''Ceratonykus'' (meaning "horned claw") is a

monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

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 period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

that lived during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', the ...

(late

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

stage, 72.1 Ma) in what is now the

Barun Goyot Formation The Barun Goyot Formation (also known as Baruungoyot Formation or West Goyot Formation) is a geological formation dating to the Late Cretaceous Period. It is located within and is widely represented in the Gobi Desert Basin, in the Ömnögovi Pr ...

. The type and only species, ''Ceratonykus oculatus'', is known from a fragmentary

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

, including an incomplete

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

, of an adult individual. It was named and described in

2009 File:2009 Events Collage V2.png, From top left, clockwise: The vertical stabilizer of Air France Flight 447 is pulled out from the Atlantic Ocean; Barack Obama becomes the first African American to become President of the United States; 2009 Iran ...

by Vladimir Alifanov and

Rinchen Barsbold , Rinchyengiin Barsbold, born December 21, 1935 in Ulaanbaatar) is a Mongolian paleontologist and geologist. He works with the Institute of Geology, at Ulaanbaatar, Mongolia. He is an expert in vertebrate paleontology and Mesozoic stratigraphy. Bar ...

. Its describers questioned the traditional placement of alvarezsaurs in

Theropoda Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ca ...

, instead suggesting they were

ornithischians Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...

, but this has not been accepted since. ''Ceratonykus'' has an estimated length of 75 centimetres (2.5 feet) and weight of 760 grams (1.68 lbs). It has been considered as a possible

junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

of ''

Parvicursor ''Parvicursor'' (meaning "small runner") is a genus of tiny maniraptoran dinosaur with long slender legs for fast running. At only about from snout to end of tail, and in weight, it was initially seen as one of the smallest non-avian dinosaur ...

''.

Discovery and naming

Cretaceous-aged dinosaur fossil localities of Mongolia

In 2003, a partial

of an

was discovered in the

of the Khermiin Tsav locality,

by the Paleontological Center of the Mongolian Academy of Sciences (MPC) preparator Otkhoon Zhargal. The skeleton was enclosed in two pieces of rock during the time of the discovery. The specimen was subsequently named and described in

by Vladimir Alifanov and

. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen, MPC no. 100/124, consists of an incomplete

and

lower jaw In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

, cervical

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

e, caudal vertebrae,

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sh ...

, left and right

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

s, a right

humeral The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a rou ...

fragment, distal elements of forelimbs, fragmentary ilium, and hindlimbs. The specimen is of an adult individual based on the fusion of the astragali and

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

e, with partially obliterated sutures. The

generic Generic or generics may refer to: In business * Generic term, a common name used for a range or class of similar things not protected by trademark * Generic brand, a brand for a product that does not have an associated brand or trademark, other ...

name, ''Ceratonykus'', is derived from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

words "''ceratinus''" (horned) and "''onyx''" (claw). The

specific Specific may refer to: * Specificity (disambiguation) * Specific, a cure or therapy for a specific illness Law * Specific deterrence, focussed on an individual * Specific finding, intermediate verdict used by a jury in determining the fina ...

name, ''oculatus'', is derived from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

word "''oculatus''" (sharp-sighted, big-eyed).

Description

Size and distinguishing traits

In 2016,

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...

gave ''Ceratonykus'' an estimated length of 0.6 metres (2 feet) and weight of 1 kilogram (2 lbs).Paul, G.S., 2016, ''The Princeton Field Guide to Dinosaurs 2nd Edition'', Princeton University Press However, Molina-Pérez and Larramendi (2016) gave ''Ceratonykus'' an estimated length of 75 centimetres (2.5 feet) and weight of 760 grams (1.68 lbs). Alifanov & Barsbold (2009) originally diagnosed ''Ceratonykus'' based on the long preorbital

region; an upper

temporal fenestrae The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

ovate that was 0.4 as long as the frontals; the length of the frontal being almost four times greater than its width; the frontals narrowing towards the rostrum into a narrow wedge; the prefrontals adjoining each other towards the middle; the basipterygoid processes being two-thirds as high as the quadrates; the

dentaries In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

form a deep and rostrally tapering depression; extensive

mandibular fenestrae The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

; narrow

centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different ...

