| Cryodrakon | |
|---|---|
 | |
| Theholotype specimen consists of a wingbone (upper left), a fourth neck vertebra (middle top), a left humerus (upper right), and a tibia (bottom) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Pterosauria |
| Suborder: | †Pterodactyloidea |
| Clade: | †Azhdarchoidea |
| Family: | †Azhdarchidae |
| Subfamily: | †Quetzalcoatlinae |
| Genus: | †Cryodrakon Hone et al.,2019 |
| Species: | †C. boreas |
| Binomial name | |
| †Cryodrakon boreas Hone et al., 2019 | |
Cryodrakon is agenus ofazhdarchidpterosaur that lived during the lateCampanian age of theLate Cretaceous period in what is nowCanada, around 76.7 and 74.3 million years ago. Starting in 1972, fossil remains of large azhdarchid pterosaurs have been reported fromAlberta.Paleontologists assigned them to the genusQuetzalcoatlus, given that it was the only known azhdarchid from North America back then and because they had limited information about its actual remains, so they simply could not deduce anything different. In 1992, a partial pterosaur skeleton was uncovered in theDinosaur Park Formation of Alberta. It was partially described in 1995 by paleontologistPhilip J. Currie and colleagues, with a subsequent and more complete description in 2005. But it was not until 2019 that it received a newgenus andtype species,Cryodrakon boreas, named and described by paleontologists David Hone, Michael Habib, and François Therrien. The partial skeleton was made theholotype specimen of this new pterosaur. Its generic name means "cold dragon" inAncient Greek, in reference to its Canadian origin, while itsspecific name refers to the Greek god of the north winds,Boreas. All azhdarchid remains from the Dinosaur Park Formation were subsequently referred toCryodrakon.
Most of the fossil remains ofCryodrakon belong to either young or subadult individuals, from which awingspan of about 5 m (16 ft) could be estimated. However, much larger fossils have been unearthed, including an incomplete fifthcervical (neck) vertebra that measures 40 cm (1 ft 4 in). If complete, it could have measured at least 50 cm (1 ft 8 in). Adult individuals ofCryodrakon would have had a similar size toQuetzalcoatlus northropi based on the size of its fossils. A wingspan of about 10 m (33 ft) is the most commonly estimated forCryodrakon, which makes it one of thelargest flying animals to ever exist.
In its description,Cryodrakon was assigned to family Azhdarchidae, which includes the already mentionedQuetzalcoatlus. Aphylogenetic analysis was not performed due to the fragmentary nature of its remains, but the describers pointed out certain features that would excludeCryodrakon from being in a basal (primitive) position within Azhdarchidae. Subsequent phylogenetic analyses would place it within the subfamily Quetzalcoatlinae, though in varying position depending on the study.Cryodrakon would have coexisted with many different types ofdinosaurs in the Dinosaur Park Formation, as demonstrated by the abundance of dinosaur fossils found there.
