researchers have found that turtle DNA is most closely matched to that of living archosaurs: crocs and birds. Everyone knows morphology does not support that nesting. Someone somewhere will figure this out someday.

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.

x

 

Tooth Loss in Turtles

An online paper by Davit-Béal, Tucker and Sire (2009) examined tooth loss in several tetrapod clades. They mentioned tooth loss in “toads in Lissamphibia, turtles and birds in Sauropsida, and baleen whales, pangolins, anteaters, sloths, armadillos and aardvark in Mammalia.” There were other extinct forms that also lost all* their teeth, including pterosaurs, certain poposaurs and other dinosaurs (ornithomimosaurs). I want to focus on turtles today.

Origins Questioned
Davit-Béal et al. (2009) wrote: The origin of turtles from ancestral sauropsids is still unclear and largely debated. Molecular data are partially congruent with morphological characters supporting diapsid rather than anapsid turtle relationships [Rieppel & deBraga, 1996deBraga & Rieppel, 1997; see Laurin & Reisz, 1995 and Lee, 1997 for Parareptilia (anapsid) turtle relationships]. However, the molecular data conflict with palaeontological data as to where exactly turtles fit within diapsids (Rieppel, 1999). Phylogenetic studies either place turtles close to the lepidosaumorphs (tuatara, snakes and lizards) (e.g.Hill, 2005) or close to the archosauromorphs (crocodiles and birds) (e.g. Hedges & Poling, 1999Iwabe et al. 2005). The turtle ancestor diverged from the other diapsids between 285 and 270 Ma (McGeoch & Gatherer, 2005) but its origin remains a mystery. The most ancient and well-known turtle is Proganochelys quenstedti (late Triassic, 220 Ma).”

 Toothlessness in turtles according to Davit-Béal et al. (2009).

Figure 1. Clicking will NOT enlarge image. Toothlessness in turtles according to Davit-Béal et al. (2009). Click to enlarge. Green lines are turtles with palatal teeth. Red lines are turtles without any teeth.

Written Just Before Odontochelys
Timing is everything and the Davit-Béal paper was likely “in press” when the Odontochelys (225 mya) paper was published (Li et al. 2008). Odontochelys is the only known primitive turtle with teeth on the rims of its jaws. Proganochelys and several other early turtles retained palatal teeth. Here the primitive diadectomorph Stephanospondylus (290 mya) is in the clade of turtles, prior to the development of the carapace and plastron 75 million years before turtles with shells.

From left to right the skulls of Stephanospondylus, Odontochelys and Proganochelys

Figure 2. From left to right the skulls of Stephanospondylus, Odontochelys and Proganochelys demonstrating tooth loss and other skull traits.

Notes from Davit-Béal (2009) 
Davit-Béal et al. (2009) reported, “P. quenstedti was roughly similar to the species that live today, except for, among other characters, the presence of several rows of conical teeth on the vomers, palatines and pterygoids (Fig. 6D), which make it unique among Testudinata as the other ancient turtles lack these teeth (Joyce, 2007). The maxilla, pre-maxilla and dentary are edentulous but the pre-maxillary has tooth vestiges (Kordikova, 2002). Although the common ancestor of all living turtles was aquatic, the earliest turtles clearly lived in a terrestrial environment (Joyce & Gauthier, 2004Scheyer & Sander, 2007).  As suggested for birds, the presence of a keratinized beak that was efficient for food uptake probably relaxed the functional pressure on teeth, which were probably lost through a similar process to that described in birds (see above). In the turtle’s ancestor, as in the bird’s ancestor, the beak minimized the negative consequences of tooth loss. In turtles, teeth were retained on the palate longer than in jaws. Teeth were lost in the vomers and palatines first, then later on the pterygoids.”

Stepping Back in Time and Phylogeny
The present tree indicates that a sister to Orobates and Diadectes preceded Stephanospondylus and Arganaceras was a basal pareiasaur sister. These taxa are widely considered to be herbivores. The 16 teeth in the left premaxilla (4) and maxilla (12) of Orobates were larger anteriorly and the tooth row ended below the mid orbit. The 15 to 21+ teeth in the left premaxilla and maxilla of Diadectes followed these patterns, but were smaller overall. The sisters Oradectes and Silvadectes were not much different.

Stephanospondylus Teeth
Romer (1925) illustrated 27 teeth in the premaxilla (3) and maxilla (24) of Stephanospondylus extending posteriorly beyond the mid point of the orbit. Each tooth had a smaller diameter but a longer length.

