By G. S. Bever, Tyler R. Lyson, Daniel J. Field & Bhart-Anjan S. Bhullar
Transitional fossils informing the origin of turtles are among the most sought-after discoveries in paleontology1, 2, 3, 4, 5. Despite strong genomic evidence indicating that turtles evolved from within the diapsid radiation (which includes all other living reptiles6, 7), evidence of the inferred transformation between an ancestral turtle with an open, diapsid skull to the closed, anapsid condition of modern turtles remains elusive. Here we use high-resolution computed tomography and a novel character/taxon matrix to study the skull of Eunotosaurus africanus, a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles2, 3, 4.
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