Orodrominae is a

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

of thescelosaurid

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 ...

known from the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

and

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

Distribution

Orodromines were a mostly

n based group with

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s from Canada and United States only. '' Albertadromeus'', as its name suggests, is only from the upper (later) part of the Oldman Formation in the Belly River Group of

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

, Canada. '' Orodromeus'', the type

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 ...

, was widespread through

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

. Its

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 ...

was found at the

Egg Mountain The Two Medicine Formation is a geological formation, or rock body, in northwestern Montana and southern Alberta that was deposited between and (million years ago), during Campanian (Late Cretaceous) time. It crops out to the east of the Rocky M ...

in the

Two Medicine Formation The Two Medicine Formation is a geological formation, or rock body, in northwestern Montana and southern Alberta that was deposited between and (million years ago), during Campanian (Late Cretaceous) time. It crops out to the east of the Rocky M ...

. ''

Oryctodromeus ''Oryctodromeus'' (meaning "digging runner") was a genus of small orodromine thescelosaurid dinosaur. Fossils are known from the Late Cretaceous Blackleaf Formation of southwestern Montana and the Wayan Formation of southeastern Idaho, USA, bot ...

'' fossils were found in the

Lima Peaks Lima ( ; ), originally founded as Ciudad de Los Reyes (City of The Kings) is the capital and the largest city of Peru. It is located in the valleys of the Chillón, Rímac and Lurín Rivers, in the desert zone of the central coastal part of th ...

section of the

Blackleaf Formation The Blackleaf Formation is a geologic formation in Montana. It preserves fossils dating back to the Albian to Cenomanian stages of the Cretaceous period.Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

. '' Zephyrosaurus'', the most widespread genus, lived in southern

and northern

Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...

. The locality of its

is the

Wolf Creek Canyon The wolf (''Canis lupus''; : wolves), also known as the gray wolf or grey wolf, is a large canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, and gray wolves, as popularly u ...

, which is a sandstone in the Cloverly Formation.

Age

Orodromines are widespread throughout time, starting in the

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

and ending in the Campanian. The earliest fossils are of '' Zephyrosaurus'' and are from the

(113 Ma). After a 13 million year gap in the fossil record, fossils of the less common ''

'' date to about 95 Ma in the

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

. The next chronological fossils are from 76.5 Ma and belong to '' Albertadromeus''. The latest orodromine fossils in the fossil record belong to the type genus, '' Orodromeus'', and date to 75 Ma.

Paleoecology

All orodromines lived the lifestyle of a ground dwelling herbivore. ''

'' burrows have been discovered. '' Orodromeus'' and '' Zephyrosaurus'' also probably lived in burrows.

Classification

Orodrominae is the sister taxon of

Thescelosaurinae Thescelosaurinae is a subfamily of thescelosaurid dinosaurs from the Early Cretaceous of Asia and the Late Cretaceous of North America. Distribution The distribution of Thescelosaurinae is quite large. They are widespread through United States a ...

. Its parent taxon is Thescelosauridae (Brown ''et al'', 2013).

Phylogeny

Prior to the description of Orodrominae, the genera now assigned to the subfamily were often considered part of Hypsilophodontidae. Hypsilophodontidae is now considered obsolete, and its former members have been considered to form a paraphyletic assemblage of basal euornithopods.Horner, J. and Weishampel, D. (1988), "Acomparative embryological study of two ornithischian dinosaurs". ''Nature'' (London), 332(No. 6161): 256-257 (1988) The cladogram below is based on a phylogenetic analysis by Brown ''et al.'', 2013. More recent analyses recover a slightly different topology Barta, Daniel E., and Mark A. Norell. "The osteology of Haya griva (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia." Bulletin of the American Museum of Natural History 445.1 (2021): 1-112.

References

{{Taxonbar, from=Q13965583 Cretaceous dinosaurs