Mycterosaurus and Nikkasaurus

Mycterosaurus longiceps (Middle Permian, Williston 1915, Berman and Reisz 1982, FMNH UC692) nested with Heleosaurus as the most basal protodiapsid. Botha-Brink and Modesto (2009) nested it withMesenosaurus and Heleosaurus. The tip of the snout is unknown, but probably straight as in Heleosaurus. Berman and Reisz 1982 considered the AMNH 7002 specimen (above) another Mycterosaurus, but it has recurved canines more like those of Mesenosaurus, the maxilla is lower and the jugal had a different shape.

Nikkasaurus tatarinovi (Ivahnenko 2000) Middle Permian was a tiny basal prodiapsid with a large orbit. It retained a large quadratojugal. The fossil is missing the squamosal. It has small sharp teeth. Derived from a sister to Protorothyris, Nikkasaurus is a sister to Mycterosaurus, they both share a large orbit and fairly long snout. What appears to be a retroarticular process may be something else.

Berman DS and Reisz RR 1982. Restudy of Mycterosaurus longiceps (Reptilia, Pelycosauria) from the Lower Permian of Texas. Annals of Carnegie Museum 51, 423–453.

Botha-Brink J and Modesto SP 2009. Anatomy and Relationships of the Middle Permian Varanopid Heleosaurus scholtzi Based on a Social Aggregation from the Karoo Basin of South Africa. Journal of Vertebrate Paleontology 29(2):389-400.

Ivahnenko MF 2000. Cranial morphology and evolution of Permian Dinomorpha (Eotherapsida) of eastern Europe. Paleontological Journal 42(9):859-995. DOI: 10.1134/S0031030108090013

Broom R 1907. On some new fossil reptiles from the Karroo beds of Victoria West, South Africa. Transactions of the South African Philosophical Society 18:31–42. .

Willistion SW 1915. A New Genus and Species of American Theromorpha: Mycterosaurus longiceps. The Journal of Geology 23(6):554-559.

wiki/Mycterosaurus
wiki/Nikkasaurus

Protodiapsida

Heleosaurus

Mycterosaurus

Mesenosaurus

Archaeovenator

Broomia

Erpetonyx

Milleropsis

Diapsida

Petrolacosaurus