| Mononykus | |
|---|---|
 | |
| Reconstructed skeleton at theAmerican Museum of Natural History | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Alvarezsauridae |
| Subfamily: | †Parvicursorinae |
| Tribe: | †Mononykini |
| Genus: | †Mononykus Perleet al., 1993[1] |
| Type species | |
| †Mononykus olecranus Perleet al., 1993[1] | |
| Synonyms | |
Mononychus olecranusPerleet al., 1993[1] (preoccupied generic name) | |
Mononykus (/məˈnɒnɪkəs/mə-NON-ik-əs, sometimes/ˌmɒnoʊˈnaɪkəs/MON-oh-NY-kəs; meaning "one claw") is a genus ofalvarezsauriddinosaur that lived during theLate Cretaceous in what is nowMongolia, specifically theNemegt Formation, about 70 million years ago.Mononykus was a very small theropod, estimated around 1 to 1.2 metres (3.3 to 3.9 ft) in length with a weight of 3.5 kilograms (7.7 lb). As inShuvuuia,Mononykus likely developed a shaggy feathering. It was lightly built with long, thin legs and highly reduced and specialized forelimbs that were likely used forforagingtermite mounds or other insect colonies.
Mononykus is represented by a singleholotype specimen, catalog numberMPC-D 107/6 (formerly IGM 107/6). It was collected in 1987 from the Bügiin Tsav locality of theNemegt Formation,Gobi Desert. This specimen consists of a partial skeleton lacking a tail, and only small fragments of skull bones, including a complete braincase.[1][2]Mononykus was originally namedMononychus in 1993, but later that year, it was renamed because the original name had already been used for abeetle named byJohann Schueppel, a Germanentomologist.[3] Several other specimens were later misclassified asMononykus, including specimens with partial tails (initially misinterpreted as being very short, though later specimens showed they were long and thin) and complete skulls showing a distinct, mostly toothless form.[4] However, these specimens have since been reclassified in the new genusShuvuuia.[5] Because of this, many reconstructions ofMononykus in art and mounted skeletons in museums are in fact based mainly onShuvuuia.
WhileMononykus was formally described in the 1990s, it was reported that a specimen possibly belonging to this genus had already been unearthed by theAndrews expedition decades before. The specimen had been in theAmerican Museum of Natural History collection, labeled simply as "bird-like dinosaur".[6] However, given the reassignment of the other specimens to related genera, and the difference in age (the AMNH specimen is from the olderDjadochta Formation), it is unlikely to beMononykus.[7]
In 2019, Sungjin Lee and colleagues referred a new specimen from the Nemegt Formation, MPC-D 100/206. This specimen consists of seven caudal vertebrae with a partial left hindlimb, and was discovered on a low slope of the Altan Uul III locality in 2008 by an international team of the Korea-Mongolia International Dinosaur Expedition (KID). The team also found a small assemblage of theropod fossils comprising specimens from other taxa such asGobiraptor andNemegtonykus.[8]
Mononykus was a small dinosaur around 1 to 1.2 metres (3.3 to 3.9 ft) long and weighing 3.5 kilograms (7.7 lb).[9][10] Other characteristics include fusedwrist bones similar to those of birds, and a keeled breastbone. It differed from close relativesShuvuuia andParvicursor in several details of its skeleton, including a pubic bone that is triangular in cross section, and different proportions in the toe bones.Mononykus likely had a covering offeathers, as in the fossils of its relativeShuvuuia feather traces were discovered, proving that Alvarezsauridae were among the theropod lineages with feathery or downyintegument.[11] Theinner ear structures ofMononykus and its relatives closely resembles those of Barn Owls.[12][13] For this reason it is possibleMononykus also had afacial disc of specialized feathers, similar toextant owls, that served to catch sound and direct it to the ears.[12]
Mononykus was a member of the familyAlvarezsauridae and, like its relatives, had very strange, stubby forearms with one large, approximately 7.5-centimetre (3.0 in) long claw (hence its name). The other two claws had disappeared (however, a close relative ofMononykus,Shuvuuia, had twovestigial claws, alongside one large claw). The purpose of these highly specialized arms is still a mystery, but some scientists have suggested they were used to break opentermite mounds (like modernanteaters), and therefore it is possible that they fed primarily on insects.[14]
In a 2001 study conducted by Bruce Rothschild and other paleontologists, 15 foot bones referred toMononykus were examined for signs ofstress fracture, but none were found.[15]
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