Data from: On the existence of non-microbiotherian Australidelphian marsupials (Diprotodontia) in the Eocene of Patagonia

A diverse assemblage of extinct mammals of early–middle Eocene age (Ypresian–Lutetian boundary) come from the Patagonian localities of La Barda and Laguna Fría around Paso del Sapo in northwestern Chubut Province (Argentina). Metatherians are well represented, mostly by dental remains of ‘Didelphimorphia’, Paucituberculata, Sparassodonta, Microbiotheria, and Polydolopimorphia. Here we analyse three calcanea and one astragalus referable to the same, indeterminate taxon, from La Barda, showing the fusion of their ectal and sustentacular facets. This facet arrangement characterizes the Australidelphia, a marsupial clade represented by Microbiotheria from South America and Antarctica, plus all Australasian lineages. Other australidelphian features shown by these tarsals include: in the calcanea, a reduced peroneal process and a tripartite cuboid facet; in the astragalus, a round, very small astragalar head in relation to the body; a convex trochlea with a half for the tibia and half, in slightly lower position, for the fibula. Their size and other anatomical features suggest that the new tarsals cannot be referred to the Microbiotheria. Phylogenetic analysis suggests that the La Barda taxon lies within the Australidelphia, and that it is either closely related or belongs to, the Diprotodontia. The existence of advanced australidelphians in Patagonia adds further evidence of the close relationship between Patagonia, Antarctica, and Australia during the Late Cretaceous – early Palaeogene.产自阿根廷丘布特省西北部帕索德尔萨波（Paso del Sapo）周边拉巴尔达（La Barda）与拉古纳弗里亚（Laguna Fría）两处巴塔哥尼亚产地的灭绝哺乳动物化石组合类群多样，其时代为始新世早-中期（伊普雷斯阶-吕特阶界线）。其中后兽类（Metatherians）化石记录丰富，主要以负鼠目（Didelphimorphia）、少结齿目（Paucituberculata）、鬣齿有袋目（Sparassodonta）、微兽目（Microbiotheria）以及多瘤齿有袋目（Polydolopimorphia）的牙齿化石为代表。本次研究针对拉巴尔达产地出土的3件跟骨（calcaneum，复数为calcanea）与1件距骨（astragalus）展开分析，这些化石均隶属于同一未定类群，其特征为外踝面与载距突面发生融合。这种关节面组合方式是澳洲有袋类支系（Australidelphia）的典型特征：该有袋类演化支涵盖产自南美洲与南极洲的微兽目，以及所有澳大拉西亚演化支系。这批跗骨还展现出其他澳洲有袋类的鉴别特征：在跟骨上可见退化的腓骨肌突（peroneal process）与三分状骰骨关节面（cuboid facet）；在距骨上，其距骨头（astragalar head）呈圆形且相较于距骨体尺寸极小；距骨滑车（trochlea）呈凸面形态，其中一半与胫骨（tibia）相关节，另一半位置稍低，与腓骨（fibula）相关节。通过化石尺寸与其他解剖学特征判断，这批新发现的跗骨无法归入微兽目。系统发育分析结果显示，拉巴尔达产地的该未定类群隶属于澳洲有袋类支系，且与双门齿目（Diprotodontia）亲缘关系极近，或可归入该目。巴塔哥尼亚地区存在高等澳洲有袋类类群的发现，进一步为晚白垩世-古近纪早期巴塔哥尼亚、南极洲与澳大利亚之间的紧密生物地理联系提供了新证据。