Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity, Berlin, Germany.
PLoS One. 2013 May 31;8(5):e64203. doi: 10.1371/journal.pone.0064203. Print 2013.
The large dicynodont Eubrachiosaurus browni from the Upper Triassic Popo Agie Formation of Wyoming is redescribed. Eubrachiosaurus is a valid taxon that differs from Placerias hesternus, with which it was previously synonymized, by greater anteroposterior expansion of the scapula dorsally and a very large, nearly rectangular humeral ectepicondyle with a broad supinator process. Inclusion of Eubrachiosaurus in a revised phylogenetic analysis of anomodont therapsids indicates that it is a stahleckeriid closely related to the South American genera Ischigualastia and Jachaleria. The recognition of Eubrachiosaurus as a distinct lineage of North American dicynodonts, combined with other recent discoveries in the eastern USA and Europe, alters our perception of Late Triassic dicynodont diversity in the northern hemisphere. Rather than being isolated relicts in previously therapsid-dominated regions, Late Triassic stahleckeriid dicynodonts were continuing to disperse and diversify, even in areas like western North America that were otherwise uninhabited by coeval therapsids (i.e., cynodonts).
现重新描述产自怀俄明州上三叠统波颇安吉组的大型二齿兽类真双齿兽布朗氏（Eubrachiosaurus browni）。真双齿兽是一个有效分类单元，与之前被归为同物异名的 Placerias hesternus 不同，其肩胛骨背侧的前后扩张程度更大，肱骨外髁非常大，几乎呈矩形，有宽阔的旋后肌突。将真双齿兽纳入改进后的异齿兽类系统发育分析表明，它是与南美洲的 Ischigualastia 和 Jachaleria 属密切相关的 Stahleckeriidae 成员。真双齿兽作为北美二齿兽类的一个独特谱系得到确认，再加上美国东部和欧洲的其他近期发现，改变了我们对北半球晚三叠世二齿兽类多样性的认识。晚三叠世的 Stahleckeriidae 二齿兽类并没有像之前的兽孔类那样成为孤立的残余种，而是继续扩散和多样化，甚至在北美西部等地，尽管没有同时代的兽孔类（即犬齿兽类）居住，但它们仍在这些地区生存。
