On the nature of the pteroid in pterosaurs

Abstract

The nature of the pteroid, a rod-like bone projecting from the carpus in pterosaurs, has long been disputed. Three lines of evidence, morphological, developmental and histological, indicate that the pteroid is a true bone, rather than ossified cartilage. The origin of the pteroid is unclear: it may be a modified carpal, the first metacarpal, or a neomorph.

First complete pterosaur from the Afro-Arabian continent: insight into pterodactyloid diversity

“…This bone is clearly articulated with the proximal syncarpal and directed towards the body. There has been a long discussion about the position of this unique pterosaur bone with the carpal elements 31–33 , which is clearly settled in the present specimen whose forelimb bones are perfectly articulated.

Figure 3 Mimodactylus libanensis gen. et sp. nov. ( a ) Skull and lower jaw.

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Biomechanics of the unique pterosaur pteroid

“…In such an orientation, depression of the pteroid could have deflected the propatagium and increased camber in the wing section, providing an increase in the maximum lift coefficient. It is also notable that available pteroid cross sections from across Pterosauria (Wellnhofer 1985;Unwin et al 1996) show that this bone had a suboval cross-section with the major axis in the mediolateral plane-the opposite of what might be expected from a bone that is loaded in dorsoventral bending. Such proportions might however be expected in a bone that is directed medially and forms the leading edge of the propatagium as this would minimize drag, a result that certainly applies across all pterodactyloid pterosaurs.…”

“…To provide a representative example for our analyses, we chose the Lower Cretaceous ornithocheirid Coloborhynchus robustus that had a 5.8 m wingspan (Wellnhofer 1991b;Unwin 2006;Wilkinson 2008). The pteroid of C. robustus (SMNK 1133PAL) is unusually well described (Unwin et al 1996) (figure 2a); we modelled its mechanics using a propatagium shape based on Wilkinson (2008) (figure 1c). …”

“…Irrespective of its articulation point, however, debates have centred on whether, or not, the pteroid supported the propatagial region of the pterosaur wing in flight by projecting forward in an anterior orientation (e.g. Hankin 1912;Frey & Riess 1981;Unwin et al 1996;Wilkinson et al 2006;Wilkinson 2007Wilkinson , 2008Unwin 2006) (figure 1a), or was orientated more parallel to the edge of the wing in a medial orientation (e.g. Wagner 1858; Hankin & Watson 1914;Padian 1984;Wellnhofer 1991a;Padian & Rayner 1993;Bennett 2007;Prondvai & Hone 2008) (figure 1b).…”

“…Hypotheses for pteroid function have been based on anatomical interpretations of well-preserved fossils (Pennycuick 1988;Unwin et al 1996;Frey et al 2003;Bennett 2007), theoretical consideration of aerodynamic performance advantages (Frey & Riess 1981) and on aerodynamic experiments using models (Wilkinson et al 2006). An anteriorly orientated reconstruction for the pteroid (Wilkinson 2007(Wilkinson , 2008 means that the propatagium must have extended distally from the pteroid to form, in dorsal profile, an elongate triangle to an attachment at the distal end of the wing metacarpal (figure 1c).…”