Abstract

The bone histology of non-archosauriform archosauromorphs is poorly known relative to archosauriforms, especially ornithodiran (bird-line) archosaurs. Here we describe the femoral and tibial histology of a single individual of Stenaulorhynchus stockleyi, a Middle Triassic rhynchosaur from Tanzania. Both elements are composed largely of moderately vascularized parallel-fibered bone tissue, which becomes avascular and more lamellar approaching the periosteum. The spacing between growth marks in S. stockleyi strongly attenuates with age, suggesting determine growth for this taxon. Whereas the bone tissue suggests slower growth compared to South American rhynchosaurs, which have fibro-lamellar bone tissue and exhibit more anastomoses between canals, the determinate growth pattern seems to be shared among hyperodapedontid rhynchosaurs. Although non-archosauriform archosauromorphs vary in the rate of bone deposition and growth in their first year, all taxa examined to date grew relatively slowly compared to most archosauriforms, especially ornithodiran archosaurs.