''Caseosaurus'' ( ) is a dubious

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...

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 ...

that lived approximately 221.5 to 212

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...

during the latter part of the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

in what is now

Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...

, in North America. It was a small, lightly-built,

bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

, ground-dwelling

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...

, and could grow up to long.

Description

The genus ''Caseosaurus'', is known from specimen UMMP 8870, an isolated hip bone that measures nearly 141 mm. A 3D model of this specimen is available on th
University of Michigan Online Repository of Fossils
Size estimates suggest that ''Caseosaurus'' was at best long and weighed at most.

Discovery

The genus name ''Caseosaurus'', means "Case's lizard", and was named in the honor of the scientist who discovered it,

Ermine Cowles Case Ermine Cowles Case (1871–1953), invariably known as E.C. Case, was a prominent American paleontologist in the second generation that succeeded Othniel Charles Marsh and Edward Drinker Cope. A graduate of the University of Kansas, with a PhD ...

. 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 ...

suffix "-saurus" () means "lizard". The specific name ''crosbyensis'', is a Latinized rendering of Crosby County in Texas, the site of its discovery. ''Caseosaurus'' was described and named by A. P. Hunt, Spencer G. Lucas, Andrew B. Heckert, Robert M. Sullivan and Martin Lockley in

1998 1998 was designated as the ''International Year of the Ocean''. Events January * January 6 – The ''Lunar Prospector'' spacecraft is launched into orbit around the Moon, and later finds evidence for frozen water, in soil in permanently s ...

and the

type species In 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 species that contains the biological type specime ...

is ''Caseosaurus crosbyensis''.Hunt, A. P., Lucas, S. G., Heckert, A. B., Sullivan, R. M., and Lockley, M. G., 1998, Late Triassic Dinosaurs from the Western United States: Geobios, v. 31, n. 4, p. 511-531.

Classification

In 1998, Hunt ''et al.'', examined UMMP 8870, a partial hip bone ( ilium) that was assigned as a

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...

of the dinosaur ''

Chindesaurus ''Chindesaurus'' ( ) is an extinct genus of basal saurischian dinosaur from the Late Triassic (213-210 million years ago) of the southwestern United States. It is known from a single species, ''C. bryansmalli'', based on a partial skeleton recovere ...

'' and made it 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 sever ...

of a new dinosaur, ''Caseosaurus crosbyensis''. Irmis ''et al.'' concluded that an ilium, NMMNH P-35995 originally assigned by Heckert ''et al.'', in 2000 to the

silesaurid Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compri ...

'' Eucoelophysis'', strongly resembles the ''Caseosaurus'' holotype. Langer (2004) examined the ilium and reassigned it back to the genus ''

''. Other paleontologists also agree that this may be the same dinosaur as ''

'', which lived during the same period and geological region. However, in 2018 ''Caseosaurus'' was considered a valid species, as a relative of ''

Herrerasaurus ''Herrerasaurus'' is a genus of saurischian dinosaur from the Late Triassic period. This genus was one of the earliest dinosaurs from the fossil record. Its name means "Herrera's lizard", after the rancher who discovered the first specimen in ...

'' outside of the Dinosauria.

Distinguishing anatomical features

According to Hunt ''et al.'' (1998), ''Caseosaurus'' could be distinguished based on the following features: * a shallow brevis shelf is present on the ilium * a medial longitudinal ridge that is more ventrally placed * a transversely thinner postacetabular blade is present

Paleoecology

The only specimen of ''Caseosaurus'' was discovered in the

Tecovas Formation The Tecovas Formation is a geological formation in Texas.Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Triassic, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berk ...

of the

Dockum Group The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colora ...

, in sediments deposited during the Norian stage of the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

period, approximately 221.5 to 212 million years ago. ''Caseosauruss paleoenvironment included the archosaur ''

Tecovasaurus ''Tecovasaurus'' (te-KOH-va-SAWR-us) is an extinct Late Triassic amniote genus of unknown affinities, known only from teeth. It was initially described as a basal ornithischian dinosaur, subsequently reclassified as a member of the clade Archosa ...

'' and other early theropod dinosaurs, some of whom left bipedal tracks that were preserved.

References

External links

Texas Dinosaurs
from Texas A&M University {{Taxonbar, from=Q548002 Prehistoric saurischians Dinosaur genera Late Triassic dinosaurs of North America Triassic geology of Texas Taxa named by Spencer G. Lucas Taxa named by Robert M. Sullivan Taxa named by Martin Lockley Nomina dubia