Mononykus
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''Mononykus'' ( , sometimes ; meaning "one claw") is a genus of
alvarezsaurid Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
that lived during the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
in what is now
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
on the
Nemegt Formation The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilians ...
, about 70 million years ago. ''Mononykus'' was a very small theropod, estimated around in length with a weight of . As in ''
Shuvuuia ''Shuvuuia'' is a genus of bird-like theropod dinosaur from the late Cretaceous period of Mongolia. It is a member of the family Alvarezsauridae, small coelurosaurian dinosaurs which are characterized by short but powerful forelimbs specialized ...
'', ''Mononykus'' likely developed a shaggy feathering. It was lightly built with long, thin legs and highly reduced and specialized forelimbs that were likely used for
foraging Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavi ...
termite mound Mound-building termites are a group of termite species that live in mounds which are made of a combination of soil, termite saliva and dung. These termites live in Africa, Australia and South America. The mounds sometimes have a diameter of ...
s or other insect colonies.


History of discovery

''Mononykus'' is represented by a single
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
specimen, catalog number MPC-D 107/6 (formerly IGM 107/6). It was collected in 1987 from the Bügiin Tsav locality of the
Nemegt Formation The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilians ...
,
Gobi Desert The Gobi Desert (, , ; ) is a large, cold desert and grassland region in North China and southern Mongolia. It is the sixth-largest desert in the world. The name of the desert comes from the Mongolian word ''gobi'', used to refer to all of th ...
. This specimen consists of a partial skeleton lacking a tail, and only small fragments of skull bones, including a complete braincase. ''Mononykus'' was originally named '' Mononychus'' in 1993, but later that year, it was renamed because the original name had already been used for a
beetle Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...
named by Johann Schueppel, a German
entomologist Entomology (from Ancient Greek ἔντομον (''éntomon''), meaning "insect", and -logy from λόγος (''lógos''), meaning "study") is the branch of zoology that focuses on insects. Those who study entomology are known as entomologists. In ...
. Several other specimens were later misclassified as ''Mononykus'', 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.Suzuki, S., Chiappe, L. M., Dyke, G.J., Watabe, M., Barsbold, R., and Tsogtbaatar, K. (2002). "A new specimen of ''Shuvuuia deserti'' Chiappe et al., 1998 from the Mongolian Late Cretaceous with a discussion of the relationships of alvarezsaurids to other theropod dinosaurs." ''Contributions in Science'', 494: 1–18. However, these specimens have since been reclassified in the new genus ''
Shuvuuia ''Shuvuuia'' is a genus of bird-like theropod dinosaur from the late Cretaceous period of Mongolia. It is a member of the family Alvarezsauridae, small coelurosaurian dinosaurs which are characterized by short but powerful forelimbs specialized ...
''.Chiappe, L. M., Norell, M. and Clark (1998). "The skull of a relative of the stem-group bird ''Mononykus''." ''Nature'', 392: 275–278. Because of this, many reconstructions of ''Mononykus'' in art and mounted skeletons in museums are in fact based mainly on ''Shuvuuia''. While ''Mononykus'' was formally described in the 1990s, it was reported that a specimen possibly belonging to this genus had already been unearthed by the
Andrews Andrews may refer to: Places Australia *Andrews, Queensland *Andrews, South Australia United States *Andrews, Florida (disambiguation), various places *Andrews, Indiana *Andrews, Nebraska *Andrews, North Carolina *Andrews, Oregon *Andrews, South ...
expedition decades before. The specimen had been in the
American Museum of Natural History The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...
collection, labeled simply as "bird-like dinosaur". However, given the reassignment of the other specimens to related genera, and the difference in age (the AMNH specimen is from the older
Djadochta Formation The Djadochta formation (sometimes transcribed and also known as Djadokhta, Djadokata, or Dzhadokhtskaya) is a highly fossiliferous geological formation in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 million ...
), it is unlikely to be ''Mononykus''.Mortimer, M. (2004)
"Ornithomimosauria"
, ''The Theropod Database'', accessed June 30, 2009.
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 as ''
Gobiraptor ''Gobiraptor'' is a genus of oviraptorid maniraptoran dinosaur from the Maastrichtian-age Nemegt Formation of Mongolia. The type and only species is ''Gobiraptor minutus'', known from a single incomplete specimen—the holotype MPC-D 102/111. It ...
'' and '' Nemegtonykus''.


