Data from: Patagonian Eocene Archaeopithecidae Ameghino, 1897 (Notoungulata): systematic revision, phylogeny and biostratigraphy

The Archaeopithecidae is a very poorly known group of native ungulates from the Eocene of Patagonia (Argentina), whose alpha taxonomy has remained obscure since Ameghino’s times. It is traditionally considered as a family representative of the Casamayoran (middle Eocene) South American Land Mammal Age and it is thought to be morphologically close to the notopithecids. After studying more than 200 specimens from several institutions, including all the type specimens, a taxonomic overestimation is established. Out of the six species considered originally as archaeopithecids, Archaeopithecus rogeri is here recognized as the only valid name and species; subsequent synonymies are proposed and previous taxonomic hypotheses discarded. This exhaustive revision has permitted improving the knowledge of A. rogeri and, for the first time, it has revealed many craniodental characters which allow amending its diagnosis and differentiating this taxon from other Eocene notoungulates. Archaeopithecus rogeri is a small-sized taxon characterized by its complete and rooted dentition, which is relatively higher than that of other contemporaneous short-crowned notoungulates and shows ontogenetic variation in size and morphology. The body mass range of A. rogeri (1.4–2.5 kg) is comparable to those of notopithecids and some small hegetotheriids. The phylogenetic analysis shows A. rogeri is not directly related to any family within Notoungulata, appearing into a polytomy, as a basal taxon of typotherians. The biochronological range of A. rogeri is adjusted to Vacan (middle Eocene) through the Barrancan subages (late middle Eocene); older (Riochican, late early Eocene) and younger (Mustersan, late Eocene) records remain to be confirmed.

古蹄兔科（Archaeopithecidae）是一类鲜为人知的巴塔哥尼亚（阿根廷）始新世本土有蹄类类群，自阿梅吉诺时代以来，其基础分类学（alpha taxonomy）研究始终模糊不清。传统上，该类群被视为卡萨马约兰期（中始新世）南美陆栖哺乳动物时代的代表性类群，且被认为在形态上与北柱兽科（Notopithecidae）类群相近。研究团队对来自多家机构的200余件标本（含全部模式标本）开展研究后，证实该类群存在分类学高估问题：原被归入古蹄兔科的6个物种中，仅罗杰古蹄兔（Archaeopithecus rogeri）为该科下唯一有效属种；其余原物种均被认定为同物异名，此前的各类分类学假说均被摒弃。此次全面修订不仅深化了学界对罗杰古蹄兔的认知，还首次揭示了大量颅齿特征，据此可修正其分类鉴别特征，并将该类群与其他始新世南方有蹄类（Notoungulata）区分开来。罗杰古蹄兔为小型类群，其完整且具齿根的齿列相较于同期其他短齿型南方有蹄类相对更高，且在体型与形态上存在个体发育变异。该物种的体重范围为1.4至2.5千克，与北柱兽科及部分小型赫氏柱兽科（Hegetotheriidae）类群相当。系统发育分析显示，罗杰古蹄兔与南方有蹄目内的任何类群均无直接亲缘关系，以基部类群的身份归入型兽亚目（Typotheria）的多歧支中。其生物年代分布范围被修订为覆盖瓦坎期（中始新世）至巴兰卡亚期（中始新世晚期）；此前报道的更早（里奥奇坎期，早始新世晚期）与更晚（穆斯特桑期，始新世晚期）的记录仍有待证实。