What is Apsisaurus?

Today’s blog will focus on Apsisaurus witteri (Laurin 1991, Fig. 1), a small Early Permian reptile of questionable affinity. The skull is incomplete. The post-crania is difficult to reassemble with available data. It needs to be seen from several views.

Apsisaurus

Figure 1. Apsisaurus witteri

Reisz, Laurin and Marjanovic (2010) in their report on Apsisaurus stated, “Paleozoic varanopid synapsids and diapsids, rare members of the terrestrial fossil assemblages, are not closely related to each other but appear to have acquired a number of interesting similarities that have resulted in their frequent misidentification.” These workers would benefit from a larger study. Here basal members of the varanopid synapsids and the protodiapsids ARE related to each other. The second evolved from the first.

Reisz, Laurin and Marjanovic (2010) also stated, Archaeovenator, based on a single small skeleton from the Upper Carboniferous of Kansas, was first identified as a diapsid reptile, but a restudy of the material clearly showed that it was a basal varanopid (Reisz and Dilkes, 2003). Perhaps the most striking examples are those of Mesenosaurus and Heleosaurus, two Middle Permian varanopid synapsids from Russia and South Africa that were previously misidentified as archosauromorph and eosuchian diapsids, respectively (Reisz and Berman, 2001; Reisz and Modesto, 2007).” Here Mesenosaurus and Heleosaurus are two basal protodiapsids outside of the clade of varanopid synapsids, but descended from them. Due to their limited gamut of taxa, Reisz, Laurin and Marjanovic (2010) were not aware of the protodiapsid grade arising from the varanopids.

Traditional Confusion Based on a Reduced Inclusion Set
A larger taxon list sheds light on earlier confusion. These new heretical nestings expose and illustrate the origin of the proto-diapsid taxon list, which was overlooked or ignored in traditional studies. Here Apsisaurus nested at the base of the non-varanopid synapsids, more primitive than Archaeothyris, the oldest known synapsid. So, Apsisaurus was not far from the base of the varanopids and not far from the protodiapsids. No wonder it was difficult to nest. More data in the future could move the lines of division.

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
Laurin M 1991. The osteology of a Lower permian eosuchian from Texas and a review of diapsid phylogeny. Zoological Journal of the Linnean Society 101 (1): 59–95. doi:10.1111/j.1096-3642.1991.tb00886.x.
Reisz RR,  Laurin M and Marjanovic D 2010. Apsisaurus witteri from the Lower Permian of Texas: yet another small varanopid synapsid, not a diapsid. Journal of Vertebrate Paleontology 30 (5): 1628–1631. doi:10.1080/02724634.2010.501441.

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