The origin of Limnoscelis

Limnoscelis, according to Wikipedia, “is a genus of large (1.5 m in total length), very reptile-like diadectomorph (a type of reptile-like amphibian) from the Early Permian of North America. Contrary to other diadectomorphans, Limnoscelis appear to have been a carnivore. Though the post cranial skeleton is very similar to the early large bodied reptiles like pelycosaurs and pareiasaurs, the digits lacked claws, and the bones of the ankle bones were fused like in other reptile-like amphibians. This would not allow them to use their feet actively in traction, but rather as holdfasts, indicating Limnoscelis primarily hunted slow moving prey.”

Figure 1. Limnoscelis and two suitable ancestral taxa, Orobates and Milleretta, all shown to scale (below) and to fit (above).

Figure 1. Limnoscelis and two suitable ancestral taxa, Orobates and Milleretta, all shown to scale (below) and to fit (above).

The large reptile tree nested Limnoscelis well within the Lepidosauromorpha branch of the Reptilia/Amniota along with the smaller Orobates and not far from tiny Milleretta (Fig. 1). The latter two are the most suitable ancestral morphologies yet found on the large reptile tree.

Limnoscelis and Orobates do not nest with Diadectes and other diadectomorphs, but also, not too far away from that clade. The Limnoscelis clade still nests with Tseajiaia and Tetraceratops.

Are those carnivorous teeth in Limnoscelis?
Most sister taxa in surrounding clades are likely herbivores. Some related taxa had canines, but not Limnoscelis.

When are we going find consensus
on the nesting of Limnoscelis? We need a competing large gamut phylogenetic analysis to confirm or refute the topology recovered by the large reptile tree. Either that, or let the results of the large reptile tree get published.

Added Janurary 10, 2019
Saurorictus (Fig. 2; Late Permian; Modesto and Smith 2001; SAM PK-8666), nesting at the base of the captorhinids and their sisters, is the proximal outgroup taxon in the LRT now. Except for size, the resemblance is striking.

Figure 1. Limnoscelis and its outgroup sister, Saurorictus.

Figure 2. Limnoscelis and its outgroup sister, Saurorictus.

References
Berman DS, Reisz RR and Scott D 2010. Redescription of the skull of Limnoscelis paludis Williston (Diadectomorpha: Limnoscelidae) from the Pennsylvanian of Canon del Cobre, northern New Mexico: In: Carboniferous-Permian Transition in Canon del Cobre, Northern New Mexico, edited by Lucas, S. G., Schneider, J. W., and Spielmann, New Mexico Museum of Natural History & Science, Bulletin 49, p. 185-210.
Modesto SP and Smith RMH 2001. A new Late Permian captorhinid reptile: a first record from the South African Karoo. Journal of Vertebrate Paleontology 21(3): 405–409.
Romer AS 1946. The primitive reptile Limnoscelis restudied American Journal of Science, Vol. 244:149-188
Williston SW 1911. A new family of reptiles from the Permian of New Mexico: American Journal of Science, Series 4, 31:378-398.

wiki/Saurorictus
wiki/Limnoscelis

 

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The deep mandible of Tseajaia

The original reconstruction of Tseajaia (Vaughn 1964, Moss 1972) has a problem (Fig. 1). The mandible is too deep to fit inside the jaws. But, no worries! It’s a quick fix.

Figure 1. The original reconstruction of the Tseajaia skull and closed mandibles did not take into account the great depth of the anterior mandible. That is remedied here.

Figure 1. The original reconstruction of the Tseajaia skull and closed mandibles did not take into account the great depth of the anterior mandible. That is remedied here.

References
Vaughn PP 1964. Vertebrates from the Organ Rock Shale of the Cutler Group, Permian of Monument Valley and Vicinity, Utah and Arizona: Journal of Paleontology 38:567-583.
Moss JL 1972. The Morphology and phylogenetic relationship of the Lower Permian tetrapodTseajaia campi Vaughn (Amphibia: Seymouriamorpha): University of California Publications in Geological Sciences 98:1-72.

wiki/Tseajaia

Revisiting Tetraceratops: a bone misidentified.

In a nutshell: 
What we thought was the postorbital and ascending process of the juggl in Tetraceratops is actually the quadratojugal and posterior process of the jugal, rotated 90 degrees in the same taphonomic event that moved the rest of the posterior skull elements.

New reconstruction of the limnoscelid Tetraceratops.

Figure 1. New reconstruction of the limnoscelid Tetraceratops.

This is why the left and right postorbitals did not match in the Amson and Laurin (2011) interpretation, which I earlier bought into. Now it appears the left postorbital is really a quadratojugal. So now Tetraceratops does not stand out as such an oddball.

Color tracing of Tetraceratops. note the quadratojugal (orange) and posterior jugal (blue) have been rotated into the position formerly occupied by the postorbital.

Figure 2. Color tracing of Tetraceratops. note the quadratojugal (orange) and posterior jugal (blue) have been rotated into the position formerly occupied by the postorbital. The short ascending process of the jugal is broken off and sitting atop the quadratojugal.

The squamosal (in pink) is there, largely in the orbit, busted up into several cracked pieces, like a crushed eggshell.

The parietal (butter yellow) is likewise busted up. It was a rough burial. Not all the pieces are visible.

What was originally thought to represent a large lateral temporal fenestra turns out to be a rotated postfrontal (light orange) / postorbital (brown) / supratemporal (indigo) showing part of its interior (brain case).

Now the reconstruction produces both a skull and an orbit that are not taller than wide.

Otherwise, very few obvious other changes. The colors on the image tell the rest of the story. The frontals and most of the parietals remain unidentified and unfound.

As reported earlier,
Tetraceratops is still a sister to the limnoscelid, Tseajaia, and now the reconstruction has a lower skull height and rounder orbit, like that of Tseajaia and Limnoscelis. Tetraceratops is not a basal therapsid/synapsid, as reported earlier by referenced authors (see below, none of whom tested with Tseajaia). In the large reptile tree it nest with the above named genera. 

An additional note
The Amson and Laurin (2011) reconstruction (with large lateral temporal fenestrae) was also tested as if it were a valid taxon. And it, too, nested with Tseajaia, even with a large lateral temporal fenestra. So the nesting is robust.

We looked at Tetraceratops earlier here and here.

References
Amson E and Laurin M 2011. On the affinities of Tetraceratops insignis, an Early Permian synapsid. Acta Palaeontologica Polonica 56(2):301-312. online pdf
Conrad J and Sidor CA 2001. Re−evaluation of Tetraceratops insignis (Synapsida: Sphenacodontia). Journal of Vertebrate Paleontology 21: 42A.
Laurin M and Reisz RR. 1996. The osteology and relationships of Tetraceratops insignis, the oldest known therapsid. Journal of Vertebrate Paleontology 16:95-102. doi:10.1080/02724634.1996.10011287.
Matthew WD 1908. A four-horned pelycosaurian from the Permian of Texas. Bulletin of the American Museum of Natural History 24:183-185.
Sidor CA and Hopson JA 1998. “Ghost lineages and “mammalness”: Assessing the temporal pattern of character acquisition in the Synapsida”. Paleobiology 24: 254–273.

wiki/Tetraceratops