Procolophonoidea: Morphology

All procolophonoids share a few unique derived characters that demonstrate that they are closely related to each other. These include (pictured below for your enjoyment):

Skull of the Lower Triassic procolophonoid Owenetta. Abbreviations: O. f., concave occipital flange of the squamosal; P. e., posterior extension of the orbit; Prf. pr., medial process of the prefrontal; V. e., ventral emargination of the cheek.

Characters unique to procolophonoids and turtles that suggest close relationships between these two groups include:

A skull of Procolophon from the UCMP collections. The large hole between the orbits is a pineal foramen, a primitive character lost in extant anapsids.


Gauthier, J., A. G. Kluge, and T. Rowe. 1988. The early evolution of the Amniota. In: M. J. Benton (ed.) The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds: 103-155. Oxford: Clarendon Press.

Lee, M. The turtle's long-lost relatives. Natural History, April 1994 1994, 63-65.

Reisz, R. R. and M. Laurin. 1991. Owenetta and the origin of turtles. Nature 349: 324-326.