The big and small Estemmenosuchus (Dinocephalia, Therapsida, Synapsida, Archosauromorpha)

Figure 1. There are two known Estemmenosuchus species, the smaller famous one, E. mirabilis, and the larger less famous one, E. uralensis, here shown to scale. The ectopterygoid (Tr here) is oddly placed, posterior to the pterygoid, but of the standard shape, if I'm reading this drawing correctly.

Figure 1. There are two known Estemmenosuchus species, the smaller famous one, E. mirabilis, and the larger less famous one, E. uralensis, here shown to scale. The ectopterygoid (Tr here) is oddly placed in E. uralensis, posterior to the pterygoid, but of the standard shape, if I’m reading this drawing correctly. the palatine/pterygoid pads are part of the herbivorous chewing apparatus.

Earlier we looked at
the baroque skull of Estemmenosuchus (late Permian, Tchudinov 1960, 1968) here, here and here. Today they are shown together to scale, with one about twice the size of the other. E. mirabilis is the more famous one because it is the more bizarre one, yet it is smaller than E. uralenesis. Both the postfrontals and the jugals expand distally to proceed these skull ‘horns’. A smaller one is produced by the premaxillary ascending process. And other smaller bumps are produced by the postorbital and frontal.

Looking at the palate drawings
we see a row of palatine teeth, a pterygoid with a row of teeth on the transverse process and more on the medial process, and some oddly placed ectopterygoids posterior to the pterygoids.

Figure1. The skull sutures on Esttemmenosuchus mirabilis. When you score a skull for analysis, you have to have this data.

Figure3. The skull of Estemmenosuchus mirabilis, the hippopotamus of the Late Permian. Note the large procumbent teeth.

The maxilla has
two parallel rows of post canine teeth in E. mirabilis, essentially one row of marginal maxillary teeth in E. uralensis. But the maxillary/palatine row in E. uralensis is a new twist on the same construction. We’ve seen multiple rows of maxillary teeth in the taxa that lead up to rhynchosaur lepidosaurs.

References
Tchudinov PK 1960. Diagnosen der Therapsida des oberen Perm von Ezhovo: Paleontologischeskii Zhural, 1960, n. 4, p. 81-94.
Tchudinov PK 1968. Structure of the integuments of theriomorphs. Doklady Acad. Nauk SSSR. 179:207-210.

Atopodentatus: fixing a mistake and Science marches on

Two years ago, when
Atopodentatus unicus was first described (Cheng et al. 2014) it (WIGM SPC V1107) was thought to have an odd downturned rostrum with medially facing premaxillae. That very odd (autapomorphic) interpretation was widely accepted.

Recently
Chun et al. 2016 found more fossils (IVPP V20291, IVPP V20292) that showed the crushing had introduced an illusion in the first Atopodentatus. The jaws were actually wide and flat, not deep (Fig. 2).

Figure 1. DGS tracings of the second and third specimens of Atopodentatus in several views.

Figure 1. DGS tracings of the second and third specimens of Atopodentatus in several views. Note the foramina in the nasals, a likely location for the salt gland. The mandibles were both rotated axially so that the glenoid/jaw joint was found on the former medial surface.

Chun et al. 2016 reported,
“The evidence indicates a novel feeding mechanism wherein the chisel-shaped teeth were used to scrape algae off the substrate, and the plant matter that was loosened was filtered from the water column through the more posteriorly positioned tooth mesh. This is the oldest record of herbivory within marine reptiles.”

Maybe — maybe not.
To me those pmx teeth look like mud/sand rakes/sievers. And IF so, Atopodentatus was seeking burrowing organisms that could be filtered by the posterior jaws. But on the other hand, we have a living analog…

Like a modern marine iguana?
This YouTube video shows a marine iguana grazing on algae coating the underwater rocks surrounding the Galapagos. Note the narrow-snouted iguana twists its head and uses its cheek teeth on the flat part of its face to nip the plants off the rocks. The video describes those teeth as ‘razor sharp’, but they are not. They are tricuspid, acting like rakes. In a way the duplicate having three times as many single-cusp teeth.

Figure x. Marine iguana teeth are tricuspid.

