''Eubrachiosaurus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

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 ...

stahleckeriid Stahleckeriidae is a family of dicynodont therapsids whose fossils are known from the Triassic of North America, South America, Asia and Africa. Classification Phylogeny Below is a cladogram A cladogram (from Greek ''clados'' "branch" and ...

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, typicall ...

known from the

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

( Carnian stage) of

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 ...

, 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 several ...

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 eithe ...

as well as a left

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

, and left

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

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 Chugwater is a town in Platte County, Wyoming, United States. As of the 2020 census, the town population was 175. History The Chugwater area, with its proximity to Fort Laramie, was visited by some of the earliest Western expeditions, includin ...

. ''Eubrachiosaurus browni'' was first described and named by Samuel Wendell Williston in

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 system. * ...

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 synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

s of '' Placerias hesternus'', 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 ''Ischigualastia'' is an extinct genus of large dicynodont therapsids that lived during the Late Carnian age and the Early Norian age of the Late Triassic Period. The genus was found in and named after the Ischigualasto Formation (Cancha de Boc ...

''. 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 Stahleckeriidae is a family of dicynodont therapsids whose fossils are known from the Triassic of North America, South America, Asia and Africa. Classification Phylogeny Below is a cladogram A cladogram (from Greek ''clados'' "branch" and ...

, most closely related to ''

Sangusaurus ''Sangusaurus'' is an extinct genus of large dicynodont synapsid with two recognized species: ''S. edentatus'' (the type species) and ''S. parringtonii''. ''Sangusaurus'' is named after the Sangu stream in eastern Zambia near to where it was firs ...

''. 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

synonymous A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

, but noted that on a strict

apomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

basis ''Brachybrachium brevipes'' must be considered a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

''.

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