Caseosaurus (/ˌkeɪziːoʊˈsɔːrəs/ KAY-zee-o-SAWR-əs) is a dubious genus of herrerasaurid theropod dinosaur that lived approximately 235 to 228 million years ago during the latter part of the Triassic Period in what is now Texas, in North America. Caseosaurus was a small, lightly-built, bipedal, ground-dwelling carnivore, that could grow up to 2 m (6.6 ft) long.
|Holotype ilium in outer and inner view|
Hunt et al., 1998
Hunt et al., 1998
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 the University of Michigan Online Repository of Fossils. Size estimates suggest that Caseosaurus was at best 2 m (6.6 ft) long and weighed 50 kilograms (110.2 pounds) at most.
The genus name Caseosaurus, means "Case's lizard", and was named in the honor of the scientist who discovered it, Ermine Cowles Case. The Greek suffix "-saurus" (σαυρος) 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 and the type species is Caseosaurus crosbyensis.
In 1998, Hunt et al., examined UMMP 8870, a partial hip bone (ilium) that was assigned as a paratype of the dinosaur Chindesaurus and made it the holotype 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 dinosaur Eucoelophysis, strongly resembles the Caseosaurus holotype. Caseosaurus has also been classified as a relative of Herrerasaurus. Langer (2004) examined the ilium and reassigned it back to the genus Chindesaurus. Other paleontologists also agree that this may be the same dinosaur as Chindesaurus, which lived during the same period and geological region.
According to Hunt et al. (1998), Caseosaurus could be distinguished based on the following features:
The only specimen of Caseosaurus was discovered in the Tecovas Formation of the Dockum Group in Texas, in sediments deposited during the Carnian stage of the Late Triassic period, approximately 235 to 228 million years ago. Caseosaurus's paleoenvironment included the archosaur Tecovasaurus and other early theropod dinosaurs, some of whom left bipedal tracks that were preserved.
The Anchisauria were a clade of sauropodomorph dinosaurs that lived during the Late Triassic and Early Jurassic. The name Anchisauria was first used by Galton and Upchurch in the second edition of The Dinosauria. Galton and Upchurch assigned two families of dinosaurs to the Anchisauria: the Anchisauridae and the Melanorosauridae. The more common prosauropods Plateosaurus and Massospondylus were placed in the sister clade Plateosauria.
However, recent research indicates that Anchisaurus is closer to sauropods than traditional prosauropods; thus, Anchisauria would also include Sauropoda.The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Chindesaurus
Chindesaurus ( CHIN-di-SAWR-əs) is a genus of herrerasaurid dinosaur that lived approximately 235-210 million years ago during the latter part of the Triassic Period in what is now the Southwestern United States. Chindesaurus was a small, bipedal carnivore that could grow up to 2 to 2.3 m (6.6 to 7.5 ft) long.Dinosauriformes
Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.Herrerasauridae
Herrerasauridae is a family of carnivorous basal saurischian dinosaurs. They are among the oldest known dinosaurs, first appearing in the fossil record around 233.23 million years ago (Late Triassic), before becoming extinct by the end of the Triassic period. Herrerasaurids were relatively small-sized dinosaurs, normally not more than 4 metres (13 ft) long. The best known representatives of this group are from South America (Brazil, Argentina), where they were first discovered in the 1960s. A nearly complete skeleton of Herrerasaurus ischigulastensis was discovered in the Ischigualasto Formation in San Juan, Argentina, in 1988. Less complete herrerasaurids have been found in North America, and they may have inhabited other continents as well.
Herrerasaurid anatomy is unusual and specialized, and they are not considered to be ancestral to any later dinosaur group. They only superficially resemble theropods and often present a mixture of very primitive and derived traits. The acetabulum is only partly open, and there are only two sacral vertebrae, the lowest number among dinosaurs. The pubic bone has a derived structure, being rotated somewhat posteriorly and folded to create a superficially tetanuran-like terminal expansion, especially prominent in H. ischigulastensis. The hand is primitive in having five metacarpals and the third finger longer than the second, but resembles those of theropods in having only three long fingers, with curved claws. Herrerasaurids also have a hinged mandible, which is also found in theropods.Jeholosauridae
Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Melanorosauridae
The Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder "Prosauropoda": the Anchisauridae, the Plateosauridae, the Thecodontosauridae, and the Melanorosauridae. Since then, these families have undergone numerous revisions. Galton and Upchurch (2004) considered Camelotia, Lessemsaurus, and Melanorosaurus members of the family Melanorosauridae. A more recent study by Yates (2007) indicates that the melanorosaurids were instead early sauropods.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Raeticodactylidae
Raeticodactylidae is a family of eudimorphodontoid eopterosaurian pterosaurs that lived in Switzerland during the Late Triassic. The family includes Caviramus, and the type genus Raeticodactylus, which are both known from the Kössen Formation, around 205 mya. Raeticodactylidae was first used in 2014 by Andres et al., as a group of all pterosaurs closer to Raeticodactylus than Eudimorphodon. The following phylogenetic analysis follows the topology of Andres et al. (2014).Riojasauridae
Riojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus. Sites containing Riojasauridae include the Lower Elliot Formation of Orange Free State, South Africa (where fossils of Eucnemesaurus have been found), and Ischigualasto, in La Rioja Province, Argentina ( where fossils of Riojasaurus have been recovered).Saltopus
Saltopus ("hopping foot") is a genus of very small bipedal dinosauriform containing the single species S. elginensis from the late Triassic period of Scotland. It is one of the most famous Elgin Reptiles.Tecovas Formation
The Tecovas Formation is a geological formation in Texas.Xixiposaurus
Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.