Hatzegopteryx ("Hațeg basin wing") is a genus of azhdarchid pterosaur found in the late Maastrichtian deposits of the Densuş Ciula Formation, an outcropping in Transylvania, Romania.

It is known only from the type species, Hatzegopteryx thambema, named by paleontologists Eric Buffetaut, Dan Grigorescu, and Zoltan Csiki in 2002 based on parts of the skull and humerus.

Unusually among giant azhdarchids, Hatzegopteryx had a very wide skull bearing large muscular attachments, bones with a spongy internal texture instead of being hollow, and a short, robust, and heavily muscled neck measuring 1.5 m (5 ft) long, which was about half the length of other azhdarchids with comparable wingspans and was capable of withstanding strong bending forces.

In the absence of large theropods, Hatzegopteryx was likely the apex predator of Hațeg Island, tackling proportionally larger prey (including dwarf titanosaurs and iguanodontians) than other azhdarchids.

The specific name thambema is derived from the Greek word for “terror” or “monster” (τό θάμβημα, -ήματος[7]), in reference to its huge size.

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).

Observing that the Hatzegopteryx fragment presented less than half of the original bone, Buffetaut and colleagues established that it could possibly have been "slightly longer" than that of Quetzalcoatlus.

[9] It has been suggested (on the basis of the wide and robust neck vertebra referred to Hatzegopteryx) that the entire vertebral column of the animal was similarly expanded, increasing its overall size.

[10] 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 mouth to achieve a very wide gape.

[8] Similarities between the humerus of Hatzegopteryx and Quetzalcoatlus northropi have been noted, as both of them have a long, smooth deltopectoral crest and a thickened humeral head.

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 at the time of the assignment.

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 in half.

[8] A phylogenetic analysis conducted by paleontologist Nicholas Longrich and colleagues in 2018 had recovered Hatzegopteryx in a derived (advanced) position within Azhdarchidae.

Azhdarcho lancicollis Albadraco tharmisensis Aerotitan sudamericanus Mistralazhdarcho maggii Aralazhdarcho bostobensis Phosphatodraco mauritanicus Eurazhdarcho langendorfensis Zhejiangopterus linhaiensis Wellnhopterus brevirostris Cryodrakon boreas Hatzegopteryx thambema Arambourgiania philadelphiae Quetzalcoatlus lawsoni Quetzalcoatlus northropi Topology 2: Pêgas and colleagues (2023).

While the skull of Hatzegopteryx was unusually large and robust, its wing bones are comparable to those of other flying pterosaurs, indicating that it was not flightless at all.

The necessary weight reduction may have been accomplished by the internal structure of the skull bones, which were full of small pits and hollows (alveoli) up to 10 mm (0.39 in) long, separated by a matrix of thin bony struts (trabeculae).

To compensate for this, Hatzegopteryx shows a number of other adaptations to improve buckling strength, namely the distinctive internal structures of the bones and the large articular joints of the vertebrae, the latter of which helps to distribute stress.

Likewise, the opisthotic process, neural spines, and zygapophyses all appeared to have been large and robust (with the latter bearing many pits and edges that likely represent muscle scars), and the basioccipital tuberosities were long.

The robust anatomy of Hatzegopteryx suggests that it may have tackled larger prey than other azhdarchids, including animals too large to swallow whole.

[21] The robust, flightless, and possibly herbivorous avialan[22] or dromaeosaurid[23] Balaur, which had two enlarged claws on each foot,[23] represents another highly specialized component of the fauna.

The ecosystem contained a number of insular dwarfs, namely the titanosaurs Magyarosaurus[24] and Paludititan,[25] the hadrosaurid Telmatosaurus, and the iguanodontian Zalmoxes.

[26] Non-archosaurian components include the kogaionid multituberculate mammals Kogaionon, Barbatodon, Litovoi tholocephalos, and Hainina,[27][28] lizards such as the teiid Bicuspidon and the paramacellodid Becklesius, an unnamed madtsoiid snake, and the lissamphibians Albanerpeton, Eodiscoglossus, and Paradiscoglossus.