Post-hatchling cranial ontogeny in the Early Triassic diapsid reptile Proterosuchus fergusi

EZCURRA, M. D.; BUTLER, R. J.

JOURNAL OF ANATOMY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015

0021-8782

The phylogenetic position of Proterosuchus fergusi (Lower Triassic of South Africa) as one of the most basalarchosauriforms means that it is critically important for understanding the successful evolutionary radiation ofarchosaurs during the Mesozoic. The excellent sample of the species provides a unique opportunity tounderstand early archosauriform ontogeny. Qualitative and quantitative analyses of cranial ontogeneticvariation were conducted on an ontogenetic sequence, in which the smallest individual is 37% of the size ofthe largest one and osteohistological evidence suggests that four of 11 collected specimens had not reachedsexual maturity. Through ontogeny the skull of Proterosuchus became proportionally taller, the infratemporalfenestra larger, and the teeth more isodont and numerous but with smaller crowns. The sequence of somaticmaturity supports relatively high growth rates during early ontogeny. The skull of juvenile specimens ofProterosuchus closely resembles adults of the basal archosauromorph Prolacerta, whereas adult specimensresemble adults of more derived archosauriforms. As a result, a plausible hypothesis is that ontogeneticmodification events (e.g. heterochrony) may have been key drivers of the evolution of the general shape of theskull at the base of Archosauriformes. These changes may have contributed to the occupation of a newmorphospace by the clade around the Permo-Triassic boundary.