cervical In anatomy, cervical is an adjective that has two meanings: # of or pertaining to any neck. # of or pertaining to the female cervix: i.e., the ''neck'' of the uterus. *Commonly used medical phrases involving the neck are **cervical collar **cerv ...

and anterior

caudal vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

; the

deltopectoral crest Deltopectoral may refer to; * Clavipectoral triangle, also known as the deltopectoral triangle * Deltopectoral groove * Deltopectoral lymph nodes One or two deltopectoral lymph nodes (or infraclavicular nodes) are found beside the cephalic vein, b ...

being separated from the

humeral head The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a round ...

by a notch; the basal

phalanx The phalanx ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar pole weapons. The term is particularly use ...

of the major digit of the manus is extended, with its flanks moderately wide, and a narrow and symmetrical distal condyle; the postacetabular plate of the ilia possessing a relatively small longitudinal craniomedial crest; a strongly curved

femora The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with t ...

that is nearly half as long as

tibiotarsus The tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia. A similar structure also occurred in the Mesozoic Heterodontosauridae. These sm ...

; a distinct fourth

trochanter A trochanter is a tubercle of the femur near its joint with the hip bone. In humans and most mammals, the trochanters serve as important muscle attachment sites. Humans are known to have three trochanters, though the anatomic "normal" includes ...

; an undeveloped

cnemial crest The cnemial crest is a crestlike prominence located at the front side of the head of the tibiotarsus or tibia in the legs of many mammals and reptiles (including birds and other dinosaurs). The main extensor muscle of the thigh In human anat ...

of the

e; an ascending process of the astragali that is high and wide; the tarsometatarsals being 1.33 as long as the femora; the second and fourth

metatarsals The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...

tightly adjoining each other over its entire extent; a deep notch that is formed proximodorsally between the metatarsals; the second metatarsals being shorter than the fourth distally; tarsometatarsals that are 3.5 times as long as the third metatarsals; and the basal phalanx of the fourth digit of the hind feet only being slightly shorter than the basal phalanx of second digit.

Cranium

The part of the skull nearest to the

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

is narrow and extended, with a deep occipital region and large

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

. The

antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, bird ...

e were at least half as large as the orbits and the temporal bars are relatively small, while the lower

are narrow and slightly lower in height than the diameter of the orbits. Both of the frontals are paired, however, the left frontal is missing the posteromedial margin while the right frontal is only known from the rostral end. Both frontals are four times as long as wide, similar to ''Shuvuuia'', and are narrow wedge-shaped in front view. The

squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral c ...

s adjoin the

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...

and the paroccipital process, while also being relatively short and t-shaped. The postorbital bones have a large medial process and connect to the parietal and frontal by a different process. The ventral process of the

lacrimals The lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the Orbit (anatomy), orbit. It has two surfaces and four borders. Several ...

are narrow with the dorsal process being very long and rod-like. Both the jugals and the quadratojugals circular in cross section and are fused but do not form a suture. The quadrates are high, with the distal condyle being present on the occipital crest and the lateral crest being connected to the upper side of the contact zone of the squamosal and postorbital bones. As in ''Shuvuuia'', a notch is present in between the lateral and occipital condyles. The paroccipital processes of the braincase are compressed towards the upper side and underside. The interior of the prootics have a coarse-cellular structure, which can only be viewed on the right side of the skull. The

basioccipital The basilar part of the occipital bone (also basioccipital) extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline. In the young skull this area is rough and uneven, and is joined t ...

forms an occipital condyle on a long and wide neck, while exoccipitals do no not form a part of the condyle. Unlike ''Shuvuuia'', the basipterygoid processes diverge at almost 60° and are almost two-thirds as long as the quadrates. The

are long, with the rostral end slightly expanding vertically and curving downwards. The

have a wide oval shape and an anterior border that is in line with the border between the first and second thirds of the orbits. The lower jaw rami form the para-articular processes, which are in line with the quadrate–mandibular articulation. The base of the right occipital process contained a cavity. A coarse-cellular structure is seen on the right side of the skull. The body of the basioccipital forms an occipital condyle, while the exoccipitals do not form a part of the condyle. The sphenoccipital tubercles are separated by a wide groove and a depression is present in the contact area of the basioccipital and basisphenoid. The basisphenoid coincides with the basipterygoid processes, which slightly compresses towards the sides and middle. The cerebral hemispheres constitute a majority of the brain. These cerebral hemi-spheres are separated from the midbrain by the presence of a sulcus and preserve traces of the brain membrane. An interhemispheric sulcus is present at the start of the

olfactory tract The olfactory tract is a bilateral bundle of afferent nerve fibers from the mitral and tufted cells of the olfactory bulb that connects to several target regions in the brain, including the piriform cortex, amygdala, and entorhinal cortex. It ...

