May 11, 2016

Highlights

The origin of turtles has long remained cryptic due to a relative lack of clearly informative transitional fossils.
Euntosaurus africanus is a Middle Permian amniote from South Africa that helps fill this transitional role.
μCT analysis of Eunotosaurus skull reveals an upper temporal fenestra, potentially homologous with that of other living reptiles.
Preliminary analysis of other early amniotes reveals considerable variation in cranial roof architecture.
Advanced imaging holds great promise in clarifying the deep-time origin of modern amniote clades.

Abstract

Fossils provide a glimpse into the architecturally complex origins of modern vertebrate body plans. One such origin that has been long debated is that of turtles. Although much attention has been directed toward the origin of the shell, the enigmatic evolution of the turtle skull and its anapsid temporal region has long clouded our understanding of reptile phylogeny. Two taxa, Eunotosaurus africanus and Pappochelys rosinae, were recently and independently described as long-anticipated stem turtles whose diapsid skulls would cement the evolutionary link between turtles and other modern reptile lineages. Detailed μCT analysis of the stratigraphically older and phylogenetically stemward of the two, Eunotosaurus, provides empirical insight into changing developmental trajectories that may have produced the anapsid cranial form of modern turtles and sets the stage for more comprehensive studies of early amniote cranial evolution.