''Hypnovenator'' (meaning "sleep hunter") is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of

troodontid Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...

theropod dinosaurs from the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

(

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

)

Ohyamashimo Formation The Ohyamashimo Formation(大山下層) is an Early Cretaceous (Albian) geologic formation in Japan. It has been dated to the early-mid Albian, between 112.1 ± 0.4 Ma and 106.4 ± 0.4 Ma. Dinosaur remains have been discovered from this formatio ...

of Japan. The genus contains a single species, ''H. matsubaraetoheorum'', known from a partial skeleton. ''Hypnovenator'' is the only troodontid currently known from Japan, and it represents the oldest definitive member of the subgroup Troodontinae.

Discovery and naming

Locality maps and geology in Tambasasayama

The ''Hypnovenator''

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, MNHAH D1033340, was discovered in sediments of the

(lower Sasayama Group) in Nishikosa,

Tamba-Sasayama , formerly known as , is a city in the central eastern part of Hyōgo Prefecture, Japan. , the city had an estimated population of 40,050 in 17,523 households and a population density of 110 persons per km2. The total area of the city is Geograp ...

city, of

Hyōgo Prefecture is a Prefectures of Japan, prefecture of Japan located in the Kansai region of Honshu. Hyōgo Prefecture has a population of 5,469,762 () and a geographic area of . Hyōgo Prefecture borders Kyoto Prefecture to the east, Osaka Prefecture to th ...

, Japan. Much of the known material was discovered in September 2010 by a group of amateur fossil hunters during the construction of the Hyogo Prefectural Tamba Namikimichi Central Park. Subsequent expeditions in July of the following year by the prefecture's Museum of Nature and Human Activities revealed an additional block containing material belonging to the same individual. The specimen is somewhat fragmentary, comprising bones of both the axial and

appendicular skeleton The appendicular skeleton is the portion of the vertebrate endoskeleton consisting of the bones, cartilages and ligaments that support the paired appendages ( fins, flippers or limbs). In most terrestrial vertebrates (except snakes, legless li ...

. These include two

caudal vertebrae Caudal vertebrae are the vertebrae of the tail in many vertebrates. In birds, the last few caudal vertebrae fuse into the pygostyle, and in apes, including humans, the caudal vertebrae are fused into the coccyx. In many reptiles, some of the caud ...

with a

chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * '' Eulithis testata'', a moth * Chevron (geology), a fold in rock la ...

, two

ribs The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great vessels ...

, several

gastralia Gastralia (: gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these reptil ...

, most of the left arm—including the

humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

carpal The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In huma ...

metacarpals In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular skeleton, appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones (wrist, wris ...

, and most of the

phalanges The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...

and manual

ungual An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanges, as did the sauropod Sauropoda (), whose members are known as sauropods (; ...

s—and some of the legs, including part of the left

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

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

, and

fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

, right tibia, both astragali, and several partial

metatarsal The metatarsal bones or metatarsus (: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges ( toes). Lacking individual names, the metatarsal bones are ...

s and pedal

(toe bones). HypnovenatorSize

Prior to a formal description of the fossil material, it was mentioned in

conference A conference is a meeting, often lasting a few days, which is organized on a particular subject, or to bring together people who have a common interest. Conferences can be used as a form of group decision-making, although discussion, not always d ...

abstracts An abstract is a brief summary of a research article, thesis, review, conference proceeding, or any in-depth analysis of a particular subject and is often used to help the reader quickly ascertain the paper's purpose. When used, an abstract always ...

in 2012 and 2023. It was also mentioned in a

Research Square Research Square is an open-access platform of electronic preprints approved for posting after moderation, but not peer review. The predecessor of Research Square was American Journal Experts. The platform, Research Square, was established in 2013 ...

preprint In academic publishing, a preprint is a version of a scholarly or scientific paper that precedes formal peer review and publication in a peer-reviewed scholarly or scientific journal. The preprint may be available, often as a non-typeset versi ...

in early 2024, under the

binomial name In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...

"Hypnovenator sasayamaensis". In mid-2024, Katsuhiro Kubota,

Yoshitsugu Kobayashi Yoshitsugu Kobayashi (小林快次, ''Kobayashi Yoshitsugu'', born 1971) is a Japanese vertebrate paleontologist. He is a professor and the assistant director in Hokkaido University Museum. His major achievements include the description and nami ...