s. The optic lobes are displaced towards the anterior, which is a characteristic of extant birds. The eyeballs would have been positioned towards the brain and are a quarter of the head length in diameter, a feature that suggests the eyesight of

alvarezsaurs Alvarezsauroidea is a group of small maniraptoran dinosaurs. Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez (historian), Gregorio Álvarez, not the more familiar physicist Luis Walter Alvarez, L ...

were the key afferent system. The acoustic tubercles are unusually wide and are positioned between the occipital edge of the cerebral hemispheres and

cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...

Postcrania

The

atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...

is likely represented by the intercentrum, which is low and elongated with the posterior region being broken off. There is a vertically positioned bone that is present on the fragment that likely represents the

neural arch The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

of the atlas. The series of three cervical vertebrae lack

pleurocoels Skeletal pneumaticity is the presence of air spaces within bones. It is generally produced during development by excavation of bone by pneumatic diverticula (air sacs) from an air-filled space, such as the lungs or nasal cavity. Pneumatization is h ...

and has

condyles A condyle (;Entry "condyle"
in
Mononykus ''Mononykus'' ( , sometimes ; meaning "one claw") is a genus of alvarezsaurid dinosaur that lived during the Late Cretaceous in what is now Asia on the Nemegt Formation, about 70 million years ago. ''Mononykus'' was a very small theropod, estim ...

'' and are slightly more narrower than those of ''

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 f ...

''. The diapophyses on the first two vertebrae of the series are relatively small but are wider at the base and extend towards the sides and underside. The parapophyses are separated by a ventral groove from each other and connect to the diapophyses by a narrow crest on the middle vertebra. The

of this vertebra is wide and low, with the neural spine being completely absent. The first free

caudal vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

has a centrum that is narrow and is moderately high, with a small ventral keel being present near the condyle. Much like the first free caudal vertebra, the three articulated anterior caudal vertebrae have a centrum that is narrow but are high over the entire extent. Different to the first free caudal vertebra and the three articulated anterior caudal vertebrae are two isolated vertebrae of the middle caudal region that have a low centrum, and a barely viewable crest in place of the neural spine. However, all caudal vertebrae are procoelous. The

of the

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of t ...

is an unpaired bone that lacks a pronounced medial keel. The side surface of the

s is convex, with the posterodorsal edge being thickened and a short crest forming close to the posterosuperior margin. The base of the

was inclined caudally. The deltopectoral crest was separated from the humeral head by a notch, with the upper region resembling a high process based on the rounded outline of the base and foramen in the centre. ''Ceratonykus'' has a basal

of the major digit that is similar to that of ''Mononykus'', but differs in the narrower distal part. The second

carpometacarpus The carpometacarpus is a bone found in the hands of birds. It results from the fusion of the carpal and metacarpal bone, and is essentially a single fused bone between the wrist and the knuckles. It is a smallish bone in most birds, generally flat ...

possesses two spike like bones that range in size which may have been terminal phalanges of digits rather. The posterior plate of the left ilium is wide and flat, with the side margin being arched and the craniomedial part having a longitudinal crest. The

lack

epiphyses The epiphysis () is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the join ...

and are convex in the proximal part, while the medial surface is straight. The

e also lacks epiphyses and the tibiotarsals are slightly curved towards the sides in the upper half. The tibiae are subcircular in cross section and lack a projecting part of the external cnemial crest, with the astragali being completely fused to the bones. The

are one and a third times as long as the femora, with the tarsometatarsus being three and a half times as long as the third metatarsals. Dorsal and palmar grooves are present in the area of connection of the metatarsals and tarsometatarsus, but disappear in the lower palmar third of the tarsometatarsals. As in ''

'', the second metatarsals were shorter than the fourth metatarsals, with the metatarsals being widened in the middle part in side view. Due to the poor preservation of the holotype specimen, the shape of articular facets of the metatarsals and digits is not known. Found in natural articulation were the basal phalanges of the second and third digits of the right foot. ''Ceratonykus'' has a similar ratio of the lengths of basal phalanges as ''Mononykus'' as the larger basal phalanx of the fourth digit is slightly shorter than the basal phalanx of the second digit, and the basal phalanx of the third digit is slightly longer than the basal phalanx of the second digit.

