Australothyris

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Australothyris is an extinct, early parareptile from the Middle Permian period (about 265–260 million years ago) found in what is now South Africa. The only species known is Australothyris smithi.

The fossil comes from the Tapinocephalus Assemblage Zone of the upper Abrahamskraal Formation. It was discovered in 1995 by Robert Smith at Beukesplaas farm and is known from a single specimen (SAM-PK-K8302) that includes most of a skull and parts of the skeleton.

Australothyris was originally misidentified as Owenetta, but a later study revealed a skull opening behind the eyes (a temporal fenestra) and recognized it as a new genus and species in 2009. The name means “southern opening,” highlighting the idea that parareptiles may have originated in Gondwana (the southern landmass) and had temporal openings early in their evolution.

As the most basal member of the group Procolophonomorpha, Australothyris helped scientists understand the early history of this lineage. It has several distinctive features, such as a very high tooth count in the upper jaw (31 teeth in the maxilla), a long rear part of the postfrontal bone, a large temporal opening surrounded by several skull bones, and a palate with several notable teeth and ridges. Its skull and jaw structure provide important clues about how early parareptiles looked and functioned.

Its position in early analyses suggested Australothyris was the first branch of Procolophonomorpha, implying that this group originated with a large temporal opening. However, later finds like Microleter from Oklahoma and some millerettids with openings in the skull have complicated that story, indicating a more complex evolution for temporal openings and the geographic origin of procolophonomorphs.

Overall, Australothyris is important because it offers a glimpse into the earliest stages of procolophonomorph evolution and the broader story of how early parareptiles spread and diversified.