A new giant pterosaur with a robust skull from the latest Cretaceous of Romania

Abstract

A new giant pterosaur, Hatzegopteryx thambema, nov.gen., nov.sp., from the Maastrichtian Densuş-Ciula Formation of Romania is remarkable for its very large size (estimated wing span > or = 12 m) and for the robustness of its large skull, which may have been nearly 3 m long. The stout skull bones contrast with the usually thin and slender skull elements of other pterosaurs, and raise the question of how the weight of the skull was reduced in order to make flight possible. The answer probably lies in the very peculiar internal structure of the bones, which consists of a dense network of very thin trabeculae enclosing small alveoli. This structure is reminiscent of expanded polystyrene and, like it, probably combined strength with lightness.

Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators

“…It can thus be referred to Azhdarchidae with confidence. We agree with Vremir (2010) that comparable size, anatomy, and geographical and geological provenance all indicate affinities with Hatzegopteryx , a robust giant azhdarchid first described from nearby Vălioara in the Haţeg Basin (Buffetaut, Grigorescu & Csiki, 2002; Buffetaut, Grigorescu & Csiki, 2003). We draw specific attention to the ventral bone wall of EME 315: at 4–6 mm thick, it is considerably thicker than the 2.6 mm or less reported from most other giant azhdarchids (including the giant Arambourgiania holotype cervical—Frey & Martill, 1996; Martill et al, 1998) but is comparable to bone walls of the H. thambema holotype humerus (Laboratory of Vertebrate Palaeontology, Geological and Geophysical Faculty, University of Bucharest, Romania) FGGUB R1083 (Buffetaut, Grigorescu & Csiki, 2003).…”

“…Our estimates indicate that giant azhdarchids included both Hatzegopteryx -like forms with short, wide necks, and Arambourgiania -like species with long, gracile necks. The former befits an animal with the unusually robust cranial anatomy known for H. thambema and is consistent with the view that this pterosaur was robust overall (Buffetaut, Grigorescu & Csiki, 2002; Buffetaut, Grigorescu & Csiki, 2003). As noted above, short necks have been postulated for a much smaller Romanian azhdarchid known from a likely cervical IV, LPV (FGGUB) R.2395 (Vremir et al, 2015).…”

“…A large, elongate cervical vertebra from the Maastrichtian of the French Pyrenees was also described as having thick bone walls of 2–6 mm (Buffetaut et al, 1997) so it is possible that this feature was more widespread in azhdarchids. The spongiose internal texture visible at the broken end of EME 315 also recalls the aberrant internal structure of the skull and humerus of the H. thambema holotype (Buffetaut, Grigorescu & Csiki, 2002). We consider Hatzegopteryx and EME 315 to possess a bone construction atypical among pterosaurs, and a close relationship between these specimens likely.…”

“…However, it may be that the thicker cortices of this bone enhanced buckling strength without drastically altering bending strength (Currey, 2002) or that its cross-sectional proportions are sufficient to provide high bending resistance alone. Such thick bone walls are not without precedent in pterosaurs—they appear in certain dsungaripterid limb bones (Fastnacht, 2005), a partial vertebra from another European azhdarchid (Buffetaut et al, 1997) and the Hatzegopteryx type material (Buffetaut, Grigorescu & Csiki, 2002; Buffetaut, Grigorescu & Csiki, 2003). Buckling resistance, as well as increased performance against compressive loading, has been posited as an explanation for this phenomenon (Fastnacht, 2005).…”

Review of taxonomy, geographic distribution, and paleoenvironments of Azhdarchidae (Pterosauria)

“…The Two Medicine locality for Montanazhdarcho minor and the Glen Rose locality for Radiodactylus langstoni are excluded here because these taxa are not azhdarchids. The records from the Bexen [=Montplasir] (Buffetaut et al 1996), Illd Formation, Upper Yezo Group (Obata et al 1972), and Kita-ama Formation, Izumi Group (Obata et al 2007) are excluded because the pterosaur material is too fragmentary and cannot be confidently attributed to Azhdarchidae. The Portezuelo Formation is excluded because the material cannot be determined beyond Azhdarchoidea indet.…”