Mistralazhdarcho

''Mistralazhdarcho'' is a genus of azhdarchid pterosaur that lived during the Campanian and Maastrichtian ages of the Late Cretaceous period in what is now France. A rich fossil site was discovered in 1992 by paleontologist Xavier Valentin at Velaux–La Bastide Neuve, in the south of France. Pterosaur fossil remains would be subsequently uncovered in the site. They were found in a layer of the Aix-en-Provence Basin at Velaux–La Bastide Neuve and consist of a partial skeleton that includes the skull. These remains would later be made the holotype specimen of the new genus and type species ''Mistralazhdarcho maggii'', named and described in 2018 by Valentin, along with paleontologists Romain Vullo, Géraldine Garcia, Pascal Godefroit, and Aude Cincotta. The generic name combines the mistral, a typical northern wind from the area, and the related genus ''Azhdarcho''. The specific name honors Jean-Pierre Maggi, the mayor of Velaux, who supported the La Bastide Neuve paleontological project.

Based on extrapolations of the size of its humerus and the wingspan of the related pterosaur '' Zhejiangopterus'', the estimated wingspan for the holotype specimen of ''Mistralazhdarcho'' sits between . However, the holotype is not fully grown. Wingspans of adult individuals are estimated to have measured between . By comparing its fossil remains to those of its relatives, ''Mistralazhdarcho'' seems to have shared the most features with the genus ''Aerotitan'' from Argentina.

''Mistralazhdarcho'' was assigned to the family Azhdarchidae by Vullo and colleagues, though a cladistic analysis was not made in its description. Later studies would include ''Mistralazhdarcho'' in their phylogenetic analyses, but its placement varies depending on the study. Within Azhdarchidae, some have recovered ''Mistralazhdarcho'' in the subfamily Azhdarchinae, while others in Quetzalcoatlinae. However, its position as the sister taxon of ''Aerotitan'' has always been consistent. Because of its size, ''Mistralazhdarcho'' most likely represents a mid-sized class of European azhdarchid, its contemporary relatives in Europe were either small or gigantic.

Discovery and naming

In 1992, a rich fossil site was discovered by French paleontologist Xavier Valentin at Velaux–La Bastide Neuve, in the south of France. Between 2009 and 2012, pterosaur remains were excavated in the site. They were subsequently reported in the scientific literature in 2015 by paleontologist Aude Cincotta and colleagues, along with numerous other non-pterosaur fossil remains.

Among the pterosaur remains is specimen MMS/VBN.09.C.001, which was discovered in a sandstone layer of the Aix-en-Provence Basin at Velaux–La Bastide Neuve. The layer dates back to the late Campanian, about 72 million years ago. Specimen MMS/VBN.09.C.001 consists of a partial skeleton with the skull. It contains the symphysis of the lower jaws (the part where they join), the atlas-axis complex of the front neck, a middle neck vertebra, the left humerus, a piece of the right humerus, the left radius, the right pteroid, the shaft of the fourth metacarpal, the proximal part of the first phalanx of the wing finger, the distal part of the same phalanx, and four bone fragments that could not be identified, which include some articular surface and two shafts. The skeleton was not found articulated but the bones were discovered on a limited surface of within the total surface of formed by the fossil layer. Therefore, it was concluded they represent a single individual, probably a subadult.

In 2018, specimen MMS/VBN.09.C.001 was made the holotype of the newly named genus and type species ''Mistralazhdarcho maggii'', named and described by Valentin, along with paleontologists Romain Vullo, Géraldine Garcia, Pascal Godefroit, and Aude Cincotta. The generic name ''Mistralazhdarcho'' is a combination of the mistral, a northern wind typical of the area of discovery, and the related pterosaur ''Azhdarcho'', the type genus of Azhdarchidae, the family to which ''Mistralazhdarcho'' belongs. The specific name ''maggii'' honors Jean-Pierre Maggi, the mayor of Velaux, for his support of the La Bastide Neuve paleontological project.

