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 FMNH UC 633, a partial left
scapula 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 of the
Chugwater Group.
Eubrachiosaurus browni was first described and named by Samuel Wendell Williston in 1904 along with
Brachybrachium brevipes. Lucas and Hunt (1993) considered both taxa
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.
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]
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 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, but noted that on a strict apomorphy basis Brachybrachium brevipes must be considered a nomen dubium.[
]
