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Vallesaurus
Temporal range: Late Triassic, Norian
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Holotype specimen of Vallesaurus cenenis
Scientific classification
Unrecognized taxon (fix): Vallesaurus
Species

Vallesaurus is an extinct genus of Triassic reptile belonging to the family Drepanosauridae. First found in Northern Italy in 1975, it is one of the most primitive drepanosaurs. V. cenenis is the type species, named in 1991. A second species, V. zorzinensis, was named in 2010.

Nomenclature

The first specimen of Vallesaurus cenensis, MCSNB 4751, was found in 1975 by the staff of the Museo Civico di Scienze Naturali of Bergamo, Italy. The genus was named in respect of professor Valle, the former director of the museum. The species, on the other hand, was named after a local municipality called Cene neighbouring the site where the fossil was excavated. The specimen was given to palaeontologist Rupert Wild to study at the Staatliches Museum of Stuttgart, Germany. Wild named the genus in 1991.[2]

The second species, V. zorzinensis, was found in the same location and identified from the specimen MCSNB 4783. The specific name referred to the Zorzino Limestone Formation, where the holotype was found.[1]

Physical Charcteristics

Vallesaurus is a small drepanosaurid about 15 centimetres (5.9 in) long. It is pentadactyl, with the 4th digit being longest and equal in length to the humerus. Its tarsus has a centrale, or an ankle bone which articulates with the tibia. In addition, Vallesaurus also has modified distal tarsals and metatarsals, and a clawless hallux.[2]

Vallesaurus differs in some characteristics from another drepanosaur, Megalancosaurus. Vallesaurus has a proportionally shorter and higher snout, a thicker and larger maxilla and set of maxillary teeth, and a shorter cervical vertebra. It also lacks the fusion between the neural spines of the second and third dorsal vertebrae. Vallesaurus differs from Drepanosaurus, another drepanosaur, in that it lacks the enormous claw found on the second digit of the manus. It can be distinguished from Drepanosaurus, Megalancosaurus and possibly Dolabrosaurus in the lack of a terminal spine at the end of the tail. In addition, Vallesaurus also differs from Hypuronector, a related drepanosaur, in having anteroposteriorly extended neural spines of the anterior dorsal vertebrae and forelimbs much shorter than the hindlimbs.[2]

Behavioral Adaptations

Vallesaurus shares with all other known drepanosaurids a body structure[3] that indicates a specialized adaptation toward climbing, especially on narrow supports such as the twigs of trees. The manus of Vallesaurus has no opposable fingers; however, the shape and length of the fingers suggest good climbing abilities.[4]

Vallesaurus as well as other drepanosaurids possess a fussed-like structure in the anterior dorsal region and highly modified cervical vertebrae with adaptations that limited lateral mobility. Both structures indicate the presence of powerful muscles and ligaments for the extension of the neck. This possibly suggests a projectile feeding adaptation.[3] The head was suddenly launched forward to catch prey and the limited lateral mobility prevented undesired jerks of the neck which could have dislocated the cervical vertebrae during the quick extension. In smaller drepanosaurids like Megalancosaurus and Vallesaurus, such adaptations may be related to an insectivorous diet. The teeth of Vallesaurus seem well suited to cut or crush the tough exoskeleton of insects and other arthropods.[2]

References

  1. ^ a b Silvio Renesto, Justin A. Spielmann, Spencer G. Lucas, and Giorgio Tarditi Spagnoli (2010). "The taxonomy and paleobiology of the Late Triassic (Carnian-Norian: Adamanian-Apachean) drepanosaurs (Diapsida: Archosauromorpha: Drepanosauromorpha)". New Mexico Museum of Natural History and Science Bulletin. 46: 1–81. 
  2. ^ a b c d Renesto S. & Binelli G. (2006) “’’Vallesaurus Cenensis’’ Wild, 1991, A Drepanosurid (Reptilia, Diapsida): From the Late Triassic of Northern Italy”, Riv. It. Paleont. Strat. 112: 77–94, Milano.
  3. ^ a b Renesto, S. (2000) “Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of North Italy.” Riv. It. Paleont. Strat. 106: 157-180, Milano.
  4. ^ Unwin D. M., Alifanov V. R. & Benton M. J. (2000) “Enigmatic small reptiles from the Middle Triassic of Kirgizia”, pp. 177–186. In: Benton M. J., Unwin D. M. & Kurochin E. “The age of Dinosaurs in Russia and Magnolia”, Cambridge University Press, Cambridge.

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