CR2P, Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements; UMR 7207, CNRS, MNHN, UPMC, Sorbonne Universités Muséum National d'Histoire Naturelle, Département Origines et Evolution, CP 38, 8 Rue Buffon, 75005 Paris, France.
CR2P, Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements; UMR 7207, CNRS, MNHN, UPMC, Sorbonne Universités Muséum National d'Histoire Naturelle, Département Origines et Evolution, CP 38, 8 Rue Buffon, 75005 Paris, France.
Curr Biol. 2018 Jul 9;28(13):2167-2173.e2. doi: 10.1016/j.cub.2018.05.032. Epub 2018 Jun 28.
Modern mammals rapidly evolved in the early Cenozoic in all continental provinces, including in Africa, with one of the first placental branches, the Afrotheria [1, 2]. Afrotherian evolution is at the origin of the major radiation of African ungulate-like mammals, including extant hyrax, elephant, and sea cow orders, which all belong to the Paenungulata. The paenungulate radiation also includes the extinct order Embrithopoda of uncertain interordinal relationships, which is best known for the giant and strangely specialized Oligocene genus Arsinoitherium. The Ouled Abdoun basin, Morocco, yielded exceptional Paleocene-Eocene fossils documenting the early paenungulate evolution [3-8]. Here we report two new small Ypresian species, Stylolophus minor n.g., n.sp. and cf. Stylolophus sp., which are the earliest and most primitive embrithopods. The cladistic analysis relates the Embrithopoda to crown paenungulates as the stem-group of the Tethytheria, which makes crown tethytherians restricted to extant elephant and sea cow orders. The Embrithopoda is therefore an early tethytherian offshoot predating the elephant and sea cow divergence. The resulting phylogeny supports a strictly African early radiation of the paenungulates excluding the Phenacolophidae and Anthracobunia. It sustains an at least early Paleocene African origin of the Embrithopoda. The unique tooth pattern of the embrithopods (hyperdilambdodont and pseudolophodont molars) is resolved as evolving early and directly from the dilambdodont (W-shaped labial molar crests) ancestral paenungulate morphotype. The specialized upper molar morphology with two transverse crests is convergent and non-homologous in embrithopods and crown Tethytheria. These convergences for specialized folivorous diet were driven by free herbivorous African niches in the early Paleogene.
现代哺乳动物在整个大陆省份（包括非洲）的新生代早期迅速进化，其中最早的胎盘分支之一是 Afrotheria [1, 2]。 Afrotherian 的进化起源于非洲有蹄类哺乳动物的主要辐射，包括现存的蹄兔目、象目和海牛目，它们都属于 Paenungulata。 Paenungulata 的辐射还包括灭绝的不确定目间关系的 Embrithopoda 目，它以奇异特化的渐新世属 Arsinoitherium 而闻名。摩洛哥的 Ouled Abdoun 盆地提供了特殊的古新世至始新世化石，记录了早期 paenungulate 的进化[3-8]。在这里，我们报告了两个新的小型 Ypresian 物种，Stylolophus minor n.g., n.sp.和 cf. Stylolophus sp.，它们是最早和最原始的 embrithopods。系统发育分析将 Embrithopoda 与冠 paenungulates 相关联，作为 Tethytheria 的茎群，这使得冠 tethytherians 仅限于现存的象目和海牛目。因此，Embrithopoda 是一种早期的 tethytherian 分支，早于象目和海牛目的分化。由此产生的系统发育支持了 paenungulates 的严格非洲早期辐射，排除了 Phenacolophidae 和 Anthracobunia。它支持 Embrithopoda 的至少早期古新世非洲起源。 embrithopods 的独特牙齿模式（超 Dilambdodont 和假 Lophodont 臼齿）被解析为从 Dilambdodont（W 形唇侧臼齿嵴）祖型 paenungulate 形态型早期直接进化而来。具有两个横向嵴的特化上臼齿形态在 embrithopods 和冠 Tethytheria 中是趋同的，并且不是同源的。这些专门的食草饮食趋同是由早期古近纪非洲自由的食草生态位驱动的。