, and Tadahiro Ikeda described ''Hypnovenator matsubaraetoheorum'' as a new genus and species of troodontid dinosaurs based on these fossil remains. The generic name, ''Hypnovenator'', is combines the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

word "''hypnos''", meaning "sleep", with the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word "''venator''", meaning "hunter", referencing the sleeping position the holotype was preserved in, similar to some Chinese troodontids like '' Mei'' and ''

Sinornithoides ''Sinornithoides'' (meaning "Chinese bird form") is a genus of troodontid theropod dinosaurs containing the single species ''Sinornithoides youngi''. ''S. youngi'' lived during the Early Cretaceous (Aptian/Albian stage, around 113 million years ...

''. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, ''matsubaraetoheorum'', honors Kaoru Matsubara and Takaharu Ohe the discoverers of the ''Hypnovenator'' holotype. ''Hypnovenator'' represents the twelfth validly named non-avian dinosaur described from

Mainland Japan is a term used to distinguish Japan's core land area from its outlying territories. "Mainland Japan" was an official term in the pre-war period, distinguishing Japan proper from its overseas territories (外地, ''gaichi'', lit. "outer lands ...

Classification

Kubota et al. (2024) scored the ''Hypnovenator'' fossil material into

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

matrix of Sellés et al. (2021), itself a derivative of a large phylogenetic analysis intended to test the relationships of all major maniraptoromorph groups. Kubota et al. recovered it as a basal member of the Troodontinae, as the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of the younger Mongolian ''

Gobivenator ''Gobivenator'' is an extinct genus of troodontid theropod dinosaur known from the late Campanian Djadokhta Formation of central Gobi Desert, Mongolia. It contains a single species, ''Gobivenator mongoliensis''. ''G. mongoliensis'' is known from ...

'', making ''Hypnovenator'' the oldest known troodontine. Their results are displayed in the

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below:

Paleoecology

''Hypnovenator'' is known from the Ohyamashimo Formation (Sasayama Group), which dates to the early–middle

age from the end of the

. These layers are predominantly made up by

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

s, and conglomerates. The

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will b ...

represents a

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

system with a subhumid to

semi-arid A semi-arid climate, semi-desert climate, or steppe climate is a aridity, dry climate sub-type. It is located on regions that receive precipitation below Evapotranspiration#Potential evapotranspiration, potential evapotranspiration, but not as l ...

climate. Named dinosaur taxa from the formation include the

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

Sasayamagnomus ''Sasayamagnomus'' (meaning "Gnome from Sasayama") is a genus of neoceratopsian dinosaur from the Early Cretaceous (Albian) Ohyamashimo Formation of Hyogo prefecture, Japan. The genus contains a single species, ''S. saegusai''. Type specimen i ...

'' and the

titanosauriform Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence ...

sauropod '' Tambatitanis''. The

monstersauria Monstersauria is a clade of Anguimorpha, anguimorph lizards, defined as all taxa more closely related to ''Heloderma'' than ''Varanus''. It includes ''Heloderma'', as well as several extinct genera, such as ''Estesia'', ''Primaderma'' and ''Gobid ...

n lizard ''

Morohasaurus ''Morohasaurus'' is an extinct genus of ''cf.'' monstersaurian squamates know from a single left dentary from the Early Cretaceous (?Albian) Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan. The type and only ...

'' has also been described. Dinosaur teeth are common in various localities throughout this formation including those belonging to other theropods (

dromaeosaurid Dromaeosauridae () is a family (biology), family of feathered coelurosaurian Theropoda, theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous period (geology), Period. The name Drom ...

therizinosaur Therizinosaurs (; once called segnosaurs) are an extinct group of large herbivorous theropod dinosaurs whose fossils have been mainly discovered from Cretaceous deposits in Asia and North America. Potential fragmentary remains have also been foun ...

s, and

tyrannosauroid Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinen ...

s) as well as

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 b ...

ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful l ...

s, and

iguanodontia Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively sm ...

ns. Several dinosaurian oospecies (egg fossils) have also described, including '' Himeoolithus'', '' Subtiliolithus'', '' Nipponoolithus'', and ''

Prismatoolithus ''Prismatoolithus'' is an oogenus of dinosaur egg from the Cretaceous (Hauterivian-Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stag ...

''. Although not specified as this formation in original descriptions, Sasayama Group have some other fossil fauna known, such as

eutherian Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distingu ...

'' Sasayamamylos'',

scincomorph Scincomorpha is an infraorder and clade of lizards including skinks (Scincidae) and their close relatives. These include the living families Cordylidae (girdled lizards), Gerrhosauridae (plated lizards), and Xantusiidae (night lizards), as well ...

'' Pachygenys'', two frogs '' Hyogobatrachus'' and '' Tambabatrachus''.

References

{{Taxonbar, from=Q127801335 Troodontidae Dinosaur genera Albian dinosaurs Fossil taxa described in 2024 Dinosaurs of Japan

Discovery and naming

Classification

Paleoecology

See also

References