| Albertonykus | |
|---|---|
 | |
| Life restoration | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Alvarezsauridae |
| Genus: | †Albertonykus Longrich &Currie, 2009 |
| Species: | †A. borealis |
| Binomial name | |
| †Albertonykus borealis Longrich &Currie, 2009 | |
Albertonykus (meaning "Alberta claw") is an extinct genus ofalvarezsauriddinosaur from theMaastrichtian-age (Upper Cretaceous) rocks of theHorseshoe Canyon Formation of Alberta,Canada. It is known from forelimb and hindlimb remains from multiple individuals. All but two of the specimens come from abonebed dominated byAlbertosaurus, located at the top of Unit 4 of the Horseshoe Canyon Formation,[1] dating to ~68.5 million years ago.[2]
Albertonykus is interpreted as having fed on wood-nestingtermites because the forelimbs appear specialized for digging but are too short for burrowing.Albertonykus is the earliest knownNorth American alvarezsaurid. Isolated bones of alvarezsaurids are known from late Maastrichtian rocks inMontana andWyoming (USA). The bones now belonged to a new genus,Trierarchuncus.[3][4]
Thetype species isA. borealis, described by Nick Longrich andPhillip Currie in 2009. The specific name (borealis) means "north".[5]
Until the 1990s it was unknown that dinosaurs likeAlbertonykus existed. A chain of new discoveries from Asia and South America exposed the existence of these previously unknown theropod dinosaurs.[6] North American finds remained rare. The bones ofAlbertonykus were discovered through a coincidental association with a much larger theropod dinosaur. In 1910,paleontologistBarnum Brown and his crew found a site filled with the bones of the gigantictyrannosauridAlbertosaurus sarcophagus. They unearthed the remains of at least nine different specimens ofAlbertosaurus in the single site, but stopped digging after just two weeks.[7]
Renewed quarrying in theAlbertosaurus bonebed in Dry Island Provincial Park again produced the remains of over twenty specimens ofAlbertosaurus, and the quarry has yet to be fully excavated. It is not known why so many tyrannosaurs were found in one place: paleontologist Nick Longrich speculated that the site was part of apredator trap, where trapped prey animals drew predators to their deaths.[7]
At the same site, over a dozen arm and leg bones belonging to an unknown species of small theropod were in 2002 excavated by a team of scientist led byPhilip John Currie of theUniversity of Alberta. The bones were then stored at theRoyal Tyrrell Museum in Alberta.[8][9] In 2005 Nick Longrich, then a student at theUniversity of Calgary, happened upon the small fossils while comparingAlbertosaurus claws to other dinosaur species. Longrich recognized the fossils as alvarezsaurid, concluding that they represented a new species.[8][9] Other fragments ofAlbertonykus were then recognized in the collections, which had not been identified as a separate species.[6]
Albertonykus is the smallest knownalvarezsauridae ever discovered in North America, measuring 1.1 m (3.6 ft) long and weighing 5 kg (11 lb).[10] Alvarezsaurs typically had slender hind legs, long rigid tails, and unusually short arms that were powerfully built to support a large claw. Although no skull bones ofAlbertonykus have been found, related animals fromMongolia show that they likely had long, slender snouts filled with tiny teeth similar to those of armadillos and anteaters.[7] It is likely thatAlbertonykus ate insects, using its large thumb claw to tear open rotten logs to find its prey.[8] As in other alvarezsaurs, the forelimbs ofAlbertonykus were specialized for digging, but were too short to permit burrowing. Unfortunately, at this time the skeleton ofAlbertonykus is not complete, but its Mongolian relatives give us a distinct idea of what the rest of the skeleton would have looked like.[7]
Possible prey items were evaluated and compared with the fossil record of social insects.Ants were not an important part of the ecosystem during the Cretaceous, and mound-building termites do not appear until the Eocene. This leaves the possibility thatAlbertonykus preyed on wood-nesting termites. This hypothesis was tested by examiningpetrified wood from theHorseshoe Canyon Formation, whereAlbertonykus was found. The wood found there frequently contains borings, which resemble those of termites.
Albertonykus is a member of an unusualtheropod group known as theAlvarezsauridae and is one of only a few alvarezsaurid fossils that has been found outside of South America and Asia.[8] After a phylogenetic analysis, it was shown thatAlbertonykus is a member of the AsiancladeMononykini, which supported the hypothesis that the alvarezsaurs originated in South America, and then dispersed to Asia through North America. The unearthing ofAlbertonykus provided important information into the biology of the Alvarezsauridae.
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