Phosphatodraco

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Phosphatodraco
Temporal range:
Ma
Phosphatodraco vertebra - Longrich et al 2018.PNG
Assigned C5
cervical
(neck) vertebra in multiple views
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Order: Pterosauria
Suborder: Pterodactyloidea
Family: Azhdarchidae
Subfamily:
Quetzalcoatlinae
Genus: Phosphatodraco
Pereda-Suberbiola et al., 2003
Type species
Phosphatodraco mauritanicus
Pereda-Suberbiola et al., 2003

Phosphatodraco is a

Ouled Abdoun Phosphatic Basin. The specimen was made the holotype of the new genus and species Phosphatodraco mauritanicus in 2003; the genus name means "dragon from the phosphates", and the specific name refers to the region of Mauretania. Phosphatodraco was the first Late Cretaceous pterosaur known from North Africa, and the second pterosaur genus described from Morocco. It is one of the only known azhdarchids preserving a relatively complete neck, and was one of the last known pterosaurs. Additional cervical vertebrae have since been assigned to the genus, and it has been suggested that fossils of the pterosaur Tethydraco
represent wing elements of Phosphatodraco.

Due to the fragmentary nature of the holotype cervical vertebrae, there has been controversy over their order. The describers considered them as cervicals (abbreviated as C) C5–C9 in the series, the first preserved vertebra (C5) being broken in two, but others consider them C3–C8, C3 and C4 being two different vertebrae. The interpretation followed has consequences for how Phosphatodraco is distinguished from other azhdarchids and how large it is thought to have been; the describers considered it to have had a wingspan of 5 m (16 ft); the alternate interpretation would lead to a 4 m (13 ft) wingspan. The complete neck may have been 865 mm (2 ft 10 in) long. Phosphatodraco is mainly distinguished by its C8 (or C7) vertebra being very elongated, 50% longer than the C5, and in having a prominent

neural spine
that is almost as tall as the centrum (the main part of the vertebra), truncated in a square shape at the top, and located far back. As an azhdarchid, it would have had a proportionally long neck, small body, and long limbs, compared to other pterosaurs.

The closest relatives of Phosphatodraco appear to have been

Cretaceous-Paleogene extinction event
, indicates their extinction happened abruptly.

Discovery

stratigraphic
location of the discovery site, "couche III" (C)

During the late 1990s, remains of

Centre National de la Recherche Scientifique, which had taken place since 1997.[1][2]

The pterosaur material, catalogued as specimen OCP DEK/GE 111, consists of five disarticulated but closely associated cervical (neck) vertebrae and an indeterminate bone, most likely belonging to a single individual. The vertebrae are crushed and damaged, and the surface of the bone is missing in some areas, with some infilling of phosphate sediments, and the fossils have therefore not been removed from the matrix. The block containing the bones is 98 cm (39 in) long and 34 cm (13 in) wide. During mechanical preparation of the specimen fossil remains of other animals were also found in association, including of several types of fish and mosasaurs.[1]

The specimen was made the holotype of the new genus and species Phosphatodraco mauritanicus by paleontologist Xabier Pereda-Suberbiola and colleagues in 2003. The genus name derives from the words phosphate and the Latin draco, meaning "dragon from the phosphates", and the specific name refers to the region of Mauretania where the fossils were found.[1] The describers gave the etymology of Mauretania as Latin for North Africa; other sources specify it as an area stretching from Algeria to Morocco.[1][3][4] Phosphatodraco was the first Late Cretaceous pterosaur known from North Africa (and thus the first known member of the family Azhdarchidae of this age from the region), and only the second pterosaur genus described from Morocco (the first being Siroccopteryx). At the time it was described, it was one of the only known azhdarchids preserving a relatively complete neck (the others being Zhejiangopterus and Quetzalcoatlus[5]), and was one of the last known pterosaurs.[1] Complete neck vertebral series are rare for azhdarchids, but such vertebrae are some of the most commonly found and best known remains of the group.[6]

In 2018 paleontologist Nicholas R. Longrich and colleagues reported pterosaur fossils collected from "couche III" in cooperation with the

