| Hatzegopteryx | |
|---|---|
 | |
| Left humerus of theholotype 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 ("Hațeg basin wing") is agenus ofazhdarchidpterosaur found in the lateMaastrichtian deposits of theDensuş Ciula Formation, an outcropping inTransylvania,Romania. It is known only from thetype species,Hatzegopteryx thambema, named by paleontologists Eric Buffetaut, Dan Grigorescu, and Zoltan Csiki in 2002 based on parts of the skull andhumerus. Additional specimens, including aneck 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 m (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 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.Hatzegopteryx inhabitedHațeg Island, an island situated in theCretaceous subtropics within the prehistoricTethys Sea. In the absence of largetheropods,Hatzegopteryx was likely theapex predator of Hațeg Island, tackling proportionally larger prey (including dwarftitanosaurs andiguanodontians) than other azhdarchids.
The first pterosaur remains fromRomania were identified byFranz Nopcsa in 1899, and the first remains ofHatzegopteryx were found during a student dig in the late 1970s from the upper part of the MiddleDensuş Ciula Formation ofVălioara, northwesternHațeg Basin,Transylvania, westernRomania, which has been dated to the lateMaastrichtian stage of theLate CretaceousPeriod, around 66 million years ago. Theholotype ofHatzegopteryx, FGGUB R 1083A, consists of two fragments from the back of the skull and the damaged proximal part of a left humerus.[1] One of these fragments, namely theoccipital region, was initially referred to atheropoddinosaur when it was first announced in 1991.[2][3] A 38.5 cm (15.2 in) long midsection of afemur found nearby, FGGUB R1625, may also belong toHatzegopteryx.[4] FGGUB R1625 would have belonged to a smaller individual ofHatzegopteryx (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 unpublishedmandible, also from a large individual.[5][6]
Hatzegopteryx was named in 2002 by Frenchpaleontologist Eric Buffetaut and Romanian paleontologists Dan Grigorescu and Zoltan Csiki. Thegeneric name is derived from theHatzeg (orHațeg) basin of Transylvania, where the bones were found, and from theGreek wordpteryx (πτέρυξ) “wing”. Thespecific namethambema is derived from Greekthambema (θάμβημα) “terror, monster”, in reference to its huge size.[1]
New specimens ofHatzegopteryx have since been recovered from other localities. In theSânpetru Formation from the locality of Vadu,Sântămăria-Orlea, a medium-sizedscapulocoracoid 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 theSebeș 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 toHatzegopteryx 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 leastH. sp.[7]
The size ofHatzegopteryx was initially estimated by comparing the 236 mm (9.3 in) humerus fragment with that ofQuetzalcoatlus northropi, which has a 544 mm (21.4 in)-long humerus. Observing that theHatzegopteryx fragment presented less than half of the original bone, Buffetaut and colleagues established that it could possibly have been "slightly longer" than that ofQuetzalcoatlus. The wingspan of the latter had been estimated at 11 to 12 m (36 to 39 ft) in 1981. Earlier estimates had strongly exceeded this at 15 to 20 m (49 to 66 ft). They concluded that an estimate of a 12 m (39 ft) wing span forHatzegopteryx was conservative, "provided that its humerus was longer than that ofQ. northropi".[1][4] In 2010,Mark Witton and Michael Habib concluded thatHatzegopteryx was probably no larger thanQ. northropi in wingspan. The initial conclusions did not account for distortion of the bone. The latter is generally estimated at 10 to 11 m (33 to 36 ft) in length.[8]
It has been suggested (on the basis of the wide and robust neck vertebra referred toHatzegopteryx) 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 largepterodactyloids 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 m (33 to 39 ft) in wingspan.[7]
