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Proterosuchus (Early Triassic diapsid) post-hatchling cranial ontogeny

Ben Creisler

A new paper:

Martín D. Ezcurra and Richard J. Butler (2015)
Post-hatchling cranial ontogeny in the Early Triassic diapsid reptile
Proterosuchus fergusi.
Journal of Anatomy (advance online publication)
DOI: 10.1111/joa.12300

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