Odontochelys Teeth
In the one and only known toothed turtle (Li et al. 2009) 6 teeth were in the premaxilla and 18 in the maxilla. Distinct from Stephanospondylus, the premaxillary teeth were smaller than the maxillary teeth. Instead of four, there were six premaxillary teeth. The maxillary teeth started off small anteriorly, but were larger posteriorly and extended behind the orbit. As in Stephanospondylus the first maxillary tooth was slightly larger than the others.

Summary
Smaller and an increased number of teeth often precede the complete loss of teeth, as seen here in turtles. Herbivores often lose their teeth, as seen here in turtles. Turtle ancestors provide one of the few examples of herbivores that became insectivores and piscivores. Perhaps they were always omnivores. Like birds, early turtles developed a shearing keratinous beak, providing a substitute for teeth. They have no other similarities that I know of and must have developed beaks for distinct reasons.

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
Baur G 1887. On the phylogenetic arrangement of the Sauropsida: Journal of Morphology, v. 1, n. 1:93-104.
Davit-Béal T, Tucker AS and Sire J-Y 2009.
 Loss of teeth and enamel in tetrapods: fossil record, genetic data and morphological adaptations. Journal of Anatomy 2009 April; 214(4): 477–501. doi:  10.1111/j.1469-7580.2009.01060.x
Gaffney ES 1990. The comparative osteology of the Triassic turtle Proganochelys, Bull. Am. Mus. Nat. Hist. 194: 1–263.
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
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.
Romer AS 1925. Permian amphibian and reptilian remains described as Stephanospondylus. Journal of Geololgy 33: 447-463.
Stappenbeck R 1905. Uber Stephanospondylus n. g. und Phanerosaurus H. v. Meyer: Zeitschrift der Deutschen Geologischen Gesellschaft, v. 57, p. 380-437.

wiki/Proganochelys
wiki/Odontochelys

What is Lotosaurus?

Modified August 13, 2014. to place the Poposauridae outside the Archosauria. 

Lotosaurus adentus (Zhang 1975. Figure 1) Anisian, Early Triassic ~240 mya, 2.5 m in length, the only toothless sailback archosaur, has been a difficult taxon to nest because it is so unlike other archosaurs.

Nesbitt (2003) nested Lotosaurus with the other sailback archosaurs, Arizonasaurus and Ctenosauriscus, despite the obvious differences (like teeth vs. no teeth). He recovered these within the otherwise sail-less Poposauridae along with Chatterjeea (aka Shuvosaurus) and within the otherwise sail-less Rauisuchia (top Triassic predators, like Prestosuchus). The Lotosaurus skull (wider than tall and lacking teeth) was actually quite different than the rest of the rauisuchians. The hips were different too.

Later, Nesbitt (2011) nested Lotosaurus between Sillosuchus and Poposaurus, one node beyond Arizonasaurus and Xilosuchus, all within the Poposauroidea with Qianosuchus at its base. This branch nested as a sister to Rauisuchidae + Crocodylomorpha together called Loricata, a resurrected clade name from 1820 that was defined by Nesbitt as the most inclusive clade containing Crocodylus niloticus (the Nile crocodile), but not PoposaurusOrnithosuchus, or Aetosaurus. Ticinosuchus nested as basal to all these taxa in an older clade, Paracrocodylomorpha (the last common ancestor of Poposauridae and Crocodylomorpha and all of its descendants).

So the questions are:
1) What is Lotosaurus, if not a rauisuchid?
2) What is Arizonasaurus, if not a poposauroid? And
3) How does Ctenosauriscus. known only by a giant sailback fit it?

Let’s Compare the Candidates
When you compare Lotosaurus to its most parsimonious sister taxa and other sailback archosaurs (Figure 1), the affinities and shared traits become more apparent. Here Vjushkovia was basal to the rauisuchians and these included Arizonasaurus and Xilosuchus. The surprisingly long neck of Xilosuchus demonstrates affinities to another sister, Qianosuchus.

 

 

FFigure 2. Lotosaurus compared to sister taxa and other sailback archosaurs and Silesaurus.

Figure 2. Lotosaurus compared to sister taxa and other sailback archosaurs and Silesaurus.

Phylogenetic Analysis
The large reptile tree nested Lotosaurus with Silesaurus (Figure 1) and both of these within the Poposauridae outside the Archosauria. Overall similar, the ilia of both taxa were virtually identical and both had laterally oriented acetabula. The scapulae had the same shape. Both were plant-eaters, based on the leaf-like teeth of Silesaurus and the toothless jaws of Lotosaurus.

The large study nested Arizonasaurus with Yarasuchus and Qianosuchus with Ticinosuchus and aetosaurs. Arizonasaurus had a smaller pectoral girdle and longer ventral pelvis, suggesting it was a biped. The sail extended only between the pectoral girdle and tail.