Figure x. Marine iguana teeth are tricuspid

Unfortunately
neither Cheng et al. nor Chun et al were able to decide what sort of marine reptile Atopodentatus was. Here, in the large reptile tree, even with the new changes to the skull, Atopodentatus nests outside the Sauropterygidae, as a marine younginiform, more derived than Claudiosaurus, nesting with the turtle-like Sinosaurosphargis and the longer but still wide, Largocephalosaurus (Fig. 2). Reconstructions help.

Figure 2. Atopodentatus nests with two other pre-sauropterygian marine younginforms, Sinosaurosphargis and Largocephalosaurus.

Figure 2. Atopodentatus nests with two other pre-sauropterygian marine younginforms, Sinosaurosphargis and Largocephalosaurus. Note the narrower postorbital skull compared to these sisters.

These three were bottom feeders. 
All were from the Middle Triassic. Onlly Atopodentatus had a vertical quadrate. Only Atopdentatus had a hole in its skull, presumably for a salt gland.

Some bones missed by Chun et al. 2016 include:

  1. supratemporals
  2. postparietals
  3. tabulars
  4. quadratojugals
  5. and the large lacrimals.
Figure 3. The two IVPP specimens of Atopodentatus both show the wide premaxillae ideals for scraping and raking. The pterygoids had a shagreen of tiny teeth. The maxillae also have filtering needle-like teeth. Note the presence of the lacrimal and supratemporal missed by first hand observation.

Figure 3. The two IVPP specimens of Atopodentatus both show the wide premaxillae ideals for scraping and raking. The pterygoids had a shagreen of tiny teeth. The maxillae also have filtering needle-like teeth. Note the presence of the lacrimal and supratemporal missed by first hand observation. Is that a salt gland location posterior to the nasals?

Was this a blunder? Or an honest mistake?
Let’s be professional about this and call it an honest mistake. And notice there is no reason to be embarrassed by such mistakes. We fix them and move on. Take these examples:

  1. Elasmosaurus had the head on the wrong end originally.
  2. Yi qi was thought to have an extra long wrist bone that turned out to be a displaced ulna on one side, a radius on the other side.
  3. Sordes was thought to have deep chord wings and a uropatagium between the legs, not including the tail.
  4. Longisquama was thought to have short hind limbs.
  5. The nesting of Vancleavea with archosauriformes.
  6. Or pterosaurs with dinosaurs and Scleromochlus.
  7. The wrong skull and dragging tail for Brontosaurus.
  8. … and all the little boo-boos that creep into everyone’s matrices (including yours truly)

Note that
one author on the original paper (Cheng L) is also an author on the new paper. Here’s how the new set of authors handled the prior mistake from the abstract, “The skull displays a pronounced hammerhead shape that was hitherto unknown.”

And from the text:
“Atopodentatus unicus was originally described as a putative sauropterygian filter feeder with a downturned rostrum, supposedly used to stir up invertebrates in soft sediment in a flamingo-like manner. Here, we describe two new specimens… that require a very different interpretation of skull morphology and provide evidence for an even more remarkable feeding strategy. The new specimens clearly demonstrate that rather than being downturned, the rostrum was developed into a “hammerhead” with pronounced lateral processes formed by the premaxillae and maxillae in the upper jaw and mirrored by the dentary in the lower jaw.”

That’s a nice way to do it. Don’t you agree?
We can all take a lesson from this.

While we’re on the subject of filter feeding marine reptiles…
Let’s not forget the oddly toothed thallattosaur, Helveticosaurus (Fig. 4, Middle Triassic). Helveticosaurus had such long cheek teeth they could not have been used for chewing or stabbing. Instead they look like baleen strainers. Helveticosaurus had long fangs anteriorly, perhaps useful for scraping rather than stabbing.

Figure 4. Helveticosaurus had cheek teeth that look like baleen strainers and long fangs anteriorly.

Figure 4. Helveticosaurus had cheek teeth that look like baleen strainers and long fangs anteriorly.

The proximal outgroup taxon for Atopodentatus
is the Late Permian marine younginiform, Adelosaurus, which doesn’t have any obvious marine traits. The skull is also unknown. And the phylogenetic difference between the Late Permian and Middle Triassic taxa are obvious (Fig. 5).

Figure 5. Atopodentatus compared to more primitive sister taxa, Adelosaurus and Claudiosaurus.

Figure 5. Atopodentatus compared to more primitive sister taxa, Adelosaurus and Claudiosaurus to scale.

