Arcticodactylus (lat.) - a genus of basal pterosaurs that lived in the Triassic period on the territory of modern Greenland . The only species of Arcticodactylus cromptonellus was previously assigned to the genus Eudimorphodon , and its closest relatives may have been Eudimorphodon or Austriadraco .
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Arcticodactylus Kellner, 2015 | |||||||||||||||||||||||||||||||||||||||||
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† Arcticodactylus cromptonellus
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| Geochronology Norian Age 227—208.5 Ma
◄ Nowadays◄ Cretaceous-Paleogene extinction◄ Triassic extinction◄ Mass Permian Extinction◄ Devonian extinction◄ Ordovician-Silurian extinction◄ Cambrian explosion | |||||||||||||||||||||||||||||||||||||||||
In 1989, William Amaral discovered a rich site with fossils on Mount McKnight in eastern Greenland, which was excavated in 1991 and 1992. The skeleton of a small pterosaur became part of the extracted material. In 2001, , Neal Shubin , Stephen Gates and named and described it as a new species of Eudimorphodon cromptonellus . The species name was given in honor of Professor Walter Crompton, and the Latin suffix -ellus means a decrease, and in this case indicates a small sample size [2] .
The holotype MGUH VP 3393 was found in the Carlsberg Fjord Beds field of the Ørsted Dal group of the formation, which dates back to the Norian – Rat centuries of the Triassic. The holotype is an incomplete skeleton with a skull, largely dissected [2] .
The assignment of the remains to Eudimorphodon was based mainly on the similarity of the shape of the teeth, especially on the distinctive structure of the tooth with three, four and five crown tops. In 2003, noted that other basal pterosaurs also had such teeth [3] . In 2014, Fabio Marco Dalla Vecchia noted that Eudimorphodon cromptonellus does not share a single trait with E. ranzii , which other pterosaurs do not have, except for the absence of distinctive fang-shaped teeth, pterygoid teeth and striated tooth enamel [4] . In 2015, Kellner singled out a separate genus, Arcticodactylus . The genus name consists of the name of the Arctic with the addition of other Greek. δάκτυλος - “finger”. The type species became Arcticodactylus cromptonellus [5] .
An individual whose remains served as a holotype was, in 2001, the smallest pterosaur of all known: it is estimated that the wingspan of this animal was 24 centimeters. Histological examination of the bone structure showed that the individual was not an adult, but was not a chick [2] .
In 2015, Kellner established some distinctive features that correct and supplement the 2001 findings. The jaws had eleven or twelve teeth on each side. The joint surface of the fourth metacarpal bone with the fourth finger shows two true condyles. The femur is only slightly shorter than the tibia : 96% of its length. The shoulder blade is much larger than a coracoid . The humerus is only slightly shorter than the femur, 92% of its length, or 91% of the length of the ulna . The femur is slightly longer than the first phalanx of the wing of the finger, which is 91% of the length of the femur. The third metatarsal bone of the foot is elongated and equal to 56% of the length of the tibia. These proportions mean that Arcticodactylus had relatively short wings and large legs [5] .
Among other things, Arcticodactylus should be distinguished from Eudimorphodon due to the absence of long fang-shaped teeth in the middle of the dentition, and from Eudimorphodon ranzii , Carniadactylus and Bergamodactylus due to a triangular instead of a rectangular deltopectoral crest on the humerus. Articodactylus had fewer teeth than any other known Triassic pterosaurus [5] .
Jenkins and colleagues argued that the unique type of articulation of the main metacarpal wing with a long finger, using two rounded condyles, was a transition state between the ancestral form, which had one articulated surface of the metacarpal bone, allowing it to move sideways, and a more advanced form of articulation late pterosaurs. Two condyles, of which the upper one was larger, would force the finger to move in the optimal plane when the wing was raised upward [2] .
In 2001, E. cromptonellus was assigned to the family Eudimorphodontidae [2] . Kellner in 2015 indicated a basal position within the pterosaur squad. The presence of a short coracoid suggested a close proximity to Austriadraco within Austriadraconidae . According to Kellner, the authors of the initial description incorrectly identified the coracoid as a square bone [5] .
Notes
- ↑ † Arcticodactylus cromptonellus information on the Fossilworks website. (Retrieved November 26, 2016) .
- ↑ 1 2 3 4 5 Jenkins, FA Jr., Shubin, NH, Gatesy, SM, Padian, K. A diminutive pterosaur (Pterosauria: Eudimorphodontidae) from the Greenlandic Triassic (English) // Bulletin of the Museum of Comparative Zoology. - 2001. - Vol. 156 . - P. 151-170 .
- ↑ Kellner, AWA Pterosaur phylogeny and comments on the evolutionary history of the group // Evolution and Palaeobiology of Pterosaurs / Buffetaut E., Mazin JM. (Eds). - London: Geological Society of London, Special Publications, 2003 .-- P. 105-137. - 347 p.
- ↑ Dalla Vecchia FM Gli pterosauri triassici. - Udine: Memorie del Museo Friulano di Storia Naturale, pubblicazione numero 54, 2014 .-- 319 p., 266 figs p.
- ↑ 1 2 3 4 Kellner, Alexander WA Comments on Triassic pterosaurs with discussion about ontogeny and description of new taxa (English) // Anais da Academia Brasileira de Ciências. - 2015. - Vol. 87 , no. 2 . - P. 669-689 .