The generic nameCryodrakon is derived from theAncient Greek words κρύος (kryos, meaning "cold") and δράκων (drakon, meaning "dragon"), while thespecific nameboreas refers to the Greek god the north wind,Boreas. Hence,Cryodrakon boreas could be translated as "cold dragon of the north winds".[1] Habib had previously considered the nameCryodrakonviserion, as a reference to the ice dragon inGame of Thrones.[2]
Since 1972, bones of largepterosaurs (flying reptiles) belonging to the familyAzhdarchidae have been reported fromAlberta. These were the first pterosaur fossils discovered in Canada.[3][1][2][4] They were sometimes referred to asQuetzalcoatlus sp., indicating an uncertain species ofQuetzalcoatlus, or were just assigned toQuetzalcoatlus without specifying anything.[5][1][4] During the late 20th centuryPaleontologists who uncovered largeCretaceous azhdarchid remains in North America would provisionally assign them toQuetzalcoatlus, due to it being the only known azhdarchid from North America at the time and information about its anatomy being limited. Later research by American paleontologist Michael Habib would indicate that these fossil remains represented ataxon that was new to science.[2]
In 1992, a partial pterosaur skeleton was found and excavated inUpper Cretaceous strata ofDinosaur Provincial Park in Alberta, more precisely in a layer of theDinosaur Park Formation that dated back to the lateCampanian (between 76.7 and 74.3 million years ago). The excavation site was located near the lower or older boundary of this range. It was subsequently reported and partially described by multiple paleontologists, including Canadian paleontologistPhilip J. Currie, in 1995. They noticed that the bones had tooth marks and even a broken tip of a tooth imbedded in one of them, most likely coming fromSaurornitholestes langstoni of the same formation.[6][2][1] The bones of the skeleton were not articulated, but associated, representing an immature animal. This is the only pterosaur found in Canada with fossil remains that consist of more than just a single bone so far. Due to the skeleton's initial description only being partial, a more detailed description of was made in 2005 by Currie and Eva Koppelhus.[7][1] This partial skeleton, specimen TMP 1992.83, lacks the skull and consists of a fourthcervical (neck) vertebra, arib, ahumerus, a pteroid (wing) bone, afourth metacarpal, atibia and ametatarsal.[2][1]
In 2019, specimen TMP 1992.83 received a new separategenus andtype species,Cryodrakon boreas, and became theholotype of this new pterosaur.Cryodrakon boreas was named and described by paleontologists David Hone, François Therrien, and Michael Habib.[1]
Through comparisons with other azhdarchid taxa, Hone and colleagues concluded that all azhdarchid material from Alberta could be referred to a single distinct taxon. Therefore, they assigned all the known azhdarchid remains from the Dinosaur Park Formation toCryodrakon boreas. The specimens consisted of numerous cervical vertebrae, ascapulocoracoid, anulna, several fourth metacarpals, wing fingerphalanges and afemur. These bones represent individuals of various biological ages, among them juveniles and a large mature exemplar. However, most of the bones are from medium-sized individuals. In their 2019 study, only the cervical vertebrae were described in detail, since bones from other parts of the body had already been treated in 2005.[1][2]
The majority of the fossil remains ofCryodrakon, among them its holotype bones, most likely represented young and subadult individuals. Their dimensions are similar to those ofQuetzalcoatlus sp. (now known as the speciesQ. lawsoni[8]). Awingspan of at least 5 m (16 ft) has been set forCryodrakon based on these smaller remains.[1][4][2]Q. lawsoni is estimated to have had a similar wingspan of around 4.5 to 5 m (15 to 16 ft).[8][9] However, the remaining azhdarchid material from the Dinosaur Park Formation that was assigned toCryodrakon by Hone and colleagues indicates many individuals of varying size, from specimens less than half the size ofQ. lawsoni to others than double it. For example, specimen TMP 1996.12.369, a fifth cervical vertebra with a length of only 10.6 mm (0.42 in), is from a juvenileCryodrakon, which was given an estimated wingspan of about 2 m (6 ft 7 in). At the same time, specimen TMP 1980.16.1367 is an incomplete fifth neck vertebra with a preserved length of 40 cm (1 ft 4 in), which is estimated to have been at least 50 cm (1 ft 8 in) if complete. It presumably belonged to an adult individual.[1] This specimen was originally described in 1982 by Currie andDale Russell. They assigned it toQuetzalcoatlus northropi and mistakenly identified it as a femur. A wingspan of 13 m (43 ft) was estimated.[5][1] However, nowadays, wingspan estimates forQ. northropi have been more moderate, at around 10 to 11 m (33 to 36 ft), which would still make it one of thelargest flying animals to ever exist.[10][11]