In 2020 paleontologists Claudio Labita and David M. Martill described an articulated (where the bones are connected as in life) pterosaur wing from "couche III" (specimen FSAC CP 251, bought from

pteranodontid, but Labita and Martill concluded it was an azhdarchid, and that it possibly represented the wing elements of Phosphatodraco. They noted that more associated and articulated pterosaur fossils were being collected from these deposits due to improving methods used by fossil diggers, and that azhdarchid fossils were becoming abundant. They also cautioned that the provenance of some of the Moroccan fossils was difficult to establish, due to the commercial nature of their collection.[7]

Interpretations of cervical vertebra order

Pereda-Suberbiola and colleagues originally interpreted the five preserved cervical vertebrae of Phosphatodraco as cervicals C5–C9. The frontmost preserved vertebra they interpreted as C5 consisted of two fragments; they found it unlikely that these belonged to two different vertebrae, since they lay in continuity with no sediment in between, and overlapped each other in some areas. They considered the sideways expansion at the front of this vertebra to be due to crushing, and pointed out that such preservation where fragile, yet well-preserved bones are associated with damaged material of the same individual is known from other vertebrate fossils in the same level. They identified the frontmost vertebra as a C5 because this is usually the longest cervical vertebra in pterosaurs, their length decreasing hindward.[1]

In 2007 paleontologist

axis (C2).[9][10]

Subsequent articles from 2011 and 2015 with Kellner among the co-authorship have concurred with Kellner's interpretation.[11][12] Paleontologist Alexander Averianov disagreed with Kellner's reinterpretation of the cervical vertebrae in 2014, and considered the original description accurate.[13] A 2015 article by paleontologist Mátyás Vremir and colleagues called the issue "controversial" and considered the specimen too crushed for proper comparison,[14] and Martill and Markus Moser concurred with this in 2018.[15] Paleontologists Darren Naish and Mark P. Witton (the co-authors of Vremir's article) followed Kellner's interpretation in 2017.[1][16] Paleontologist Rodrigo V. Pêgas and colleagues also followed Kellner's order in 2021.[17] Though the palaeontologist Alexandru A. Solomon and colleagues noted the suggested change in interpretation of the holotype order in 2019, they stated that even if the reinterpretation was correct, the specimen was too damaged for comparison with the single known cervical vertebra of their new genus Albadraco.[18]

Description

Estimated size (upper middle in turquoise) compared to contemporary pterosaurs
, birds, and a human

In their 2003 description, Pereda-Suberbiola and colleagues estimated Phosphatodraco to have had a wingspan close to 5 m (16 ft), based on comparison with other azhdarchids with preserved cervical vertebrae, and referred to it as a "large azhdarchid pterosaur". This is larger than azhdarchids such as Zhejiangopterus and Montanazhdarcho, and comparable to the smaller species of Quetzalcoatlus, Q. lawsoni; the larger Q. northropi is thought to have reached 10–11 metres (33–36 ft), thereby being the largest known flying animal.[1][19] Witton grouped Phosphatodraco with "midsized" azhdarchids based on this size estimate in 2013.[20] In 2010, Kellner suggested this size estimate too large, based on his reinterpretation of the neck vertebra order.[9] Naish and Witton, who followed Kellner's interpretation, listed a neck-length of 865 mm (2 ft 10 in) for Phosphatodraco in 2017, and a wingspan of 4 m (13 ft).[16]

There were two main types of azhdarchid skulls; very long, low skulls that were up to ten times longer than wide, and some that were much shorter than that, closer to those of other pterosaurs. Some had crests and some did not. Azhdarchids had necks that were proportionally longer than those of other pterosaurs, and their

pycnofibers.[21]

Cervical vertebrae

The suite of features that distinguish a taxon from other related taxa is called a diagnosis, and in the case of Phosphatodraco, these features are all found in the cervical vertebrae. Since Pereda-Suberbiola and colleagues considered the preserved vertebrae to be C5–C9 of the series in their description, that is the diagnosis and description followed here.

prezygapophyses (processes at the sides of the centrum which connected with the postzygapophyses of the previous vertebrae) of the middle cervical vertebrae is about 4.3 in C5 and 4.1 in C6.[1]

The five preserved cervical vertebrae have hollow centra and their

postexapophysial process (which connected with the preexapophys at the front of the preceding vertebra) is in front of it, all lying in the same plane due to crushing.[1]

