Hatzegopteryx

Hatzegopteryx ("Haţeg basin wing") is a genus of azhdarchid pterosaur, known from incomplete remains found in Transylvania. The skull fragments, left humerus, and other fossilized remains indicate a huge animal with a wingspan of 12 meters (40 ft) or more. It is known from only the type species, Hatzegopteryx thambema. The generic name derives from the Hatzeg (or Haţeg) basin of Transylvania where the bones were found, and from the Greek pteryx, or 'wing'. The specific name thambema derives from the Greek for 'monster', in reference to its huge size.

Hatzegopteryx hails from the Densus-Ciula Formation of western Romania, which has been dated to the late Maastrichtian stage of the late Cretaceous Period, around 65 million years ago. A 35.5 centimeter femur found nearby may also have belonged to Hatzegopteryx.

Skull
Hatzegopteryx apparently had a robust skull broadened in the rear, and a massive jaw. Its lower jaw featured a unique groove in its point of articulation, also seen in some other pterosaurs, that would have allowed the animal to achieve a very wide gape. Many of the fossilized bones of Hatzegopteryx closely resemble those of the closely related Quetzalcoatlus, though in Hatzegopteryx the skull was much more heavily built, and had a markedly different jaw articulation similar to that seen in Pteranodon. Based on comparisons with other pterosaurs, Buffetaut and colleagues (who initially described the specimens) estimated that the skull of Hatzegopteryx was probably almost 3 m (9.8 ft) in length, which would have made it larger than that of the largest Quetzalcoatlus species and among the largest skulls of any known non-marine animals.

The skull of Hatzegopteryx was also unique in its heavy, robust construction. Most pterosaur skulls are made up of very lightweight plates and struts. In Hatzegopteryx, the skull bones are stout and robust, with large-ridged muscle insertion areas. In their 2002 description, Buffetaut and colleagues suggested that in order to fly, the skull weight of this pterosaur must have been reduced in some unconventional way (while they allowed that it could have been flightless, they found this unlikely due to the similarity of its wing bones to flying pterosaurs). The authors theorized that the necessary weight reduction was accomplished by the internal structure of the skull bones, which were full of small pits and hollows (alveoli) up to 10mm long, separated by a matrix of incredibly thin bony struts (trabeculae), a feature also found in some parts of Hatzegopteryx wing bones. The authors pointed out that this unusual construction, which differed significantly from the irregular internal structure of other pterosaur skulls, resembles the structure of expanded polystyrene, the substance used to make Styrofoam. They noted that this would allow a sturdy, stress-resistant construction while remaining lightweight, and would have allowed the huge-headed animal to fly.