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).

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.

Figure x. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

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 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

 

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.

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.

Updated January 11, 2020
with better data in Spindler 2020.

Updated June 14, 2021
with a new tracing of Martensius, a new sister for Tetraceratops.

In a nutshell: 
Better data helped to re-identify the jumble of bones in the posterior skull and palate.

Figure 1. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020.

Figure 2. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

As reported earlier,
Tetraceratops is still a sister to the limnoscelids,  Tetraceratops is not a basal therapsid/synapsid, as reported earlier by referenced authors (see below, none of whom tested with limnoscelids). In the large reptile tree it nest with the above (Fig. 2) taxa. 

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 limnoscelids, 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