The C6 (Kellner's C5

foramina (holes) on the side surface of the centrum. The front cotyle (the concave front end of the centrum) is distorted, but it appears to be twice as wide as high, ovoid (or egg-shaped), and with a slightly concave upper margin. The lower margin has a prominent hypapophysis (a downwards projection), and this keel's height diminishes towards the centrum's mid-length. There is a longitudinal oval sulcus (a groove) on the right side of the lower surface, near the base of the prezygapophysis. The lower surface of the centrum is nearly flat, and the postexapophys is well-developed at the lower side of the condyle, like in the preceding vertebrae.[1]

The following C7 vertebra (Kellner's C6

neural canal (through which the spinal cord passed) was located, though its features cannot be accurately determined.[1]

The next to last vertebra is C8 (Kellner's C7

neural arch (which forms the arch of bone through which the spinal cord passed). It is similar to the same vertebra of Quetzalcoatlus in that the neural spine is square on top, but differs in being placed so far back. The left postexaphophyseal process is well-developed at the back and below, but does not extend past the condyle as it does in the preceding vertebrae.[1]

The last vertebra is the C9 according to Pereda-Suberbiola and colleagues (Kellner's C8,

transverse processes (which projected from the sides of the centrum and acted as attachment points for muscles and ligaments). The neural spine terminates in a blunt process above, and the hind side of the neural spine has an oval depression, which has thick vertical edges at its sides. The transverse processes are long and slender, and project to the sides and slightly downwards. The neural canal is small and nearly circular, is about 22 mm (0.87 in) in diameter, and there are no pneumatic foramina near it. Its condyle is broad, around five times wider than high, and is crescent-shaped in cross-section. The left postexapophysis is placed at the side of the condyle and almost vertical. Though none of the vertebrae preserve cervical ribs, the development of the transverse processes of the last vertebra indicates that it probably had ribs.[1] The indeterminate bone fragment associated with the two last vertebrae has a similar texture to them, is flat and crescent-shaped, and is about 9 mm (0.35 in) wide and 44 mm (1.7 in) long.[1]

Life restoration
showing Phosphatodraco in terrestrial pose

Pereda-Suberbiola and colleagues found that the frontmost preserved cervical vertebrae of Phosphatodraco (their C5–C7) were similar in form to those of the mid-series cervical vertebrae of other long-necked

dorsal vertebrae, back vertebrae which have been incorporated into the neck. The total number of cervical vertebrae in pterosaurs varies between seven and nine, and the first dorsal vertebra is considered to be the first one that connects with the sternum (breast bone). Early pterosaurs like Rhamphorhynchus had eight cervical vertebrae with cervical ribs on at least C3–C8; later pterodactyloids had seven vertebrae and no ribs. In later pterdactyloid groups, nine cervical vertebrae are present, two of them being cervicalized dorsals, and adults have a notarium (a structure consisting of fused vertebrae in the shoulder region, also seen in birds).[1]

Classification

In their 2003 description Pereda-Suberbiola and colleagues considered Phosphatodraco a member of Azhdarchidae based on features such as its mid-series cervical vertebrae being elongated, with low

vestigial (almost evolutionarily lost) or absent neural spines, the presence of prezygapophyseal tubercles, a pair of lower sulci near the prezygapophyses, and the lack of oval pneumatic foramina on the lower surfaces of the centra. These features are especially similar to those of Quetzalcoatlus and Azhdarcho. Other features distinguishing the group could not be identified in Phosphatodraco due to the preservation of its fossils.[1]

Longrich and colleagues performed a

synapomorphy (a distinct, ancestrally shared feature), that the side margin of the mid-cervical vertebrae is straight when viewed from above and below, with almost parallel sides. These researchers noted that previous studies had defined Azhdarchidae as a node-based clade with Azhdarcho and Quetzalcoatlus as internal specifiers, but cautioned that in their new phylogeny, Phosphatodraco, Zhejiangopterus, and Eurazhdarcho would fall outside the group. They found this undesirable, as those genera had otherwise consistently been considered azhdarchids, and that for stability's sake, Phosphatodraco should be added as a third internal specifier for the group, since this would result in all these taxa being included.[17]

In 2021 paleontologist Brian Andres and colleagues also found Phosphatodraco and Aralazhdarcho to be sister taxa, supported by the reduction of pneumatic foramina on the side of the neural canal. This clade was recovered as part of the azhdarchid subclade Quetzalcoatlinae. The