By contrast, the sail extended anterior to the scapula in Lotosaurus and Ctenosauriscus. That may be the only clear clue as to the affinities of the first (to be discovered) and largest of the saibacks.

  

Figure 4. Lotosaurus family tree according to the large study, not the Nesbitt study.

Figure 4. Lotosaurus family tree according to the large study, not the Nesbitt study. Pisanosaurus is no longer a poposaurid but a basal ornithiscian. 

Let’s Compare Skulls
The skulls of candidate and sister taxa help differentiate the two sailbacks from one another. The pink band illustrates the lineage of rauisuchians from Vjushkovia to Aetosaurus, which Nesbitt (2011) found were sister to Lotosaurus. The yellow and green bands are the two clades within the Poposauridae. Unfortunately no skull is known for Poposaurus. Evidently, all poposaurids were plant eaters with shorter skulls and several were toothless.

References
Nesbitt SJ 2003. Arizonasaurus and its implications for archosaur divergence
Sterling J. Nesbitt Proceedings of the Royal Society, London B (Suppl.) 270, S234–S237. DOI 10.1098/rsbl.2003.0066
Weinbaum JC and Hungerbuhler A 2007. A Revision of Poposaurus gracilis (Archosauria: Suchia) based on two new specimens from the Late Triassic of the southwestern USA. Palaeontologische Zeitschrift 81(2):131-145.
Zhang F-K 1975. A new thecodont Lotosaurus, from Middle Triassic of Hunan. Vertebrata PalAsiatica 13:144-147.

wiki/Lotosaurus

The Truth About “Toothless” Pterosaurs

While basal pterosaurs had lots of teeth, and certain derived pterosaurs, like SoS 2179 and Pterodaustro had dozens to hundreds of teeth, certain pteroaurs appear to have been toothless – or so they say…

I’ll just cut to the chase.
Apparently “toothless” pterosaurs, like Pteranodon, Nyctosaurus and Tapejara actually had one tooth at the tip of the premaxilla and one tooth at the tip of the dentary. That’s how the tips were able to become and remain so sharp. Like the wing ungual and manual digit V, these single teeth have been overlooked by all prior pterosaur workers. The evolution of these single anteriorly-directed teetth can be documented in predecessor taxa among the germanodactylids, but it is still not clear whether one tooth became smaller or the two anterior teeth fused to become one. It seems reasonable that these teeth would be replaced with new teeth at the root, but this has not yet been documented. In the images below, if there was a “next” tooth, it is not apparent.

KUVP 66130 mandible tip

Figure 1. Click to enlarge. The tooth at the tip the mandible of KUVP 66130, a nyctosaurid.

The tooth at the tip of the rostrum of KUVP 66130

Figure 2. Click to enlarge. The tooth at the tip of the rostrum of KUVP 66130, a nyctosaurid.

In the nyctosaurids above the dentary and premaxillary tooth tips are shown.

The tooth at the tip of the rostrum of Tapejara

Figure 3. Click to enlarge. The tooth at the tip of the rostrum of Tapejara.

The Evolution of “Toothless” Pterosaurs
In several pterosaurs the medial or first premaxillary tooth was procumbent. It angled forward as well as downward. In B St 1967 I 276 (No. 6 of Wellnhofer 1970), the tiniest pterosaur, the anterior premaxillary tooth was procumbent.

Figure 4. The rostrum of No. 6 in which the teeth at the tip were procumbent, but not anteriorly oriented.

In the specimen from the Senckenberg-Museum Frankfurt a. M. No. 4072, (No. 12 of Wellnhofer 1970) the anterior tooth was oriented further anteriorly and may have been a single tooth.

No. 12 rostrum

Figure 5. The jaw tips of No. 12

In Germanodactylus the SMNK-PAL 6592 specimen, the anterior premaxillary and dentary teeth were fully anterior in orientation.

Germanodactylus skull

Figure 6. Germanodactylus skull with anteriorly-oriented jaw tips

Germanodactylus skull drawing

Figure 7. Germanodactylus SMNK skull drawing showing anteriorly-oriented teeth at jaw tips.

You’ll find anteriorly oriented teeth in all germanodactylids and their sharp-snouted descendants including dsungaripeterids, shenzhoupterids, tapejarids, nyctosaurids, eopteranodontids and pteranodontids. I have not been able to closely examine the anterior jaws of azhdarchids, but photographic examination appears to show tiny (< 1 mm) teeth lining the jaws of Quetzalcoatlus sp.

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.