References
Cheng L, Chen XH, Shang QH and Wu XC 2014. A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Naturwissenschaften. doi:10.1007/s00114-014-1148-4.
Chun L, Rieppel O, Cheng L and Fraser NC 2016. The earliest herbivorous marine reptile and its remarkable jaw apparatus. Science Advances 06 May 2016: 2(5), e1501659
DOI: 10.1126/sciadv.1501659

 

 

 

Patterns of Herbivory within the Reptilia

I recently mapped the herbivorous reptiles on the large reptile tree. Click here to see it. Some interesting patterns emerged.

The separation between plant-eaters and insect-eaters formed the basal split in the large reptile tree. The emergence of Limnoscelis and its kin and Lanthanosuchus and its kin from this clade bears further scrutiny. I’m sure there’s a story brewing there. Turtles also emerged from this clade of herbivores. Among charted lepidosauromorphs we don’t see any other herbivores until Iguana and even it supplments with insects when young. Let me know if I’m missing any others.

On the archosauromorph side, Edaphosaurus is the first herbivore with several therapsid clades not far behind. Thereafter we don’t see any until the Placodontia (if they were indeed herbivores and not shell crushers), the Aetosaurs and the Phytodinosauria.

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
Diedrich CG 2011. Fossil middle triassic “sea cows” – placodont reptiles as macroalgae feeders along the north-western tethys coastline with pangaea and in the germanic basin. Natural Science 3 (1) 9-27 (2011)


Acerosodontosaurus – a Key Taxon at the Base of the Diapsida

The “Big Belly” Basal Diapsid
Acerosodontosaurus (Currie 1980, Bickelmann, Müller and Reisz 2009) Late Permian, was the fat kid on the block (=clade). Even so, this largely ignored and otherwise unspectacular taxon is key to our understanding of all higher diapsids, both marine and terrestrial. Hard to believe a sister to Acerosodontosaurus was ancestral to both hummingbirds and elasmosaurs, for instance. That’s the beauty of reptile evolution.

Acerosodontosaurus

Figure 1. Acerosodontosaurus in lateral view with a closeup of the hand and a cross section of the rib cage. This was the most robust member of the basal Diapsida. It had the largest dorsal vertebrae and deepest rib cage among its sisters. Such characters typically indicate an herbivorous diet, distinct from all sister taxa.

Acerosodontosaurus piveteaui was originally considered a younginiform. A later analysis by Bickelmann et al. (2009) nested Acerosodontosaurus with Hovasaurus and the same sisters recovered in the large reptile family tree seen here (Fig. 2). Always good to report when phylogenetic testing supports the literature.

The Questionable Quadratojugal/Rib Fragment
Bickelmann, Müller and Reisz (2009) determined that a bone considered to be quadratojugal (Fig. 1 in red) was instead a portion of a rib. Because of that new identification the authors considered Acerosodontosaurus a phylogenetic enigma in which the phylogenetic position was poorly understood, so they retested it. Bickelmann, Müller and Reisz (2009) then nested Acerosodontosaurus with Hovasaurus.

Ironically that questionable “rib fragment” fit perfectly into a reconstruction as a quadratojugal – BUT – the quadratojugal was the first bone to disappear in sister taxa – AND – the quadratojugal was considered missing in both Hovasaurus and Claudiosaurus, (which is disputed here). In any case and either way, one error in coding doesn’t change things much in a study of this size. Phylogenetically it just doesn’t matter. It just shifts the disappearance of the quadratojugal up or down the line.

Supporting the hypothesis that the quadratojugal was still present in Acerosodontosaurus and Claudiosaurus is the fact that successor taxa, including Stereosternum, Mesosaurus and ichthyosauriformes like Hupesuchus and Utatsusaurus all have a quadratojugal. Moreover, there are no other genuine rib fragments anywhere near the skull.

Basal diapsids.

Figure 2. Basal diapsids. Basal terrestrial forms in white. Younginiforms in green. Enaliosauria in blue. Mesosauria + Thalattosauria + Ichthyosauriformes in deeper blue.

Phylogenetic Nesting
Here Acerosodontosaurus nested at the base of two major clades, the marine Enaliosauria (= (Mesosauria + (Ichthyosauriformes + Thalattosauriformes)) + Sauropterygia) and the terrestrial Younginiformes, here represented by Thadeosaurus. So it’s a key taxon that should be used as an outgroup in focused studies of both clades.

