''Eubrachiosaurus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of stahleckeriid

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

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 a ...

(

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 227.3 ...

stage) of

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

, United States.

Description

''Eubrachiosaurus'' is known only from the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen FMNH UC 633, a partial left

scapula The scapula (: 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 either side ...

as well as a left

humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

, and left

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

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 ( )Locally "po-PO-zha" according to Don Pitcher, 2006, ''Moon Handbooks Wyoming,'' p. 26/ref>More ambiguous transcription of "po-po-zsha" at is a Triassic geologic Formation (geology), formation that outcrop, crops out in ...

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 Paleontology, paleontologist who was the first to propose that birds developed flight Origin of birds#Origin of bird flight, cursorially (by ...

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

junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

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''. 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 ''Lystrosa ...

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 precisely 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 a ...

, but noted that on a strict

apomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...

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 ...

''.

References

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