''Eubrachiosaurus'' is an extinct

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 ...

of stahleckeriid

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typic ...

known from 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. ...

(

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...

stage) of

Wyoming Wyoming () is a state in the 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 southwest, and Colorado to the s ...

, United States.

Description

''Eubrachiosaurus'' is known only from 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 ...

specimen FMNH UC 633, a partial left

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...

as well as a left humerus, and left pelvis which have been lost. It was collected at the Little Popo Agie River, near Lander, Fremont County from the

Popo Agie Formation The Popo Agie Formation is a Triassic geologic formation that crops out in western Wyoming, western Colorado, and Utah. It was deposited during the Late Triassic in fluvial (river) and lacustrine (lake) environments that existed across much of ...

of the Chugwater Group. ''Eubrachiosaurus browni'' was first described and named by

Samuel Wendell Williston Samuel Wendell Williston (July 10, 1852 – August 30, 1918) was an American educator, entomologist, and paleontologist who was the first to propose that birds developed flight cursorially (by running), rather than arboreally (by leaping from tr ...

1904 Events January * January 7 – The distress signal ''CQD'' is established, only to be replaced 2 years later by ''SOS''. * January 8 – The Blackstone Library is dedicated, marking the beginning of the Chicago Public Library syst ...

along with ''

Brachybrachium ''Eubrachiosaurus'' is an extinct genus of stahleckeriid dicynodont known from the Late Triassic (Carnian stage) of Wyoming, United States. Description ''Eubrachiosaurus'' is known only from the holotype specimen Field Museum of Natural Histor ...

brevipes''. Lucas and Hunt (1993) considered both taxa junior synonyms of ''

Placerias hesternus ''Placerias'' (meaning 'broad body') is an extinct genus of dicynodonts that lived during the Carnian to the Norian age of the Triassic Period (230–220 million years ago). ''Placerias'' belongs to a group of dicynodonts called Kannemeyeriiforme ...

'', which is known from the same formation, a position maintained in most subsequent studies. The synonymy of ''Eubrachiosaurus'' and ''Placerias'' was questioned by Long and Murry (1995) who noted that the ectepicondyle of ''Eubrachiosaurus'' was enlarged as in '' Ischigualastia''. All of Williston's dicynodont material from Popo Agie has been lost, apart from the partial left scapula of ''Eubrachiosaurus''. Kammerer ''et al.'' (2013) redescribed the available material and the missing elements were redescribed from photographs taken by Williston (1904), and suggested that ''Eubrachiosaurus'' is a valid member of the Stahleckeriinae, most closely related to '' Sangusaurus''. Kammerer ''et al.'' (2013) also noted that Williston (1904) described ''Brachybrachium'' on the basis of a fragmentary humerus from the upper Popo Agie beds, in "almost identically the same horizon" as ''Eubrachiosaurus''. The currently lost specimen was poorly preserved with much of the proximal and distal ends missing. It shares with the humerus of ''Eubrachiosaurus'' a nearly perpendicular angle between the edges of the deltopectoral crest. Furthermore, the traits on which basis Williston used to distinguish the two taxa are either known to vary intraspecifically in

kannemeyeriiform Kannemeyeriiformes is a group of large-bodied Triassic dicynodonts. As a clade, Kannemeyeriiformes has been defined to include the species ''Kannemeyeria simocephalus'' and all dicynodonts more closely related to it than to the species '' Lystro ...

s or were too badly preserved in ''Brachybrachium'' to display clear morphological differences from ''Eubrachiosaurus''. Thus, Kammerer ''et al.'' (2013) concluded the it is probable that these two taxa are synonym (taxonomy), synonymous, but noted that on a strict apomorphy basis ''Brachybrachium brevipes'' must be considered a ''nomen dubium''.

References

{{Portal bar, Paleontology Kannemeyeriiformes Carnian genera Late Triassic tetrapods of North America Taxa named by Samuel Wendell Williston Triassic synapsids of North America Fossils of the United States Paleontology in Wyoming Fossil taxa described in 1904 Anomodont genera