Diet
In Acerosodontosaurus the large size of the dorsal vertebrae, coupled with the deep and wide dorsal ribs, coupled with the short robust limbs and lack of a canine tooth all point toward an herbivorous diet. No succeeding taxa had a canine tooth, but no succeeding taxon had the hallmark “big belly” of this possible herbivore. Alternatively, Acerosodontosaurus may have fed on small invertebrates and other slow-moving prey.

Niche
Acerosodontosaurus was considered aquatic in niche, like its sister taxa, the deep-tailed Hovasaurus and the less deep-tailed Thadeosaurus. The descendants of the former became increasingly marine. Descendants of the latter became increasingly terrestrial.

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
Currie PJ 1980. A new younginid (Reptilia: Eosuchia) from the Upper Permian of Madagascar. Canadian Journal of Earth Sciences 17(4):500-51.
Bickelmann C, Müller J and Reisz RR 2009. The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of “younginiform” reptiles. Canadian Journal of Earth Sciences 46:651-661.

wiki/Acerosodontosaurus

Revueltosaurus Keeps Bouncing Around

Updated December 09, 2014 as Revueltosaurus now nests with Fugusuchus.

Revueltosaurus has revealed itself to us (and to me) a little bit at a time (see below). That is okay. It’s still good science. Best guesses based on limited data are just fine. Better guesses based on more data are better, of course. This doesn’t always happen (see the flap on pterosaur origins), but at least here, now based on virtually complete skeletal material, that little Triassic oddball, Revueltosaurus, may soon stop bouncing around the reptile family tree. It’s a fun and interesting story.

First, Just Teeth – a Basal Ornithischian
When Hunt (1989) first described Revueltosaurus, it was a Triassic dinosaur, based on its teeth alone, which resembled those of basal ornithischians.

Then, Some Crushed Skull Parts, a Pelvis and Scapula – a Pseudosuchian
Parker et al. (2005) redescribed Revueltosaurus as a pseudosuchian based on some skull, pectoral and pelvic bones. Unfortunately they could not place it within any known monophyletic clade.

Reconstruction of Revueltosaurus from Parker et al. 2005.

Figure 1. Reconstruction of Revueltosaurus from Parker et al. 2005.

Third, A Nesbitt Skull Reconstruction – a Basal Aetosaur
Recently Nesbitt (2011) nested Revueltosaurus at the base of the Aetosauria as a sister to Turfanosuchus, Gracilisuchus and Ticinosuchus — all taxa just ouside of the Archosauria. Here, Ticinosuchus is at the base of the aetosauria.

Skull reconstruction of Revueltosaurus traced from Nesbitt 2011.

Figure 2. Skull reconstruction of Revueltosaurus traced from Nesbitt 2011.

Finally, an Overall Reconstruction by Jeffrey Martz – a Fugusuchus Sister
A recent award-winning reconstruction by Jeffrey Martz illustrated the complete skeleton and osteoderm covering of Revueltosaurus. Captions along with this illustration indicate that an aetosaur sisterhood is still favored. Although the skull was very close to the reconstruction offered by Nesbitt, it was distinct enough to cause a phylogenetic shift to a sister to Fugusuchus, a basal erythrosuchid.

Revueltosaurus revised from a tracing by Jeffrey Martz.

Figure 4. Revueltosaurus revised from a tracing by Jeffrey Martz. The limbs and tail have been straightened just a bit.

Is Revueltosaurus a Mini-Fugusuchus?
Not quite. Likely they shared a common ancestor. The teeth of Revueltosaurus indicate a diet of plants, but the small rib cage and the reduced depth of the pubis do not support an herbivorous diet. The shorter hind limbs of Revueltosaurus indicate that it was a full-time quadruped.

Figure 1. Revueltosaurus compared to its big sister, Fugusuchus, a basal erythrosuchid.

Figure 1. Revueltosaurus compared to its big sister, Fugusuchus, a basal erythrosuchid.

The Question Is
What is real?

References
Hunt AP 1989. A new ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. In Lucas, S. G. and A. P. Hunt (Eds.), Dawn of the age of dinosaurs in the American Southwest 355–358.
Parker WG., et al. 2005. The Pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. In Proceedings of the Royal Society London B 272(1566):963–969.

wiki/Revueltosaurus