Hatzegopteryx

Hatzegopteryx (“Hațeg basin wing”) is a genus of azhdarchid pterosaur found in the late Maastrichtian deposits of the Densuș Ciula Formation, outcropping in Transylvania, Romania. It is known only from the type species, Hatzegopteryx thambema, named by Buffetaut et al. in 2002 based on parts of the skull and humerus. Additional specimens, including a neck vertebra, were later placed in the genus, representing a range of sizes. The largest of these remains indicate it was among the biggest pterosaurs, with an estimated wingspan of 10 to 12 metres (33 to 39 ft).

Unusually among giant azhdarchids, Hatzegopteryx had a very wide skull bearing large muscular attachments; bones with a spongy internal texture instead of hollow; and a short, robust, and heavily muscled neck measuring 1.5 metres (4 ft 11 in) long, which was about half the length of other azhdarchids with comparable wingspans, and was capable of withstanding strong bending forces. Hatzegopteryx inhabited Hațeg Island, an island situated in the Cretaceous subtropics within the prehistoric Tethys Sea. In the absence of theropods, Hatzegopteryx was likely the apex predator of Hațeg Island, tackling proportionally larger prey (including dwarf titanosaurs and iguanodontians) than other azhdarchids.

Description

Skull

The skull of Hatzegopteryx was giant, with an estimated length of 3 metres (9.8 ft) based on comparisons with Nyctosaurus and Anhanguera, making it one of the largest skulls among non-marine animals. The skull was broadened in the rear, being 0.5 metres (1 ft 8 in) wide across the quadrate bones. While most pterosaur skulls are composed of gracile plates and struts, in Hatzegopteryx the skull bones are stout and robust, with large ridges indicating strong muscular attachments.

The massive jaw bore a distinctive groove at its point of articulation (also seen in some other pterosaurs, including Pteranodon) that would have allowed the animal to achieve a very wide gape. Unpublished remains attributed to Hatzegopteryx suggest that it had a proportionally short, deep beak, grouping with the “blunt-beaked” azhdarchids rather than the “slender-beaked” azhdarchids (including Quetzalcoatlus sp.).

Discovery and naming

The first remains of Hatzegopteryx were found from the upper part of the Middle Densuș Ciula Formation of Vălioara, northwestern Hațeg Basin, Transylvania, western Romania, which has been dated to the late Maastrichtian stage of the Late Cretaceous Period, around 66 million years ago. The holotype of Hatzegopteryx, FGGUB R 1083A, consists of two fragments from the back of the skull and the damaged proximal part of a left humerus. One of these fragments, namely the occipital region, was initially referred to a theropod dinosaur when it was first announced in 1991. A 38.5 cm (15.2 in) long middle section of a femur found nearby, FGGUB R1625, may also belong to Hatzegopteryx. FGGUB R1625 would have belonged to a smaller individual of Hatzegopteryx (assuming it pertains to the genus), with a 5 to 6 m (16 to 20 ft) wingspan. Additional reported specimens from the locality include an unpublished mandible, also from a large individual.

Map showing diverse Late Cretaceous azhdarchid assemblages worldwide
Image rendering courtesy of Mark Witton; map imagery by kind permission of Ron Blakey, Colorado Plateau Geosystems, Inc. Outdated Hatzegopteryx silhouette has been replaced with newer one by Witton.
Map to show the global distribution of faunas containing small-medium and giant-sized azhdarchids, evidence for niche partioning. Temporal range: Late Cretaceous, 108–66 Ma

New specimens of Hatzegopteryx have since been recovered from other localities. In the Sânpetru Formation from the locality of Vadu, Sântămăria-Orlea, a medium-sized scapulocoracoid was found, which probably pertained to an individual with a wingspan of 4.5 to 5 m (15 to 16 ft). From the Râpa Roşie locality of the Sebeş Formation, which is contemporary and adjacent to the Densuș Ciula Formation, a single large neck vertebra, the “RR specimen” or EME 215, was found. Although the lack of overlapping elements prevents this specimen from being definitely referred to Hatzegopteryx thambena, its distinctive internal bone structure, as well as the lack of evidence for a second giant azhdarchid in the area, warrant its referral to at least H. sp.

Hatzegopteryx was named in 2002 by French paleontologist Eric Buffetaut, and Romanian paleontologists Dan Grigorescu and Zoltan Csiki. The generic name is derived from the Hatzeg (or Hațeg) basin of Transylvania, where the bones were found, and from Greek pteryx (ἡ πτέρυξ, -υγος (also ἡ πτερύξ, -ῦγος), or ‘wing’. The specific name thambema is derived from the Greek for ‘terror, monster’ (τό θάμβημα, -ήματος), in reference to its huge size.

Classification

Similarities between the humerus of Hatzegopteryx and Quetzalcoatlus northropi have been noted; both have a long, smooth deltopectoral crest, and a thickened humeral head. These were initially the basis of the taxon’s referral to the clade Azhdarchidae, but they are also similar enough to be a basis for the synonymy of Hatzegopteryx and Quetzalcoatlus. However, this is likely due to the relatively non-diagnostic nature of the humerus in giant azhdarchid taxonomy, and the lack of a detailed description for the elements of Q. northropi. However, the neck and jaw anatomy of Hatzegopteryx is quite clearly distinct from the smaller Q. sp., which warrants the retention of Hatzegopteryx as a taxon separate from Quetzalcoatlus.

The neck vertebra referred to Hatzegopteryx sp. contains a number of traits that allow for it to be definitely identified as that of an azhdarchid. The centrum is relatively low, the zygapophyses are large and flattened, and the preserved portions of the neural spine indicate that it is bifid, or split into two.

Paleoecology

Like all azhdarchid pterosaurs, Hatzegopteryx was probably a terrestrially foraging generalist predator. It is significantly larger than any other terrestrial predator from Maastrichtian Europe; due to its large size in an environment otherwise dominated by island dwarf dinosaurs, with no large hypercarnivorous theropods in the region, it has been suggested that Hatzegopteryx played the role of an apex predator in the Haţeg Island ecosystem. The robust anatomy of Hatzegopteryx suggests that it may have tackled larger prey than other azhdarchids, including animals too large to swallow whole; similarly, some modern storks (particularly the marabou stork and the jabiru) are known to attack and kill large prey such as flamingoes, and occasionally children, with their beaks. Meanwhile, other giant azhdarchids like Arambourgiania would probably have instead fed on small prey (up to the size of a human), including hatchling or small dinosaurs and eggs. Another pterosaur, Thalassodromeus, has similarly been suggested to be raptorial.

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