A few loose ends
from the large reptile tree (LRT) that I failed to mention earlier:
Saurorictus (Fig. 1; Late Permian; Modesto and Smith 2001; SAM PK-8666), nesting at the base of the captorhinids and their basal lepidosauromorph sisters, is the proximal outgroup taxon in the LRT for Limnoscelis. Except for size, the resemblance is striking and, so far, unreported in traditional paleontology.
Wikipedia still thinks of Limnoscelis as a “reptile-like diadectomorph (a type of reptile-like amphibian).” Romer 1946 and Willistion 1911 pegged it as a reptile.
While we’re on the subject of the Limnoscelidae
the 2011 nesting of Tetraceratops (Fig. 2) with Tseajaia and Limnoscelis in the LRT has not been challenged. Relying on taxon exclusion, Tetraceratops was nested as a basal therapsid most recently by Amson and Laurin 2011 and earlier by other studies that excluded other clades. The thin squamosal broken into smaller pieces that drifted into the orbit were overlooked and ignored by earlier studies. The convergence is interesting, though. Spindler 2014 did question the nesting of Tetraceratops as a basal therapsid, but only on the basis of a trait list, not by expanding their taxon list to Tseajaia and its sisters.
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: Pp. 185-210 in: Carboniferous-Permian Transition in Canon del Cobre, Northern New Mexico, edited by Lucas, Schneider and Spielmann, New Mexico Museum of Natural History & Science, Bulletin 49.
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.
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.
Matthew WD 1908. A four-horned pelycosaurian from the Permian of Texas.
Bulletin of the American Museum of Natural History 24:183-185.
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.\
Sidor CA and Hopson JA 1998. “Ghost lineages and “mammalness”: Assessing the temporal pattern of character acquisition in the Synapsida”. Paleobiology 24: 254–273.
Spindler F 2014. Reviewing the question of the oldest therapsid. Paläontologie, Stratigraphie, Fazies (22) Freiberger Forschungshefte C 548: 1–7.