Description

''Mononykus'' was a small dinosaur around long and weighing . Other characteristics include fused
wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...
bones similar to those of birds, and a keeled breastbone. It differed from close relatives ''
Shuvuuia ''Shuvuuia'' is a genus of bird-like theropod dinosaur from the late Cretaceous period of Mongolia. It is a member of the family Alvarezsauridae, small coelurosaurian dinosaurs which are characterized by short but powerful forelimbs specialized ...
'' and ''
Parvicursor ''Parvicursor'' (meaning "small runner") is a genus of tiny maniraptoran dinosaur with long slender legs for fast running. Discovery and naming The holotype PIN no. 4487/25, mostly consisting of vertebrae, the pelvis and the right hindlimb, w ...
'' 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 of
feathers Feathers are epidermis (zoology), epidermal growths that form a distinctive outer covering, or plumage, on both Bird, avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in ...
, as in the fossils of its relative ''Shuvuuia'' feather traces were discovered, proving that Alvarezsauridae were among the theropod lineages with feathery or downy
integument In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, Exoskeleton, shell, germ or Peel (fruit), rind. Etymology The term is derived from ''integumentum'', which is Latin for "a coverin ...
.Schweitzer, M. H., J. A. Watt, R. Avci, L. Knapp, L. Chiappe, M. Norell & M. Marshall. (1999). "Beta-keratin specific immunological reactivity in feather-like structures of the Cretaceous alvarezsaurid, ''Shuvuuia deserti''." ''Journal of Experimental Zoology'', 285: 146–157. The
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...
structures of ''Mononykus'' and its relatives closely resembles those of Barn Owls. For this reason it is possible ''Mononykus'' also had a
facial disc In ornithology, the facial disc is the concave collection of feathers on the face of some birds—most notably owls—surrounding the eyes. The concavity of the facial disc forms a circular paraboloid that collects sound waves and directs those ...
of specialized feathers, similar to
extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...
owls, that served to catch sound and direct it to the ears.


Paleobiology

''Mononykus'' was a member of the family
Alvarezsauridae Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...
and, like its relatives, had very strange, stubby forearms with one large, approximately long claw (hence its name). The other two claws had disappeared (however, a close relative of ''Mononykus'', ''
Shuvuuia ''Shuvuuia'' is a genus of bird-like theropod dinosaur from the late Cretaceous period of Mongolia. It is a member of the family Alvarezsauridae, small coelurosaurian dinosaurs which are characterized by short but powerful forelimbs specialized ...
'', had two
vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
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 open
termite Termites are a group of detritivore, detritophagous Eusociality, eusocial cockroaches which consume a variety of Detritus, decaying plant material, generally in the form of wood, Plant litter, leaf litter, and Humus, soil humus. They are dist ...
mounds (like modern
anteaters Anteaters are the four extant mammal species in the suborder Vermilingua (meaning "worm tongue"), commonly known for eating ants and termites. The individual species have other names in English and other languages. Together with sloths, they ar ...
), and therefore it is possible that they fed primarily on insects.Senter, P. (2005). "Function in the stunted forelimbs of ''Mononykus olecranus'' (Theropoda), a dinosaurian anteater". ''Paleobiology'' Vol. 31, No. 3 pp. 373–381. In a 2001 study conducted by Bruce Rothschild and other paleontologists, 15 foot bones referred to ''Mononykus'' were examined for signs of
stress fracture A stress fracture is a fatigue-induced bone fracture caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated injury from repeated submaximal loading, such as running ...
, but none were found.Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331–336.


References


External links


In chinese but with pictures and taxon in english
{{Taxonbar, from=Q131421 Alvarezsauridae Dinosaur genera Maastrichtian dinosaurs Nemegt Formation Fossil taxa described in 1993 Taxa named by Altangerel Perle Taxa named by Luis M. Chiappe Dinosaurs of Mongolia