Hatzegopteryx

Hatzegopteryx Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Left humerus of the holotype specimen in ventral (A) and distal (B) view
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Pterosauria
Suborder:	†Pterodactyloidea
Family:	†Azhdarchidae
Subfamily:	† Quetzalcoatlinae
Genus:	†Hatzegopteryx Buffetaut et al., 2002
Type species
†Hatzegopteryx thambema Buffetaut et al., 2002

Hatzegopteryx ("

The first pterosaur remains from

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 Roșie locality of the Sebeș Formation, which is contemporary and adjacent to the Densuș Ciula Formation, a single large neck vertebra, the "RR specimen" or EME 215, was found.^[5][6] Although the lack of overlapping elements prevents this specimen from being definitely referred to Hatzegopteryx thambema, 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.^[8]

Description

Skull

The skull of Hatzegopteryx was gigantic, with an estimated length of 2.5 metres (8 ft 2 in) based on comparisons with Nyctosaurus and Anhanguera, making it one of the largest skulls among non-marine animals.^[4] The skull was broadened in the rear, being 0.5 metres (1 ft 8 in) wide across the quadrate bones.^[4] 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.^[1] In 2018, Mátyás Vremir concluded that Hatzegopteryx likely had a shorter and broader skull, the length of which he estimated at 1.6 metres (5 ft 3 in), and he also estimated its wingspan to be smaller than others at 8 metres (26 ft).^[9]

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seen in some other pterosaurs, including Pteranodon) that would have allowed the mouth to achieve a very wide gape.^[1] Unpublished remains attributed to Hatzegopteryx suggest that it had a proportionally short, deep beak, grouping with the "blunt-beaked" azhdarchids rather than the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 lawsoni).^[10]

Cervical vertebrae

A large neck vertebra attributed to Hatzegopteryx is short and unusually robust. The preserved portion measures 240 millimetres (9.4 in) long, with the entire vertebra likely measuring 300 millimetres (12 in) long in life.^[5] Pterosaurs had nine neck vertebrae.^[11] Regression indicates that the third to seventh cervical vertebrae would have collectively measured 1.508 metres (4 ft 11.4 in) in length, with the longest vertebra - the fifth - only measuring approximately 400 mm (16 in) long. Meanwhile, the same vertebrae in the similarly giant Arambourgiania measured 2.652 metres (8 ft 8.4 in). This indicates that the neck of Hatzegopteryx is about 50–60% the length of what would be expected for a giant azhdarchid of its size.^[8]

The bottom surface of the neck vertebra was also unusually thick, at 4 to 6 millimetres (0.16 to 0.24 in). For most other giant azhdarchids, including Arambourgiania, this surface is less than 2.6 millimetres (0.10 in) thick. Although the

The size of Hatzegopteryx was initially estimated by comparing the 236 mm (9.3 in) humerus fragment with that of Quetzalcoatlus northropi, which has a 544 mm (21.4 in)-long humerus. Observing that the Hatzegopteryx fragment presented less than half of the original bone, Buffetaut et al. established that it could possibly have been "slightly longer" than that of Quetzalcoatlus. The wingspan of the latter had been estimated at 11 to 12 metres (36 to 39 ft) in 1981. Earlier estimates had strongly exceeded this at 15 to 20 metres (49 to 66 ft). They concluded that an estimate of a 12 metres (39 ft) wing span for Hatzegopteryx was conservative, "provided that its humerus was longer than that of Q. northropi".[1]^[4] In 2010, Mark Witton and Michael Habib concluded that Hatzegopteryx was probably no larger than Q. northropi in wingspan. The initial conclusions did not account for distortion of the bone. The latter is generally estimated at 10–11 metres (33–36 ft) in length.^[12]

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.^[5] However, this is likely not true, since the neck vertebrae of large pterodactyloids generally tend to be wider and larger than the rest of the vertebrae. Although estimates of pterosaur size based on vertebrae alone are not particularly reliable, the size of this vertebra is consistent with an animal that measured 10 to 12 metres (33 to 39 ft) in wingspan.^[8]

Classification

Similarities between the humerus of Hatzegopteryx and

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

phylogenetic analysis conducted by Nicholas Longrich and colleagues in 2018 had recovered Hatzegopteryx within Azhdarchidae in a derived position, a sister taxon to both Arambourgiania and Quetzalcoatlus.^[15]

The cladogram of their analysis is presented below:

Azhdarchidae	Montanazhdarcho Azhdarcho Phosphatodraco Aralazhdarcho Eurazhdarcho aff. Quetzalcoatlus Zhejiangopterus Arambourgiania Hatzegopteryx Quetzalcoatlus

Paleobiology

Bone structure

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. Buffetaut et al. suggested that, in order to fly, the skull weight of Hatzegopteryx must have been reduced in some way. 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 millimetres (0.39 in) long, separated by a matrix of thin bony struts (trabeculae). The wing bones also bear a similar internal structure. This unusual construction differs from that of other pterosaurs, and more closely resembles the structure of expanded polystyrene (which is used to manufacture Styrofoam). This would have made the skull sturdy and stress-resistant, but also lightweight, enabling the animal to fly.^[1] A similar internal structure is also seen in the cervical vertebra referred to Hatzegopteryx.^[8]

