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.

How did Moschops take a drink of water?

The dinocephalian synapsid,
Moschops (Fig. 1), looks like it could not bend its neck down to take a drink of water from the shoreline, giraffe-style.

Figure 1. Stiff-necked Moschops did not need to lean down, giraffe-style, to drink water. It could just wade into chin deep water.

Figure 1. Stiff-necked Moschops did not need to lean down, giraffe-style, to drink water. It could just wade into chin deep water.

But Moschops could wade
into chin-deep water, maybe where it’s plant diet sprouted. Okay, no big deal, but I’ve wondered this and the simplest answer did not come to me for some time, probably because I was giraffe- and wildebeest-biased. Watching my dog walk knee deep into a pond cleared the air for me.

Biseridens and Phthinosuchus – two misunderstood therapsids

Biseridens, according to Wikipedia,
“is the most basal genus of anomodont therapsid.”

Not so,
according to the large reptile tree (Fig. 3), which nests Biseridens (Fig. 1, Li and Cheng 1997; Liu, Rubidge and Li 2009) far from anomodonts, between Archaeosyoson and Jonkeria and kin among the Tapinocephalia.

Figure 1. Biseridens and Phthinosuchus, two related therapsids that have been giving paleontologists fits.

Figure 1. Biseridens and Phthinosuchus, two related therapsids that have been giving paleontologists fits.

Phthinosuchus, according to Wikipedia
“is the sole member of the the family Phthinosuchidae. It may have been one of the most primitive therapsids.” Not so, according to the large reptile tree (Fig. 2) where Phthinosuchus (Fig. 1, Efremov 1954) nests between Eotitanosuchus and ArchaeosyodonBiseridens at the base of the Dinocephalia.

So traditional nestings seem to be a little behind the times.
According to Liu, Rubidge and Li 2009, “Synapomorphies that distinguish Biseridens as an anomodont and not an eotitanosuchian as previously described: short snout (1); dorsally elevated zygomatic arch (2) and septomaxilla lacking elongated posterodorsal process between nasal and maxilla (3). The presence of a differentiated tooth row (4); denticles on vomer, palatine and pterygoid (5); contact between tabular and opisthotic (6); lateral process of transverse flange of pterygoid free of posterior ramus and absence of mandibular foramen exclude it from other anomodonts (7). Cladistic analysis indicates Biseridens to be the most basal anomodont (8).

Well, according to the large reptile tree…

  1. Eotitanosuchus has a long snout because it is basal to the clade of long snouted basal gorgonopsians and therocephalians. Biseridens ancestors, like Phthinosuchus, and Archaeosyodon, never had a long snout.
  2. the zygomatic arch (squamosal principally) is not dorsally elevated in the fossil (Fig. 1)
  3. sisters likewise lack this septomaxilla trait
  4. the dual rows of post-canine teeth and the large orbit in Biseridens are autapomorphies that distinguish it from sisters
  5. Denticlaes are also found on the palate of Phthinosuchus. I don’t have data for closer sisters.
  6. I don’t have comparable occipital data here
  7. I don’t have comparable palatal data here
  8. Be careful when a taxon nests as the ‘most basal’ to any clade without many more basal taxa on the inclusion list. As in another purported basal synapsid taxon, Caseasauria, it turns out that Biseridens actually nests elsewhere (Fig. 2).

Learn more about basal anomodonts here.

Figure 3. Basal therapsid tree.

Figure 2. Basal therapsid tree. Note the nestings of Phthinosuchus and Biseridens far from where tradition al paleontologists have been saying. I think more taxa near the base of the tree make tis tree distinct. Note the weak bootstrap scores at the nodes splitting Suminia from Venjukovia and splitting the basal dromasaurs.

 

References
Efremov IA 1954, The fauna of terrestrial vertebrates in the Permian copper sandstones of wester Cis-Urals: Travaux de I’institut Paleozoologique de l’Academie des Sciences de l’URSS, v. 54, 416pp.
Li J and Cheng Z 1997. First discovery of eotitanosuchian (Therapsida, Synapsida) of China. Vertebr. Palasiatica 35, 268–282.
Liu J, Rubidge B and Li J 2009. A new specimen of Biseridens qilianicus indicates its phylogenetic position as the most basal anomodont. Proceedings of the Royal Society B 277 (1679): 285–292. online

wiki/Biseridens
wiki/Jonkeria
wiki/Phthinosuchus

 

Estemmenosuchus skull sutures

The data I have
for Estemmenosuchus comes from a well-lit by low resolution image complete with halftone dots and moire patterns (Fig. 1). Nevertheless, I think I can find sutures on the image.

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

Figure1. The skull sutures on Esttemmenosuchus mirabilis (PIN 1758/6). When you score a skull for analysis, you have to have this data. I think that’s the right cheekbone peeking through the naris. See how colors make this interpretation clear, whether accurate or not? The ascending process of the premaxilla look like it spreads laterally. Think of that as an option. That’s the squamosal forming the tip of the cheek horn. Yes, you can still see the moire pattern formed by the halftone dots.

Estemmenosuchus uralensis (Middle Permian, Tchudinov 1960, 1968; Holotype PIN 1758/4 Skull length: 60 cm;  E. mirabilis PIN 1758/6) could be an omnivore. Considering its bulk and short thick legs, it is more likely an herbivore, like a hippo.

Estemmenosuchus skin
According to Wikipedia, “The fossil material includes an exceptionally well preserved skin impression. The skin appears to be smooth and undifferentiated with no signs of either hairs or scales but with evidence of being well supplied with glands.”

Estemmenosuchus cover

Figure 3. Estemmenosuchus cover

So I made a big mistake
back in 1991 when I illustrated Estemmenosuchus with scales on the cover of this book. The longer you linger the more you learn.

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.

A Few Days with Stenocybus

The genus Stenocybus (Cheng and Li 1997)  is known from a complete skull and a few bits and pieces of the skull of a second individual. Originally considered a basal dinocephalian (therapsid), a later report by Kammerer (2010) considered it a juvenile Sinophoneus, an anteosaur. Over the next few days we’ll be examining Stenocybus from several angles. It is a difficult fossil to deal with (working from photos alone) and I made a few mistakes on my earlier attempt (nothing earth-shattering) that I will attempt to rectify. I’ve had experience working on that troublesome and largely disarticulated palate lately, so there will be new things to talk about. Suggestions and corrections will be welcome!

The traditional reconstruction of Stenocybus.

Figure 1. The traditional and original reconstruction of Stenocybus.

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
Cheng Z and Li J 1997. A new genus of primitive dinocephalian – the third report on Late Permian Dashankou lower tetrapod fauna. Vertebrata PalAsiatica 35 (1): 35-43. [in Chinese with English summary]
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia), Journal of Systematic Palaeontology, 9: 2, 261 — 304, First published on: 13 December 2010 (iFirst)

wiki/Stenocybus