Azhdarchiformes according to Andres and colleagues, 2021:[22]

Azhdarchiformes

Radiodactylus langstoni

Montanazhdarcho minor

Azhdarchidae
Azhdarchinae

Azhdarcho lancicollis

Albadraco tharmisensis

Aerotitan sudamericanus

Mistralazhdarcho maggii

Quetzalcoatlinae

Aralazhdarcho bostobensis

Phosphatodraco mauritanicus

Eurazhdarcho langendorfensis

Zhejiangopterus linhaiensis

Cryodrakon boreas

Wellnhopterus brevirostris

Hatzegopteryx thambema

Arambourgiania philadelphiae

Quetzalcoatlus lawsoni

Quetzalcoatlus northropi

Paleobiology

Feeding and ecological niche

In 2008 Witton and Naish pointed out that although azhdarchids have historically been considered to have been

piscivores (fish-eaters), and despite their unusual anatomy, azhdarchids have been assumed to have occupied the same ecological niche. Witton and Naish noted that evidence for this mode of feeding lacked support from azhdarchid anatomy and functional morphology; they lacked cranial features such as sideways compressed lower jaws and the shock-absorbing adaptations required, and their jaws instead appear to have been almost triangular in cross-section, unlike those of skim-feeders and probers.[6]

Witton and Naish instead stated that azhdarchids probably inhabited inland environments, based on the taphonomic contexts their fossils have been found in (more than half the fossils surveyed were from for example

Witton elaborated in a 2013 book that the proportions of azhdarchids would have been consistent with them striding through vegetated areas with their long limbs, and their downturned skull and jaws reaching the ground. Their long, stiffened necks would be an advantage as it would help lowering and raising the head and give it a vantage point when searching for prey, and enable them to grab small animals and fruit.[23] In their 2021 study that reinterpreted Tethydraco as an azhdarchid, and possibly the same as Phosphatodraco, Labita and Martill noted that azhdarchids might have been less terrestrial than suggested by Witton and Naish, since the Moroccan fossils were from marine strata, as was Arambourgiania from the phosphates of Jordan. They noted that no azhdarchids had been found in truly terrestrial strata, and proposed they could instead have been associated with aquatic environments, such as rivers, lakes, marine and off-shore settings.[7]

Pterosaurs are generally thought to have gone gradually

Early Cenozoic.[2]

Locomotion

Witton summarized ideas about azhdarchid flight abilities in 2013, and noted they had generally been considered adapted for soaring, although some have found it possible their musculature allowed flapping flight like in swans and geese. Their short and potentially broad wings may have been suited for flying in terrestrial environments, as this is similar to some large, terrestrially soaring birds. Albatross-like soaring has also been suggested, but Witton thought this unlikely due to the supposed terrestrial bias of their fossils and adaptations for foraging on the ground. Studies of azhdarchid flight abilities indicate they would have been able to fly for long and probably fast (especially if they had an adequate amount of fat and muscle as nourishment), so that geographical barriers would not present obstacles.[24]

Azhdarchids are also the only group of pterosaurs to which trackways have been assigned, such as Haenamichnus from Korea, which matches this group in shape, age, and size. One long trackway of this kind shows that azhdarchids walked with their limbs held directly underneath their body, and along with the morphology of their feet indicates they were more proficient on the ground than other pterosaurs. According to Witton, their proportions indicate they were not good swimmers on the other hand, and though they could probably launch from water, they were not as good at this as some other pterosaur groups.[24]

Paleoenvironment

Phosphatodraco is known from the "couche III" phosphatic unit of the Ouled Abdoun Basin in Morocco, which was deposited during the late Maastrichtian age of the Late Cretaceous period, which ended 66 million years ago. The phosphatic series is condensed and the Maastrichtian part is only 3–5 cm (1.2–2.0 in) thick. From the bottom to the top, "couche III" consists of thin phosphatic levels and

Tethys Sea at the time.[2]

The phosphatic matrix of the original Phosphatodraco specimen is gray and mottled with orange, and contained fossils including of the fish

sauropod fossils are also known. Longrich and colleagues suggested in 2018 that, although the fauna was overwhelmingly marine, the presence of terrestrial dinosaurs and azhdarchids indicates the coast was nearby.[2][7][25][27]

See also

References

Bibliography