Neck biomechanics

As a consequence of its robust, thick-walled vertebrae, the neck of Hatzegopteryx was much stronger than that of Arambourgiania. This can be quantified using relative failure force, which is the bone failure force of a vertebra divided by the body weight of the pterosaur that it belongs to, estimated at 180 to 250 kg (400 to 550 lb) for Arambourgiania and Hatzegopteryx. While Arambourgiania's neck vertebrae fail at about half of its body weight, the posterior neck vertebrae of Hatzegopteryx can withstand anywhere between five and ten body weights, depending on the loading of the bone. Even the hypothetically longer anterior neck vertebrae of Hatzegopteryx would be able to withstand four to seven body weights.^[8]

Although the centrum of Hatzegopteryx is much more robust than Arambourgiania, their ratios of bone radius to bone thickness (R/t)^[12] are roughly the same (9.45 for Hatzegopteryx and 9.9 for Arambourgiania). This may represent a compromise between increasing bending strength and buckling strength. Higher R/t ratios lead to improved bending strength, but weaker buckling strength. 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.^[8]

In order to support the robust head, the neck of Hatzegopteryx was likely strongly muscled. On the

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. These all serve as points of attachment for various muscles of the head and neck. Although not entirely unmuscled, the neck of Arambourgiania probably would not have been as extensively muscled as that of Hatzegopteryx.^[8]

Paleoecology

iguanodont Zalmoxes

Like all azhdarchid pterosaurs, Hatzegopteryx was probably a terrestrially foraging generalist predator.

theropods in the region) it has been suggested that Hatzegopteryx played the role of an apex predator in the Hațeg 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.^[16] 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.^[8] Another pterosaur, Thalassodromeus, has similarly been suggested to be raptorial.^[17]

Apart from Hatzegopteryx, there are various other unusual

hadrosaurid Telmatosaurus, and the iguanodontian Zalmoxes.^[21] Along with the nodosaurid Struthiosaurus, various small, fragmentary maniraptorans were present, including Bradycneme, Elopteryx, and Heptasteornis.^[21] Crocodilian remains, belonging to the genera Allodaposuchus, Doratodon, and Acynodon have also been found.^[23] Non-archosaurian components include the kogaionid multituberculate mammals Kogaionon, Barbatodon, Litovoi tholocephalos, and Hainina, ^[24][25] lizards such as the teiid Bicuspidon and the paramacellodid Becklesius, an unnamed madtsoiid snake, and the lissamphibians Albanerpeton, Eodiscoglossus, and Paradiscoglossus.^[26]

The importance of this fauna is a major geological justification for the designation of the area from 2004 to 2005 as Hațeg Country Dinosaurs Geopark, one of the earliest members of the European Geoparks Network, and (when the designation of UNESCO Global Geoparks was ratified in 2015) as Haţeg UNESCO Global Geopark.^[27]

During the Maastrichtian, southern Europe was an archipelago. The members of the Hațeg Island ecosystem lived on a landmass known as the Tisia–Dacia Block, of which the Hațeg Basin was a small part. This landmass was about 80,000 square kilometres (31,000 sq mi) in area, and was separated from other terrestrial terrains by stretches of deep ocean in all directions by 200 to 300 kilometres (120 to 190 mi).^[21] Being located at 27°N,^[28] the island was located farther south than the present-day latitude of 45°N. As such, the climate was likely subtropical, with distinct dry and wet seasons, and had an average temperature of about 25 °C (77 °F).^[29] The environment consisted of various alluvial plains, wetlands, and rivers,^[30] surrounded by woodlands dominated by ferns and angiosperms.^[21] Paleosols indicate a relatively dry Cretaceous climate, with an annual precipitation of less than 1,000 mm (39 in).^[29]

See also

• List of pterosaur genera
• Timeline of pterosaur research
• Pterosaur size

References

1. ^
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4. ^
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5. ^ ^{a b c d e} Vremir, M.M. (2010). "New faunal elements from the Late Cretaceous (Maastrichtian) continental deposits of Sebeș area (Transylvania)" (PDF). Acta Musei Sabesiensis. 2: 635–684.
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9. ^ Mátyás Vremir, Gareth Dyke, Zoltán Csikiá Sava, Dan Grigorescu & Eric Buffetaut, 2018, "Partial mandible of a giant pterosaur from the uppermost Cretaceous (Maastrichtian) of the Hațeg Basin, Romania", Lethaia
10. ^ Witton, M.; Brusatte, S.; Dyke, G.; Naish, D.; Norell, M.; Vremir, M. (2013). Pterosaur overlords of Transylvania: short-necked giant azhdarchids in Late Cretaceous Romania. The Annual Symposium of Vertebrate Paleontology and Comparative Anatomy. Edinburgh. Archived from the original on 6 April 2016. Retrieved 18 January 2017.
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13. ^ Witton, M.P.; Martill, D.M.; Loveridge, R.F. (2010). Clipping the Wings of Giant Pterosaurs: Comments on Wingspan Estimations and Diversity. Proceedings of the Third International Symposium on Pterosaurs. Acta Geoscientica Sinica. Vol. 31. Beijing. pp. 79–81. Archived from the original on 31 January 2017. Retrieved 18 January 2017.
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24. ^ Csiki, Z.; Grigorescu, D. (2000). "Teeth of multituberculate mammals from the Late Cretaceous of Romania". Acta Palaeontologica Polonica. 45 (1): 85–90.
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26. ^ Folie, A.; Codrea, V. (2005). "New lissamphibians and squamates from the Maastrichtian of Hațeg Basin, Romania". Acta Palaeontologica Polonica. 50 (1): 57–71.
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External links

Media related to Hatzegopteryx at Wikimedia Commons