A fully-grownCryodrakon would have most likely been of similar size toQ. northropi, based on the size of its remains. A wingspan of about 10 m (33 ft) has been estimated for adult individuals.[4][2] In his 2022 book about pterosaurs, American paleontologistGregory S. Paul had also set the same wingspan measurement forCryodrakon. This would make it one of the largest known flying animals as well.[9] The previously mentioned specimen TMP 1980.16.1367 ofCryodrakon is also comparable in size to the holotype ofArambourgiania, which measured around 60 cm (1 ft 11.62 in), indicating thatCryodrakon would have also been of similar size to this pterosaur.[1] Initial wingspan estimates ofArambourgiania ranged from 11 to 13 m (36 to 43 ft),[12][13] but more recent estimates have been more moderate, ranging from 8 to 10 m (26 to 33 ft), mostly due to the fragmentary nature of its remains. This wouldArambourgiania equal to or even slightly smaller in size thanCryodrakon.[9][14]
In terms of body structure,Cryodrakon was proportionally similar toQuetzalcoatlus and other long-necked advanced members of the Azhdarchidae, though its somewhat more robust bones may indicate that it was slightly heavier.[1]
Cryodrakon is distinguished from all other known azhdarchids by two features of its neck vertebrae. The lateral pneumatic fossae or pneumatophores, a pair of small openings leading to air pockets on either side of the neural canal, were positioned near the lower edge of theneural canal, while those of other azhdarchids (with the purported exception ofEurazhdarcho) were positioned higher up. The second distinguishing feature related to itspostexapophyses, large bony knobs adjacent to the protruding rear connection surface of each vertebra, the cotyle. The postexapophyses ofCryodrakon were prominent in width but short in length, clearly separated from thecotyle, and their facets were directed downwards.[1]
In its description, Hone and colleagues placedCryodrakon in the family Azhdarchidae. No exactcladistic analysis had been given to clarify its precise relationship with other azhdarchids. However, the describers were confident that it did not belong in thebasalmost (most primitive) position within Azhdarchidae due to the lack of distinct cervicalzygapophyses in its middle cervicals. Additionally, based on the geological age of its fossil remains,Cryodrakon would have been one of the oldest known North American azhdarchids.[1] In 2021, American paleontologist Brian Andres performed aphylogenetic analysis onQuetzalcoatlus, in which he includedCryodrakon. He recoveredCryodrakon in a derived (advanced) position in the subfamily Quetzalcoatlinae within Azhdarchidae.Cryodrakon formed a trichotomy withWellnhopterus and aclade containing the quetzalcoatlinesHatzegopteryx,Arambourgiania, andQuetzalcoatlus. His analysis is shown in the firstcladogram below.[15] In 2023, a study by paleontologist Rodrigo Pêgas et al. also recoveredCryodrakon within Quetzalcoatlinae, but differed from Andres in its specific position within the subfamily. In their analysis, they foundCryodrakon as the basalmost member of Quetzalcoatlinae. Their study is shown in the second cladogram below.[16]
Topology 1: Andres (2021). | Topology 2: Pêgas et al. (2023).
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Cryodrakon is thought to have been capable of flight,[2] which would make it one of the largest flying animals known to have existed, just likeQuetzalcoatlus.[4] Azhdarchid pterosaurs similar toCryodrakon are currently thought to have fed by hunting for smaller animals while on the ground, similar to modern daymarabou storks.[17]
Some specimens ofCryodrakon show signs of being eaten by other archosaurs, either due to predation or scavenging. The holotype partial skeleton ofCryodrakon was found to have been scavenged by a dromaeosaurid, possiblySaurornitholestes langstoni. Aside from tooth marks, a broken tooth was found in one of the bones, which, according to the authors, meant that the thin-walled bone ofCryodrakon "must have been very tough."[6][2] In 2025, a fifth cervical vertebra of a juvenileCryodrakon (TMP 2023.012.0237) showed probable crocodilian bite marks.[18]
The Dinosaur Park Formation, where fossils ofCryodrakon have been excavated, preserves many fossils from alluvial and coastal plain environments. Both of these environments would have experienced high precipitation, warm temperatures, and high humidity, with conditions becoming more swamp-like as time progressed.[19] There was a great diversity of herbivorous dinosaurs including bothlambeosaurine andsaurolophine hadrosaurs,centrosaurine andchasmosaurine ceratopsians, andnodosaurid andankylosaurid ankylosaurs, which could have been able to feed on different vegetation levels from one another.[7][20] The predatory niches were occupied by smallmaniraptorantheropods (includingdromaeosaurids andtroodontids), medium-sized juveniletyrannosaurids, and fully grown tyrannosaurids.[21]
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