Classification

Alifanov & Barsbold (2009) originally placed ''Ceratonykus'' within

Alvarezsauria Alvarezsauroidea is a group of small maniraptoran dinosaurs. Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez, not the more familiar physicist Luis Alvarez, or his son geologist Walter Alvarez ...

, within the clade Parvicursoridae, as sister taxon to ''

Mononykus ''Mononykus'' ( , sometimes ; meaning "one claw") is a genus of alvarezsaurid dinosaur that lived during the Late Cretaceous in what is now Asia on the Nemegt Formation, about 70 million years ago. ''Mononykus'' was a very small theropod, estim ...

''. The authors questioned the traditional placement of Alvarezsauria within

, instead suggesting they were

, but since then this has not been accepted. Qin ''et al.'' (2019) recovered ''Ceratonykus'' within a

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...

with ''

Linhenykus ''Linhenykus'' is an extinct genus of alvarezsaurid theropod dinosaur from the Late Cretaceous of Inner Mongolia, China. It is the most basal known member of the Parvicursorinae. The genus gets its name from Linhe, a city near the site where t ...

,'' ''

'', ''Mononykus'' and ''Parvicursor'', a position also recovered by Xu ''et al.'' (2018). Lee ''et al.'' (2019) recovered it in a similar position, but with the inclusion of ''

Nemegtonykus ''Nemegtonykus'' (meaning "Nemegt claw" after the Nemegt Formation where it was found) is a genus of alvarezsaurid dinosaur from the Nemegt Formation in Mongolia. The type and only species is ''Nemegtonykus citus''. It is the second alvarezsaur ...

'' and a clade containing '' Kol'', ''

Xixianykus ''Xixianykus'' is a genus of alvarezsaurid theropod dinosaur from the late Cretaceous period of China.Xu, X., Wang, D.Y., Sullivan, C., Hone, D.W.E., Han, F.L., Yan, R.H. and Du, F.M. (2010). "A basal parvicursorine (Theropoda: Alvarezsauridae) ...

'' and '' Albinykus''. In addition, it was also recovered within a polytomy by Fowler ''et al.'' (2020), with the inclusion of ''

Trierarchuncus ''Trierarchuncus'' (meaning "captain hook," after its single-clawed hands) is a monotypic genus of alvarezsaurid theropod which includes a single species, ''Trierarchuncus prairiensis'', which is known from fossils found in deposits of the Hell C ...

'', and Averianov & Lopatin (2021), with the inclusion of ''

Khulsanurus ''Khulsanurus'' (meaning "tail from Khulsan") is an extinct genus of alvarezsaurid theropod dinosaur from the Late Cretaceous Barungoyot Formation of the Khulsan Locality in the Gobi Desert region of Mongolia. The type and only species is ''Khu ...

'', in a strict consensus tree using unweighted characters. However, a strict consensus tree with implied weighting by Averianov & Lopatin (2021) placed it as sister taxon to ''Parvicursor''. Agnolin ''et al.'' (2012) positioned ''Ceratonykus'' within the tribe Ceratonykini, as sister taxon to ''Xixianykus'' and ''Albinykus''. Averianov & Lopatin (2022b) considered ''Ceratonykus'' to be a

of ''Parvicursor'' as the differences between both taxa were minimal and concerned characters that are likely to be

ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...

and possibly also individual variation. A phylogenetic analysis conducted by Averianov & Lopatin (2022b) is reproduced below. The results of an earlier analysis by Agnolin ''et al.'' (2012) are reproduced below.

