Meeting Abstract

40.6  Tuesday, Jan. 5  The unique pterosaur pteroid bone: wing function in extinct flying reptiles DYKE, Gareth*; PALMER, Colin; University College Dublin; University of Bristol gareth.dyke@ucd.ie

Pterosaurs, flying reptiles from the Mesozoic, had wing membranes that were supported by the bones of their arm and a super-elongate fourth finger (the ‘wing-finger’). Associated with the wing, pterosaurs also possessed an unique bone – the pteroid – that functioned to support the forward part of the membrane (the propatagium) in front of its leading edge, articulated at the wrist. Because reconstructed orientations for the pterosaur pteroid vary (i.e. lying anterior to the wing leading edge or medial, alongside it) and cause considerable debate, we undertook to provide bounds on its mechanical strength and aerodynamic performance by biomechanical modelling. Finding the most likely orientation for the pteroid is important because its position implies differences in the way that pterosaurs controlled their wings. Our analysis of pterosaur wrist biomechanics and bone cortical thickness shows that an anteriorly orientated pteroid, at least in large ornithocheirid pterosaurs, is highly unlikely. Unless these pterosaurs only flew steadily and low speeds and had very low body masses (another source of contention), their pteroids would have broken if pointed forward (anteriorly) from the wing leading edge. In addition to this structural vulnerability, the degree of pteroid movement required to produce a forward orientation would have required impractically high membrane strains and theresultant leading edge shape would have reduced the aerodynamic performance of the wings. We demonstrate quantitatively that the more traditional medial orientation for the pterosaur pteroid was mechanically much more robust and more aerodynamically efficient and speculate on the evolution of the wing in these remarkable extinct flying reptiles.