Tethydraco

Summary

Tethydraco
Temporal range: Late Cretaceous, 66 Ma
Tethydraco humerus.PNG
Holotype humerus
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Order: Pterosauria
Suborder: Pterodactyloidea
Family: Pteranodontidae
Genus: Tethydraco
Longrich et al., 2018
Type species
Tethydraco regalis
Longrich et al., 2018

Tethydraco is a genus of pterodactyloid pterosaur, during the Late Cretaceous living in the area of present Morocco. The type species is Tethydraco regalis.[1]

Discovery and naming

Maps showing phosphate mines in Morocco where the fossils were found

Since 2015, a group of paleontologists is acquiring pterosaur fossils from commercial Moroccan fossil traders, who obtain these from workers in the phosphate mines on the Khouribga plateau, which is located within the Ouled Abdoun Basin. The purpose of this project is to determine pterosaur diversity in the latest Cretaceous. From this stage, no Konservat-Lagerstätten are known, sites combining a large variety of species with exceptional preservation. It is in such sites that the vast majority of pterosaur fossils and taxa have been discovered. The latest Cretaceous had only produced some partial skeletons of Azhdarchidae. Researchers usually have concluded from this fact that other pterosaur groups had already gone extinct. However, an alternative explanation could be that the poor fossil record caused a distorted image of the true situation through undersampling. To test this hypothesis, it was tried to collect all pterosaurs bones brought to light by the massive and systematic commercial exploitation of the Khourigba phosphate layers. It transpired that indeed some finds could not be determined as azhdarchids and likely represented other groups. It was decided to publish four of these as new species.[1]

In 2018, Nicholas R. Longrich, David M. Martill and Brian Andres described and named the type species Tethydraco regalis. The generic name combines a reference to the Tethys, the ocean in the Late Cretaceous separating Africa from Europe and Asia, with a Latin draco, "dragon". The specific name means "royal" in Latin.[1]

The holotype, FSAC-OB 1, was found in the middle Couche III, itself the lowest phosphate layer complex at Sidi Daoui, dating from the late Maastrichtian. It consists of a left humerus. The bone is relatively crushed. Other specimens have been referred to the species. FSAC-OB 199 is an ulna. FSAC-OB 200 is another ulna. FSAC-OB 201 is a thighbone. FSAC-OB 202 consists of a thighbone with shinbone. The describing authors admitted that a connection between the holotype and the referred specimens is hard to proof, in view of the lack of overlapping material. However, the wide ulnae fit the exceptional distal width of the humerus. The thighbones were, more tentatively, referred because they seemed to be pteradontid.[1]

Description

Size (blue, middle left) compared to other pterosaurs, birds, and a human

The wingspan of Tethydraco has been estimated at five metres.[1]

The describing authors indicated some traits in which Tethydraco could be distinguished from known pteranodontids. In the humerus, the deltopectoral crest is placed rather proximally, closer to the torso of the animal, its closest border being positioned just proximal to the beginning of the opposite crest, the crista ulnaris. Distally, away from the torso, the humerus has a broad triangular expansion. The bone ridge running to the outer joint condyle has a distinct process pointing to above, when the wing is in a stretched position. The ridge leading to the inner condyle is enlarged and extends towards the torso over a long distance. The ulna is relatively short and wide while its proximal end, towards the humerus, is massively expanded.[1]

Phylogeny

Referred hindlimb elements

Tethydraco was placed in the Pteranodontidae. A cladistic analysis recovered it as the sister species of a clade consisting of Pteranodon and Geosternbergia (= Pteranodon sternbergi). It would then be the youngest known pteranodontid. Its existence was seen as proof that pterosaur diversity in the Maastrichtian was higher than previously assumed. Pterosaur decline was an illusion caused by the Signor–Lipps effect, groups seeming to disappear earlier than a mass extinction because their youngest fossils by chance have been found at somewhat older layers than the extinction event.[1]

Below is a cladogram showing the results of a phylogenetic analysis first presented by Andres et al. in 2014, and updated with additional data by Andres and colleagues in 2018.[2]

Ornithocheiroidea

Azhdarchoidea

 Pteranodontoidea 

Ornithocheiromorpha

 Pteranodontia 
Pteranodontidae

Pteranodon sternbergi

Pteranodon longiceps

Tethydraco regalis

Nyctosauridae

Alamodactylus byrdi

Volgadraco bogolubovi

Cretornis hlavaci

Alcione elainus

Simurghia robusta

Muzquizopteryx coahuilensis

Barbaridactylus grandis

Nyctosaurus lamegoi

Nyctosaurus nanus

Nyctosaurus gracilis

Paleoecology

Tethydraco was discovered in the Ouled Abdoun Basin in Morocco. This basin is divided into layers called "Couches," and Tethydraco was discovered in Couche III. It coexisted with the pterosaurs Alcione, Barbaridactylus, Simurghia and Phosphatodraco and the abelisaurid dinosaur Chenanisaurus.[1][3]

References

  1. ^ a b c d e f g h Longrich, Nicholas R.; Martill, David M.; Andres, Brian; Penny, David (2018). "Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary". PLOS Biology. 16 (3): e2001663. doi:10.1371/journal.pbio.2001663. PMC 5849296. PMID 29534059.
  2. ^ Andres, B.; Clark, J.; Xu, X. (2014). "The Earliest Pterodactyloid and the Origin of the Group". Current Biology. 24 (9): 1011–6. doi:10.1016/j.cub.2014.03.030. PMID 24768054.
  3. ^ Longrich, N.R.; Pereda-Suberbiola, X.; Jalil, N.-E.; Khaldoune, F.; Jourani, E. (2017). "An abelisaurid from the latest Cretaceous (late Maastrichtian) of Morocco, North Africa". Cretaceous Research. 76: 40–52. doi:10.1016/j.cretres.2017.03.021.