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 5. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020.

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

Figure 4. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

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

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