Paleobiology

In 2011, Vladimir Alifanov and Sergey Savelyev described the natural

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

cast of ''Ceratonykus''. The authors noted that the brain anatomy is a linear structure, with no bends in the parasagittal plane at the boundaries between the

mesencephalon The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', "m ...

and

myelencephalon The myelencephalon or afterbrain is the most posterior region of the embryonic hindbrain, from which the medulla oblongata develops. Development Neural tube to myelencephalon During fetal development, divisions of the neural tube that give ...

, a feature that is not seen in

crocodiles Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant memb ...

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

and other

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

. The visual and auditory analysers are represented by separate lobes in the midbrain, with the optic lobes being displaced ventrolaterally like that of birds. Alifanov and Savelyev tested the hypothesis of climbing ancestors of

by looking at the

of ''Ceratonykus'', which has at least one transverse sulcus as in crocodiles but not lizards. Due to crocodiles having a better coordination of movements than lizards, as they need to orient themselves in three dimensional space, the authors proposed that the ancestor of alvarezsaurs were likely

arboreal Arboreal locomotion is the Animal locomotion, locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. Th ...

. The authors also suggested that the complex cerebellum could have been useful for efficient regulation of the speed and numerous movement patterns such as jumping in terrestrial alvarezsaurs. Additionally, they considered that specialization of the eyesight, hearing and sense of smell might have made alvarezsaurs efficient for searching for food and hunting. Agnolín ''et al.'' (2021) also noted that the enlarged

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

of the neck and the expansion of the cerebellum of ''Ceratonykus'' suggests a locomotor improvement in alvarezsaurs.

Paleoenvironment

''Ceratonykus'' is known from the Barun Goyot Formation, which has been dated to the

stage of the

period. The Barun Goyot Formation has a thickness of 110 metres (360 feet) and overlies the

Djadokhta Formation The Djadochta Formation (sometimes transcribed and also known as Djadokhta, Djadokata, or Dzhadokhtskaya) is a highly fossiliferous geological formation situated in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 mill ...

. The

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

s of the formation were deposited in various conditions, with the lower part consisting of alternating

dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...

deposits and

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s that existed in interdune areas, while the upper part consisted of sediments that were deposited over an area similar to takyrs that was flooded at irregular intervals. Overall, the formation had a

semi-arid climate A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-ar ...

with significant

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...

fall. The fauna of the Barun Goyot Formation consists of the alvarezsaurids ''

'', ''

Ondogurvel ''Ondogurvel'' () (meaning "egg lizard") is a genus of alvarezsaurid dinosaur from the Late Cretaceous (Campanian) Barun Goyot Formation in southern Mongolia. The type and only species is ''O. alifanovi'', known from a partial skeleton consisting ...

'' and ''Parvicursor'', the ankylosaurine ankylosaurids ''

Saichania ''Saichania'' (Mongolian meaning "beautiful one") is a genus of herbivorous ankylosaurid dinosaur from the Late Cretaceous period of Mongolia and China. The first fossils of ''Saichania'' were found in the early 1970s in Mongolia. In 1977 the ...

'', ''

Tarchia ''Tarchia'' (meaning "brainy one") is a genus of herbivorous ankylosaurid dinosaur from the late Cretaceous of Mongolia. Discovery and naming In 1970, a Polish-Mongolian expedition discovered an ankylosaurian skull near Khulsan. In 1977, Ter ...

'', ''

Zaraapelta ''Zaraapelta'' is an extinct genus of herbivorous ankylosaurid thyreophoran dinosaur from the Late Cretaceous of Mongolia. The type species is ''Zaraapelta nomadis'', named and described by Arbour ''et al'' in 2014. ''Zaraapelta'' is known from ...

'' and an indeterminate ankylosaurid; the

ceratopsia Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...

ns ''

Bagaceratops ''Bagaceratops'' (meaning "small-horned face") is a genus of small protoceratopsid dinosaurs that lived in Asia during the Late Cretaceous, around 72 to 71 million years ago. ''Bagaceratops'' remains have been reported from the Barun Goyot Form ...

'', ''

Breviceratops ''Breviceratops'' (meaning "short horned face") is a genus of protoceratopsid dinosaur that lived during the Late Cretaceous in what is now the Barun Goyot Formation, Mongolia. Discovery and naming The first fossils were discovered during the ...

