| Arcticodactylus | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | †Pterosauria |
| Family: | †Eudimorphodontidae |
| Genus: | †Arcticodactylus Kellner, 2015 |
| Species: | †A. cromptonellus |
| Binomial name | |
| †Arcticodactylus cromptonellus (Jenkinset al., 2001) | |
| Synonyms | |
| |
Arcticodactylus is a genus of basalpterosaur living during theLate Triassic in the area of present-dayGreenland. Its only species was previously attributed toEudimorphodon, and its closest relatives may have beenEudimorphodon orAustriadraco.
In 1989,William Amaral on theMcKnight Bjerg in the east of Greenland discovered a rich fossil site. It was excavated in 1991 and 1992. Part of the material was a small skeleton of a pterosaur. In 2001,Farish Jenkins,Neil Shubin,Stephen Gatesy andKevin Padian named and described it as a new species ofEudimorphodon:Eudimorphodon cromptonellus. Thespecific name honors ProfessorAlfred Walter Crompton. The suffix~ellus, inLatin indicating a diminutive, alluded to the small size of the specimen.[1]
Theholotype,MGUH VP 3393, was found in theCarlsberg Fjord Beds of theØrsted Dal Member of theFleming Fjord Formation dating from theNorian –Rhaetian. It consists of a partial skeleton with skull. It is largely disarticulated.[1]
The reference toEudimorphodon had been essentially based on the similarity in tooth form, especially the distinctive multi-cuspid build with three, four or five points on the crown. In 2003,Alexander Kellner pointed out that other basal pterosaurs also possess such teeth.[2] In 2014,Fabio Marco Dalla Vecchia noted thatE. cromptonellus shared not a single trait withEudimorphodon ranzii not present in other pterosaurs but lacked the distinguishing fang-like teeth, pterygoid teeth and striated tooth enamel.[3] In 2015, Kellner named a separate genusArcticodactylus. The generic name is derived from theArctic, and Greek δάκτυλος,daktylos, "finger", a usual suffix in pterosaur names sincePterodactylus. TheLife Science Identifier is 72AE012A-018A-4B4B-950F-3CCB4C1D2471. Thetype species isEudimorphodon cromptonellus, thecombinatio nova isArcticodactylus cromptonellus.[4]
The holotype individual ofArcticodactylus is the smallest pterosaur known, with an estimatedwingspan of just 24 centimeters (9.4 in). In 2001, on the basis ofhistological research on its bone structure, it was considered not to have been fully grown yet, though not newly born.[1]
In 2015, Kellner established some distinguishing traits, correcting and adding to the 2001 diagnosis. The jaws have eleven or twelve multi-cusped teeth per side. The articulation surface of the fourthmetacarpal with the fourth finger shows two true condyles. The thighbone is only a little shorter than the shinbone, with 96% of its length. The scapula is much longer, 93%, than thecoracoid. The humerus is only slightly shorter than the thighbone, with 92% of its length, or the ulna with 91% of ulnar length. The thighbone is somewhat longer than the first phalanx of the wing finger that has 91% of femoral length. The thirdmetatarsal of the foot is elongated with 56% of shinbone length. These proportions imply thatArcticodactylus had relatively short wings and large feet.[4]
Arcticodactylus can furthermore be distinguished fromEudimorphodon in the lack of long fang-like teeth in the middle of the tooth row and fromEudimorphodon ranzii,Carniadactylus andBergamodactylus by a triangular instead of rectangular deltopectoral crest on the humerus.Articodactylus has fewer teeth than any other known Triassic pterosaur.[4]
Jenkins e.a. claimed that the unique articulation inArcticodactylus between the main wing metacarpal and the wing finger, with two rounded condyles, was a transitional shape between the ancestral form that featured a single rounded articulation surface on the metacarpal allowing a considerable amount of lateral movement, and the condition in later pterosaurs that showed a gentle depression or trochlea. The two condyles, the upper one being the largest, would have forced the finger into the most optimal plane of movement during the upstroke of the wing.[1]
In 2001,E. cromptonellus was placed in theEudimorphodontidae.[1] Kellner in 2015 indicated a basal position in thePterosauria, the short coracoid suggesting a close affinity toAustriadraco within anAustriadraconidae. According to Kellner, the original describers had incorrectly identified a coracoid as aquadrate bone.[4] The following phylogenetic analysis follows the topology of Upchurchet al. (2015).[5]
In 2020 however, a study upheld by Matthew G. Baron about early pterosaur interrelationships foundArcticodactylus to group withCarniadactylus,Raeticodactylus, and the Austriadraconidae, which in turn were within a clade he calledCaviramidae.[6]