The skull ofHatzegopteryx was gigantic, with an estimated length of 2.5 m (8 ft 2 in) based on comparisons withNyctosaurus andAnhanguera, making it one of the largest skulls among non-marine animals.[4] The skull was broadened in the rear, being 0.5 m (1 ft 8 in) wide across thequadrate bones.[4] While most pterosaur skulls are composed of gracile plates and struts, inHatzegopteryx, the skull bones are stout and robust, with large ridges indicating strong muscular attachments.[1] In 2018,Mátyás Vremir concluded thatHatzegopteryx likely had a shorter and broader skull, the length of which he estimated at 1.6 m (5 ft 3 in), and he also estimated its wingspan to be smaller than others at 8 m (26 ft).[9]
The massive jaw bore a distinctive groove at its point of articulation (also seen in some other pterosaurs, includingPteranodon) that would have allowed the mouth to achieve a very wide gape.[1] Unpublished remains attributed toHatzegopteryx suggest that it had a proportionally short, deep beak, grouping with the "blunt-beaked"azhdarchids rather than the "slender-beaked" azhdarchids, the latter containingQuetzalcoatlus sp. (now known as the speciesQ. lawsoni[10]).[11]
A largeneck vertebra attributed toHatzegopteryx is short and unusually robust. The preserved portion measures 240 mm (9.4 in) long, with the entire vertebra likely measuring 300 mm (12 in) long in life.[5] Pterosaurs had nine neck vertebrae.[12] Regression indicates that the third to seventh cervical vertebrae would have collectively measured 1.508 m (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 giantArambourgiania measured 2.652 m (8 ft 8.4 in). This indicates that the neck ofHatzegopteryx is about 50–60% the length of what would be expected for a giant azhdarchid of its size.[7]
The bottom surface of the neck vertebra was also unusually thick, at 4 to 6 mm (0.16 to 0.24 in). For most other giant azhdarchids, includingArambourgiania, this surface is less than 2.6 mm (0.10 in) thick. Although theneural 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 smallerAzhdarcho 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, theprezygapophyses, are splayed, and the vertebra has a tapered "waist" in the middle of thecentrum.[7] Although initially identified as a third neck vertebra,[5] these traits supports the identification of the vertebra as coming from the rear of the neck, more specifically as being the seventh vertebra.[7]
Similarities between the humerus ofHatzegopteryx andQuetzalcoatlus northropi have been noted, as both of them have a long, smooth deltopectoral crest and a thickenedhumeral head. These were initially the basis of the taxon's referral to the clade Azhdarchidae,[1] but they are also similar enough to be a basis for thesynonymy ofHatzegopteryx andQuetzalcoatlus. 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 ofQ. northropi at the time of the assignment.[13] However, the neck and jaw anatomy ofHatzegopteryx is quite clearly distinct from the smallerQ. lawsoni, which warrants the retention ofHatzegopteryx as a taxon separate fromQuetzalcoatlus.[1][7][14]
The neck vertebra referred toHatzegopteryx sp. contains a number of traits that allow for it to be definitely identified as that of an azhdarchid. The centrum is relatively low, thezygapophyses are large and flattened, and the preserved portions of the neural spine indicate that it is bifid, or split in half.[7] Aphylogenetic analysis conducted by paleontologist Nicholas Longrich and colleagues in 2018 had recoveredHatzegopteryx in a derived (advanced) position within Azhdarchidae.[15] This placement is corroborated in subsequent phylogenetic analyses by Brian Andres in 2021 and by Rodrigo Pêgas and colleagues in 2023. They both foundHatzegopteryx within the subfamily Quetzalcoatlinae, albeit in different positions. Andres found it in aclade withArambourgiania andQuetzalcoatlus, while Pêgas and colleagues recovered it as the sister taxon toAlbadraco, another pterosaur found in the Hațeg Basin.[16][17] Their cladograms are shown below:
Topology 1: Andres (2021). | Topology 2: Pêgas and colleagues (2023).
