''Fukuivenator'' ("hunter of

Fukui Prefecture is a Prefectures of Japan, prefecture of Japan located in the Chūbu region of Honshū. Fukui Prefecture has a population of 737,229 (1 January 2025) and has a geographic area of 4,190 Square kilometre, km2 (1,617 sq mi). Fukui Prefecture border ...

") is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

maniraptoran Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to '' Ornithomimus velox''. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae ...

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

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 ...

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 ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

Discovery and naming

The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''Fukuivenator paradoxus'' was named and described in 2016 by Yoichi Azuma, Xu Xing, Masateru Shibata, Soichiro Kawabe, Kazunori Miyata and Takuya Imai. The generic name combines a reference to the Fukui prefecture with

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 ...

''venator'', "hunter". 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 ...

refers to the paradoxical combination of traits shown by the species. The rocks in which the skeleton of ''Fukuivenator'',

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 ...

FPDM-V8461, was found in August 2007 belong to the

Kitadani Formation The Kitadani Formation ( ''Kitadani-sō'') is a unit of Lower Cretaceous sedimentary rock which crops out near the city of Katsuyama in Fukui Prefecture, Japan, and it is the primary source of Cretaceous-aged non-marine vertebrate fossils in Jap ...

, which is probably of

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 125.77 Ma (million years ago) and 121.4 ± 1.0 Ma (Historically, this stage was placed at 129.4 million to approximately 125 million years ago) It is a ...

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

age. Radiometric dating of nearby rock units has given this formation an estimated age of somewhere between 127 and 115 million years old. The holotype consists of a partial skeleton with skull. The skeleton of ''F. paradoxus'' is currently the most complete non-avian dinosaur fossil found in Japan. The remains, including about 160 bones and bone fragments, were not found in articulation and recovered from an area of .

Description

''Fukuivenator'' had an estimated length of and an estimated weight of . Distinctive traits include spatulate teeth in the front

praemaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals has ...

e, pointed, recurved and unserrated teeth in the maxillae and a long neck with elongated neck vertebrae.

Classification

The anatomy of ''Fukuivenator'' shows a unique combination of primitive and advanced

coelurosauria Coelurosauria (; from Greek, meaning "hollow-tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyra ...

n features. A

phylogenetic analysis 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 data ...

performed by the research team that described ''Fukuivenator'' found it to be a primitive member of the group

Maniraptoriformes Coelurosauria (; from Greek, meaning "hollow-tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyra ...

, in an unresolved position equally closely related to

ornithomimosaurs Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period (geology), Period of Laurasia (now Asia ...

maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae, ...

ns, and ''

Ornitholestes ''Ornitholestes'' (meaning "bird robber") is a small theropod dinosaur of the late Jurassic ( Brushy Basin Member of the Morrison Formation, middle Kimmeridgian age, about 154 million years agoTurner, C.E. and Peterson, F., (1999). "Biostratigrap ...

''. Several similarities with the

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

were explained as a case of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

.Azuma, Y., Xu X., Shibata, M., Kawabe, S., Miyata, K., and Imai, T. 2016. "A bizarre theropod from the Early Cretaceous of Japan highlighting mosaic evolution among coelurosaurians". ''Scientific Reports'', 6(20478). A 2021 study determined it a basal member of the

therizinosaurs 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 ...

, as shown below: Another enigmatic maniraptoran, ''

Migmanychion ''Migmanychion'' (meaning "claw mixture") is an extinct genus of maniraptoran theropod dinosaur from the Early Cretaceous Longjiang Formation of China. The genus contains a single species, ''M. laiyang'', known from an incomplete left forelimb ...

'', is supported as the closest taxon to ''Fukuivenator'' based on phylogenetic analyses:

Paleobiology

Diet

Because of the long neck and the

heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. Human dentition is heterodont and diphyodont as an example. In vertebrates, heterodont pertains to animals wher ...

unserrated teeth, the probably foremost of which had flattened outer ends, the describing authors suggested that ''Fukuivenator'' was no longer a pure carnivore but had adapted itself to a herbivorous or at least

omnivorous An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...

diet.

References