Introduction to Procolophonoidea

A Permo-Triassic group of Anapsids

Procolophonoids (PRO-col-oh-phon-oids) are an extinct group of anapsids known from the Upper Permian and the Triassic. They had a nearly cosmopolitan distribution and have been found in North America, Europe, Asia, Africa, and Antarctica. The affinities of procolophonoids have long been debated. They were at some point thought to be close relatives of the clade Reptilia (the smallest group that includes turtles, diapsids, and their most recent common ancestor), but they are now considered to be most closely related to turtles, as shown by the presence of a large posttemporal fenestra (an opening in the back of the skull through which the jaw muscles of turtles exit the skull). Their exact position in Anapsida is still controversial. Some consider procolophonoids to be the closest known extinct relatives of turtles, while others think that pareiasaurs are more closely related to turtles.

Skull of the Lower Triassic procolophonoid Owenetta from South Africa. A, dorsal view. B, palatal view. C, right lateral view. D, occipital view. E, lateral view of the lower jaw. F, medial view of the same. Abbreviations: P. f., posttemporal fenestra; Q. e., quadrate emargination.

All known Upper Permian and some Lower Triassic procolophonoids had sharp teeth and hence were almost certainly either insectivorous or carnivorous, but Middle and Upper Triassic forms have broad, bulbous teeth that probably were used to process a herbivorous diet. The Upper Triassic procolophonoids include taxa with strange skulls, like Hypsognathus.

The presence of a deep quadrate emargination (see the picture below) and a slender stapes (a sound-conducting middle ear ossicle) suggests that procolophonoids had a tympanum (ear drum) and could hear high frequency airborne sounds.

If you're interested in taking a closer look at the Procolophono idea, try our Procolophonoidea Morphology page.

A skull of Procolophon in lateral view showing the deep quadrate emargination that supported the tympanum. This is located at the rear of the skull, between the lower jaw and the top of the skull.