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While the skull ofHatzegopteryx 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 and colleagues suggested that, in order to fly, the skull weight ofHatzegopteryx 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 mm (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 ofexpanded polystyrene (which is used to manufactureStyrofoam). 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 toHatzegopteryx.[7]
As a consequence of its robust, thick-walled vertebrae, the neck ofHatzegopteryx was much stronger than that ofArambourgiania. 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) forArambourgiania andHatzegopteryx. WhileArambourgiania's neck vertebrae fail at about half of its body weight, the posterior neck vertebrae ofHatzegopteryx can withstand anywhere between five and ten body weights, depending on the loading of the bone. Even the hypothetically longer anterior neck vertebrae ofHatzegopteryx would be able to withstand four to seven body weights.[7]
Although thecentrum ofHatzegopteryx is much more robust thanArambourgiania, their ratios of bone radius to bone thickness (R/t)[8] are roughly the same (9.45 forHatzegopteryx and 9.9 forArambourgiania). This may represent a compromise between increasingbending strength andbuckling 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.[7]
In order to support the robust head, the neck ofHatzegopteryx was likely strongly muscled. On theoccipital bones, thenuchal lines, which serve as muscular attachments, are very well-developed and bear prominent scarring. These conceivably supported thetransversospinalis muscles, which aid in extension and flexion of the head and neck. Likewise, the opisthotic process,neural spines, andzygapophyses 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 ofArambourgiania probably would not have been as extensively muscled as that ofHatzegopteryx.[7]
Like all azhdarchid pterosaurs,Hatzegopteryx was probably a terrestrially foraging generalist predator.[18] It is significantly larger than any other terrestrial predator fromMaastrichtian Europe. This, due to its large size in an environment otherwise dominated byisland dwarfdinosaurs (with no large hypercarnivoroustheropods in the region) it has been suggested thatHatzegopteryx played the role of anapex predator in theHațeg Island ecosystem. The robust anatomy ofHatzegopteryx suggests that it may have tackled larger prey than other azhdarchids, including animals too large to swallow whole.[18] Meanwhile, other giant azhdarchids, likeArambourgiania, would probably have instead fed on small prey (up to the size of a human), including hatchling or small dinosaurs and eggs.[7] Another pterosaur,Thalassodromeus, has similarly been suggested to beraptorial.[19]
Apart fromHatzegopteryx, there are various other unusualdenizens of the Hațeg Island ecosystem. Co-occurringpterosaurs included the small azhdarchidEurazhdarcho, with a wingspan of 3.8 m (12 ft),[6] an unnamed, small-sized short-necked azhdarchid with a wingspan of 3.5 to 4 m (11.5 to 13.1 ft), a somewhat larger and likewise unnamed azhdarchid, with a wingspan of 5 m (16.4 ft), and apparently smallpteranodontids have been found as well.[20] The robust, flightless, and possibly herbivorousavialan[21] ordromaeosaurid[22]Balaur, which had two enlarged claws on each foot,[22] represents another highly specialized component of the fauna. The ecosystem contained a number ofinsular dwarfs, namely thetitanosaursMagyarosaurus[23] andPaludititan,[24] thehadrosauridTelmatosaurus, and theiguanodontianZalmoxes.[23] Along with thenodosauridStruthiosaurus, various small, fragmentarymaniraptorans were present, includingBradycneme,Elopteryx, andHeptasteornis.[23] Crocodilian remains, belonging to the generaAllodaposuchus,Doratodon, andAcynodon have also been found.[25] Non-archosaurian components include thekogaionidmultituberculate mammalsKogaionon,Barbatodon,Litovoi tholocephalos, andHainina,[26][27] lizards such as theteiidBicuspidon and theparamacellodidBecklesius, an unnamedmadtsoiid snake, and thelissamphibiansAlbanerpeton,Eodiscoglossus, andParadiscoglossus.[28]
The importance of this fauna is a major geological justification for the designation of the area from 2004 to 2005 asHațeg Country Dinosaurs Geopark, one of the earliest members of theEuropean Geoparks Network, and (when the designation ofUNESCO Global Geoparks was ratified in 2015) as Haţeg UNESCO Global Geopark.[29]
During theMaastrichtian, 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 km2 (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 km (120 to 190 mi).[23] Being located at 27°N,[30] 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).[31] The environment consisted of variousalluvial plains,wetlands, andrivers,[32] surrounded by woodlands dominated byferns andangiosperms.[23]Paleosols indicate a relatively dry Cretaceous climate, with an annual precipitation of less than 1,000 mm (39 in).[31]
Media related toHatzegopteryx at Wikimedia Commons