'' and possibly ''

Udanoceratops ''Udanoceratops'' (meaning "Udan's horned face") is a genus of large leptoceratopsid dinosaur that lived during the Late Cretaceous period of Mongolia, in what is now the Djadokhta Formation. Discovery ''Udanoceratops'' was first named and d ...

;'' the

velociraptorine Velociraptorinae is a subfamily of the theropod group Dromaeosauridae. The earliest velociraptorines are probably ''Nuthetes'' from the United Kingdom, and possibly '' Deinonychus'' from North America. However, several indeterminate velociraptori ...

dromaeosaurids Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...

Kuru Kuru may refer to: Anthropology and history * Kuru (disease), a type of transmissible spongiform encephalopathy associated with the cannibalistic funeral practices of the Fore people * Kuru (mythology), part of Meithei mythology * Kuru Kingdom, ...

'' and ''

Shri Shri (; , ) is a Sanskrit term denoting resplendence, wealth and prosperity, primarily used as an honorific. The word is widely used in South and Southeast Asian languages such as Marathi, Malay (including Indonesian and Malaysian), Javanese, ...

;'' the halszkaraptorine unenlagiid ''

Hulsanpes ''Hulsanpes'' ( meaning " Khulsan foot") is a genus of halszkaraptorine theropod dinosaurs that lived during the Late Cretaceous in what is now the Barun Goyot Formation of Mongolia, about 75-72 million years ago. The remains were found in 1970 a ...

;'' the

pachycephalosaurid Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephal ...

Tylocephale ''Tylocephale'' (meaning "swollen head", from the Greek ''τυλη'' meaning 'callus' or 'hard swelling' and ''κεφαλη'' meaning 'head') is a genus of pachycephalosaurid dinosaur from the Late Cretaceous period. It was a herbivorous dinos ...

;'' the

oviraptorids Oviraptoridae is a group of bird-like, herbivorous and omnivorous maniraptoran dinosaurs. Oviraptorids are characterized by their toothless, parrot-like beaks and, in some cases, elaborate crests. They were generally small, measuring between on ...

Conchoraptor ''Conchoraptor'' (meaning "conch plunderer") is a genus of oviraptorid dinosaurs that lived in Asia during the Late Cretaceous epoch, about 70 million years ago. It is known from the Barun Goyot and Nemegt formations of Mongolia. Discovery Wh ...

'', ''

Heyuannia ''Heyuannia'' ("from Heyuan") is a genus of oviraptorid dinosaur that lived in Asia during the Late Cretaceous epoch, in what is now China and Mongolia. It was the first oviraptorid found in China; most others were found in neighbouring Mongoli ...

'' and ''

Nemegtomaia ''Nemegtomaia'' is a genus of oviraptorid dinosaur from what is now Mongolia that lived in the Late Cretaceous Period (geology), Period, about 70million years ago. The first specimen was found in 1996, and became the basis of the new genus and s ...

'', the

titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...

'' Quaesitosaurus;'' the

enantiornithines The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...

Gobipteryx ''Gobipteryx'' (from Gobi eferring to the Gobi Desert where it was first discovered and Greek pteryx “wing”) is a genus of prehistoric bird from the Campanian Age (geology), Age of the Late Cretaceous Period (geology), Period.Elżanowski, ...

'' and '' Gobipipus;'' Kurochkin, E. N.; Chatterjee, S.; Mikhailov, K. E. (2013). An embryonic enantiornithine bird and associated eggs from the cretaceous of Mongolia. Paleontol. J. 47, 1252–1269. and the

ornithuromorph Euornithes (from Greek ' meaning "true birds") is a natural group which includes the most recent common ancestor of all avialans closer to modern birds than to ''Sinornis''. Description Clarke ''et al''. (2006) found that the most primitive know ...

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

'' Hollanda.Bell, A.K., Chiappe, L.M., Erickson, G.M., Suzuki, S., Watabe, M., Barsbold, R. and Tsogtbaatar, K. (2010). "Description and ecologic analysis of ''Hollanda luceria'', a Late Cretaceous bird from the Gobi Desert (Mongolia)." ''Cretaceous Research'', 31(1): 16-26.

References

{{Taxonbar, from=Q675014 Alvarezsaurids Late Cretaceous dinosaurs of Asia Fossil taxa described in 2009 Taxa named by Rinchen Barsbold