Hatzegopteryx

*Hatzegopteryx thambema*

Tim Bradley Artwork

***Hatzegopteryx*** (meaning "Hațeg basin wing") is a genus of azhdarchid pterosaur, known from incomplete remains found in Transylvania. The skull fragments, left humerus, and other fossilised remains indicate it was the largest pterosaur. The skeleton of *Hatzegopteryx* has been considered identical to the known remains of *Quetzalcoatlus*. 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*.

## 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 Additional reported specimens from the locality include an unpublished mandible, also from a large individual.

*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.

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.*

## Description

### 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 strutsTemplate:Fact. 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.

### 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. Pterosaurs had nine neck vertebrae;[5] 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.[6]

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 neural spine of the vertebra is not completely preserved, the width of the preserved portion suggests that it was relatively tall and robust relative to those of other pterosaurs. Other aspects of the vertebra converge upon the seventh neck vertebra of the smaller *Azhdarcho* most closely: the articulating sockets (cotyles) are much shallower than the neural arches, and are four times as wide as they are tall; a process on the bottom of the vertebrae, known as a hypapophysis, is present; the processes at the front of the vertebrae, the prezygapophyses, are splayed; and the vertebra has a tapered "waist" in the middle of the centrum. Although initially identified as a third neck vertebra,[4] these traits supports the identification of the vertebra as coming from the rear of the neck, more specifically as being the seventh vertebra.

### Size

The authors estimated the size of *Hatzegopteryx* by comparing the humerus fragment, 236 mm (9.3 in) long, with that of *Quetzalcoatlus*, of which specimen TMM 41450-3 has a 544 mm (1 ft 9.4 in) long humerus. Observing that the *Hatzegopteryx* fragment presented less than half of the original bone, they established that it could possibly have been "slightly longer" than that of *Quetzalcoatlus*. They noted that the wing span of the latter had in 1981 been estimated at 11 to 12 metres (36–39 ft), while earlier estimates had strongly exceeded this at 15 to 20 metres (49-65.6 ft). From this they concluded that an estimate of a 12 metre (39 ft) wing span for *Hatzegopteryx* was conservative "if its humerus was indeed somewhat longer than that of Q. northropi". In 2003 they moderated the estimates to a close to 12 metres (39 ft) wing span and an over 2.5 m (8 ft 2 in) skull length. In 2010 Mark Witton e.a. stated that any appearance that the *Hatzegopteryx* humerus was bigger than TMM 41450-3 had been caused by a distortion of the bone after deposition and that the species thus likely had no larger wingspan than *Quetzalcoatlus*, today generally estimated at 10 to 11 metres (33–36 ft).

## 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.

## 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. 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 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 resembles more closely the structure of expanded polystyrene (used to manufacture Styrofoam). This would have made the skull sturdy and stress-resistant, but also lightweight, enabling the animal to fly. A similar internal structure is also seen in the cervical vertebra referred to *Hatzegopteryx*.

### 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, 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 to 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.

Although the centrum of *Hatzegopteryx* is much more robust than *Arambourgiania*, their ratios of bone radius to bone thickness (R/t) 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.

In order to support the robust head, the neck of *Hatzegopteryx* was likely strongly muscled. On the occipital bones, the nuchal lines, which serve as muscular attachments, are very well-developed and bear prominent scars. These conceivably supported the transversospinalis muscles, which aid in extension and flexion of the head and neck. 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; 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*.

## 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.

Apart from *Hatzegopteryx*, there are various other unusual denizens of the Haţeg Island ecosystem. Co-occurring pterosaurs included the small azhdarchid *Eurazhdarcho*, with a wingspan of 3 m (9.8 ft); an unnamed, small-sized short-necked azhdarchid with a wingspan of 3.5 to 4 metres (11 to 13 ft); a somewhat larger and likewise unnamed azhdarchid, with a wingspan of 5 m (16 ft); and apparently small pteranodontids have been found as well. The robust, flightless, and possibly herbivorous avialan or dromaeosaurid *Balaur*, which had two enlarged claws on each foot, represents another highly specialized component of the fauna. The ecosystem contained a number of insular dwarfs, namely the titanosaurs *Magyarosaurus* and *Paludititan*, the hadrosaurid *Telmatosaurus*, and the iguanodontian *Zalmoxes*. Along with the nodosaurid *Struthiosaurus*, various small, fragmentary maniraptorans were present: *Bradycneme*, *Elopteryx*, and *Heptasteornis*. Crocodilian remains, belonging to the genera *Allodaposuchus*, *Doratodon*, and *Acynodon* have also been found. Non-archosaurian components include the kogaionid multituberculate mammals *Kogaionon*, *Barbatodon*, *Litovoi tholocephalos*, and *Hainina*; lizards such as the teiid *Bicuspidon* and the paramacellodid *Becklesius*; an unnamed madtsoiid snake; and the lissamphibians *Albanerpeton*, *Eodiscoglossus*, and *Paradiscoglossus*.

During the Maastrichtian, southern Europe was an archipelago. The members of the Haţeg Island ecosystem lived on a landmass known as the Tisia–Dacia Block, of which the Haţeg 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). Being located at 27°N, the island was located farther south than the present-day latitude of 45°N; the climate was likely subtropical, with distinct dry and wet seasons, and an average temperature of about 25 °C (77 °F). The environment consisted of various alluvial plains, wetlands, and rivers, surrounded by woodlands dominated by ferns and angiosperms. Paleosols indicate a relatively dry Cretaceous climate, with an annual precipitation of less than 1,000 mm (39 in).

## Appearance in other media

### *Jurassic Park*

* *Hatzegopteryx* appears in Jurassic World: The Game and Jurassic World: Alive as a common pterosaur.

## References

1. ↑ 1.0 1.1 Buffetaut, E., Grigorescu, D., and Csiki, Z. (2002). "A new giant pterosaur with a robust skull from the latest Cretaceous of Romania." *Naturwissenschaften*, **89**(4): 180-184. Abstract