''Sasayamagnomus'' (meaning "Gnome from Sasayama") is a genus of

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 ...

dinosaur from the Early Cretaceous (

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 of Hyogo prefecture,

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 ...

. The genus contains a single species, ''S. saegusai''. Type specimen is estimated to reach long, although this specimen is not fully grown.

Discovery and naming

''Sasayamagnomus'' was found at the Miyada microvertebrate site in Tamba-Sasayama city, Hyogo Prefecture. It is known from 17 assorted cranial bones, the right coracoid and a left tibia. The presence of two right nasals in the material suggests that at least two individuals were represented. Before its formal description, it had been announced in a conference abstract in 2023. The

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 ...

is specimen MNHAH D1-060516, and it was formally described as a new genus and species of neoceratopsian in 2024. The generic name ''Sasayamagnomus'' is named after the Sasayama Basin, from where the bones were collected, and the Latin word for gnome, ''gnomus.'' 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 ...

''saegusai'' honors the late Dr. Haruo Saegusa, who was the leader in dinosaur excavation in the Tamba area, and was a significant contributor to vertebrate paleontology in the Hyogo Prefecture.

Classification

In their

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

, Tanaka et al. (2024) recovered ''Sasayamagnomus'' 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 ...

to '' Aquilops'' in a basal

neoceratopsia 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 ...

n clade also containing ''

Auroraceratops ''Auroraceratops'', meaning "dawn horned face", is a genus of bipedal basal neoceratopsian dinosaur, from the Early Cretaceous (Aptian age) of north central China. The etymology of the generic name refers to its status as an early ceratopsian a ...

''. 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

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

age from the end of 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 ...

. 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. 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 ...

s, therizinosaurs, 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 ...

''. 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 ...

'', the titanosauriform sauropod '' Tambatitanis'', and the

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 '' Hypnovenator'' are also known from the formation. 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 '' Pachygenys'', two frogs '' Hyogobatrachus'' and '' Tambabatrachus''.

References

{{Taxonbar, from=Q130222784 Ceratopsia Dinosaur genera Aptian dinosaurs Fossil taxa described in 2024 Dinosaurs of Japan

Discovery and naming

Classification

Paleoecology

See also

References