Primates and engineering principles: Applications to craniodental mechanisms in ancient terrestrial predators

Abstract

Ancient terrestrial tetrapod ecosystems of the Permian Period document the expansion and diversification of the earliest carnivore guilds containing highly specialised killers. These predators were synapsids, the ancient ancestors of mammals. Determining the mode of life of fossils such as synapsids is fraught with difficulties. But developments in the past twenty years provide rigorous new approaches for ascertaining habit in extinct tetrapods. A synthetic-analytical coupling of appropriate experimental data with the hybrid numerical computer technique Finite Element Analysis (FEA) gives a robust interpretation of synapsid morphology. Applying these techniques to Late Permian predators refines our knowledge of carnivore habit and niche separation at this crucial stage in carnivore evolutionary history. The Synapsida dominated late Permian terrestrial ecosystems, and forms such as lycosuchids, scylacosaurids and gorgonopsids composed the bulk of the tetrapod predators. Their postcranial skeletons are very similar and provide few indications of ecological partitioning; synapsid skulls however show a great diversity of form.

Unlike many extinct tetrapods such as dinosaurs, synapsids are structurally closely comparable to a group of living amniotes: mammals. This is crucial as extensive experimental data on skull structure in mammals can be appropriately applied to synapsid cranial anatomy in a meaningful way. This is less so in, for example a scaled-up use of lizard skulls to interpret cranial function in theropod dinosaurs. Of particular use in this analysis of synapsid crania are the detailed experimental analyses of jaw and skull design in living primates. Stress-strain analyses of the mandible in primates allow a rigorous interpretation of jaw function in synapsids. This approach reveals some hitherto unknown aspects of the morphology and hence potential niche separation of these carnivores during the Permo-Triassic extinction event. In at least one instance, niche filling appears to have been based on a specific trophic ecotype: the gorgonopsid — moschorhinid convergence. The data is tied together by using FEA to examine stress patterns in fossil skulls. By using a synthetic-analytical approach, an interpretation of the cranial morphology of synapsid carnivores is produced of sufficient depth so that their niche separation based on predatory capability can be elucidated. Results provide insights into aspects of Permo-Triassic synapsid predator communities.