Osteohistology of the Triassic Archosauromorphs Prolacerta, Proterosuchus, Euparkeria, and Erythrosuchus from the Karoo Basin of South Africa

Abstract

ABSTRACT The South African non-archosauriform archosauromorph Prolacerta and the archosauriforms Proterosuchus, Erythrosuchus, and Euparkeria were important constituents of the Early to early Middle Triassic Karoo ecosystem following the end-Permian mass extinction. We present new data on the osteohistology of these stem archosaurs and provide insight into their paleobiology. Bone tissues of the Early Triassic Prolacerta contain a poorly defined fibro-lamellar complex, with parallelfibered bone in some regions, whereas the contemporaneous Proterosuchus exhibits rapidly forming uninterrupted fibrolamellar bone early in its ontogeny, which becomes slow forming lamellar-zonal bone with increasing age. The early Middle Triassic Erythrosuchus deposited highly vascularized, uninterrupted fibro-lamellar bone throughout ontogeny, whereas the growth of the contemporaneous Euparkeria was relatively slow and cyclical. When our data are combined with those of previous studies, preliminary results reveal that Early an...