Description

''Mistralazhdarcho'' is a large pterosaur. The humerus was estimated to have had an original length of . Knowing this measurement, there are a few methods that can be used in order to estimate its wingspan. One such method involves using a formula devised by Russian paleontologist Alexander Averianov. This would indicate a wingspan of about for ''Mistralazhdarcho''. Another possible method is to extrapolate the wingspan from the known skeleton of the azhdarchid '' Zhejiangopterus'', which is more complete. This would result in a wingspan estimate of . Both estimates seem to corroborate the hypothesis that the holotype individual of ''Mistralazhdarcho'' had a wingspan of about . However, said holotype was not yet fully grown. An adult exemplar could have had an estimated wingspan measuring around .

In its description, Vullo and colleagues indicated some distinguishing traits of ''Mistralazhdarcho''. One of these was an autapomorphy, a unique derived character. The upper surface of the symphysis of the lower jaws shows a well-developed elevation on the midline in a relatively forward position of behind the mandible tip, compared to in the related pterosaur ''Alanqa''. A second trait is also a possible autapomorphy, which is that the tip of the lower jaws is somewhat curved downwards. However, this trait would only be unique to ''Mistralazhdarcho'' if the related azhdarchid ''Aerotitan'' from Argentina does not have a curved tip itself. This latter pterosaur was originally described as not having one, but Vullo and colleagues, while studying ''Mistralazhdarcho'', concluded that the original description of ''Aerotitan'' was likely mistaken and that its curved holotype did not represent the middle of the jaws but their front end.

Additionally, Vullo and colleagues gave a unique combination of traits that in themselves are not unique. The upper surface of the symphysis or fusion of the lower jaws shows elevated but blunt ridges on its edges. This symphysis has a V-shaped cross-section, thus lacking a lower crest. The underside of the atlas-axis complex of the neck is flat. In the middle neck vertebrae the front articulation processes, the prezygapophyses, lightly diverge. The humerus is relatively short compared to the radius, with 66% of its length.

In 2021, in a more thorough analysis of the already mentioned genus ''Aerotitan'', paleontologist Rodrigo Pêgas and colleagues compared its holotype to those of other azhdarchids, where they concluded that, among them, ''Mistralazhdarcho'' shared that most common features, especially its mandibular tip.

Classification

In its description in 2018, ''Mistralazhdarcho'' was placed in the family Azhdarchidae, without an exact cladistic analysis. The elevation on the symphysis shared with ''Alanqa'' suggests a close relationship between the two genera. However, later phylogenetic analyses do not corroborate their close relationship. For example, a 2021 study by American paleontologist Brian Andres recovered ''Mistralazhdarcho'' as the sister taxon of ''Aerotitan'' in the subfamily Azhdarchinae within Azhdarchidae, in the most derived (advanced) position. ''Alanqa'' in this analysis was not even recovered as an azhdarchid, but as a thalassodromid instead. The close relationship between ''Mistralazhdarcho'' and ''Aerotitan'' would later be demonstrated again in a phylogenetic analysis by Pêgas and colleagues in 2023, where they found both azhdarchids in a trichotomy with the genus ''Arambourgiania''. However, unlike Andres in 2021, Pêgas and colleagues found them nested within the subfamily Quetzalcoatlinae.

Cladogram by Andres (2021).

Cladogram by Pêgas and colleagues (2023).

Paleobiology

''Mistralazhdarcho'' is the first pterosaur named from the Campanian to the Maastrichtian of Western Europe. Due to its size, ''Mistralazhdarcho'' possibly represents an intermediate size class of European azhdarchids, in between the smaller genus ''Eurazhdarcho'' and the giant form ''Hatzegopteryx''.

References

{{Portal bar, Paleontology, France

Late Cretaceous pterosaurs of Europe
Azhdarchidae
Fossil taxa described in 2018