We provide detailed morphological description, including enamel microstructure, of the earliest known embrithopod mammals (Afrotheria, Paenungulata), Stylolophus minor and S. major, n. sp., recently discovered in the early Eocene of the Ouled Abdoun phosphate basin, Morocco. Stylolophus minor and S. major, n. sp., show close morphological affinity, and the enamel microstructure supports their congeneric status. Stylolophus major, which comes from an upper level (middle Ypresian) of the Ouled Abdoun phosphate series, has more derived features than S. minor in addition to a larger size. This argues that S. minor and S. major are chronospecies. This new mammal lineage recognized in the Ouled Abdoun phosphate series is characterized by a rapid size increase, as for the proboscideans and probably in correlation with early-middle Ypresian global climatic warming events. We investigated relationships of Stylolophus in a new cladistic analysis based on an extended and revised matrix that includes new enamel microstructural features studied in Stylolophus. Resulting MPTs recover 1) basal relationships of Stylolophus within the Embrithopoda; 2) sister-group relationship of the Embrithopoda to the crown Tethytheria (Proboscidea, Sirenia); and 3) the clades Tethytheria and Paenungulata. It supports in particular that the order Embrithopoda is a basal tethytherian offshoot that rapidly evolved and specialized in parallel to the splitting and early evolution of extant tethytherian orders. Stylolophus shows that the ancestral embrithopod morphotype was already well specialized in the early Eocene and quite distinctive with respect to other paenungulates (e.g., hyperdilambdodonty, lingual hypoconulid, cristid obliqua very lingual on the trigonid, small and lingual hypoconulid lobe on M3, large paranasal sinuses, concave palate), even with respect to their earliest representatives. Stylolophus minor was larger than the contemporary proboscidean Phosphatherium escuilliei. Together with the stem tethytherian relationship of the Embrithopoda, it supports an old origin of the order, at least early in the Paleocene. This relationship is also most consistent with the evolution of the embrithopod hyperdilambdodont pattern from the dilambdodont and selenodont ancestral morphotype of the paenungulates, which is known in early hyracoids but not in proboscideans and sirenians, which have reduced the ectoloph. The most specialized embrithopods evolved hyperdilambdodonty in a pseudolophodont state in parallel to the true lophodonty of crown tethytherians. The Ouled Abdoun embrithopods further help indeed to show that the early Tertiary herbivorous niches of the African island favored convergent evolution of the folivorous diet in several paenungulate and tethytherian clades. At higher scale, convergence of African and Laurasian “ungulates” is supported by enamel microstructure of Stylolophus. The early and basalmost embrithopods S. minor and S. major, n. sp., are new evidence of the Arabo-African origin of the order.

中文翻译：

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摩洛哥早始新世最早的胚足类哺乳动物（Afrotheria、Tethytheria）：解剖学、系统学和系统发育意义

我们提供了最早的已知胚足类哺乳动物（Afrotheria、Paenungulata）、Stylolophus minor 和 S. major，n. 的详细形态描述，包括釉质微观结构。sp.，最近在摩洛哥 Ouled Abdoun 磷酸盐盆地的始新世早期发现。Stylolophus minor 和 S. major，n。sp.，显示出密切的形态学亲和力，并且牙釉质微观结构支持它们的同类状态。Stylolophus Major 来自 Ouled Abdoun 磷酸盐系列的上层（中伊普鲁西亚），除了更大的尺寸外，还具有比 S. minor 更多的派生特征。这认为 S. minor 和 S. major 是时间种。在 Ouled Abdoun 磷酸盐系列中发现的这种新哺乳动物谱系的特点是体型迅速增加，至于长鼻类，可能与伊普勒西亚早期中期全球气候变暖事件有关。我们在基于扩展和修订矩阵的新分支分析中调查了 Stylolophus 的关系，该矩阵包括在 Stylolophus 中研究的新釉质显微结构特征。由此产生的 MPT 恢复了 1) 在 Embrithopoda 中 Stylolophus 的基础关系；2) Embrithopoda 与冠 Tethytheria (Proboscidea, Sirenia) 的姐妹群关系；和 3) 进化枝 Tethytheria 和 Paenungulata。它特别支持 Embrithopoda 目是基础 tethytherian 分支，其快速进化和特化，与现存 tethytherian 目的分裂和早期进化平行。Stylolophus 表明，祖先的胚足类动物的形态类型在始新世早期已经很好地特化，并且与其他有齿类动物（例如，超二尖牙、舌下锥体、三棱上非常舌的嵴斜齿、M3 上的小和舌下锥体叶、大鼻窦） ，凹上颚），即使是关于他们最早的代表。Stylolophus minor 比同时代的长鼻类 Phosphatherium escuilliei 大。连同 Embrithopoda 的茎干 tethytherian 关系，它支持该目的一个古老起源，至少在古新世早期。这种关系也最符合 embrithopod hyperdilambdont 模式从 paenungulates 的 dilambdodon 和 selenodont 祖先形态的进化，这在早期 hyracoids 中是已知的，但在 proboscideans 和 Sirenians 中没有，它们减少了 ectoloph。最特化的胚足类动物进化为假齿齿兽状态下的超二棱齿齿兽，与真正的冠齿兽齿齿兽平行。Ouled Abdoun embrithopods 确实进一步帮助表明，非洲岛屿的早期第三纪食草生态位有利于在几个paenungulate 和tethytherian 进化枝中食叶饮食的趋同进化。在更高的尺度上，柱形目的釉质微结构支持了非洲和劳亚“有蹄类动物”的融合。早期和最基部的胚足类 S. minor 和 S. major，n. sp.，是该命令阿拉伯-非洲起源的新证据。最特化的胚足类动物进化为假齿齿兽状态下的超二棱齿齿兽，与真正的冠齿兽齿齿兽平行。Ouled Abdoun embrithopods 确实进一步有助于表明非洲岛屿的早期第三纪食草生态位有利于在几个paenungulate 和tethytherian 进化枝中食叶饮食的趋同进化。在更高的尺度上，柱形目的釉质微结构支持了非洲和劳亚“有蹄类动物”的融合。早期和最基部的胚足类 S. minor 和 S. major，n. sp.，是该命令阿拉伯-非洲起源的新证据。最特化的胚足类动物进化为假齿齿兽状态下的超二棱齿齿兽，与真正的冠齿兽齿齿兽平行。Ouled Abdoun embrithopods 确实进一步帮助表明，非洲岛屿的早期第三纪食草生态位有利于在几个paenungulate 和tethytherian 进化枝中食叶饮食的趋同进化。在更高的尺度上，柱形目的釉质微结构支持了非洲和劳亚“有蹄类动物”的融合。早期和最基部的胚足类 S. minor 和 S. major，n. sp.，是该命令阿拉伯-非洲起源的新证据。Ouled Abdoun embrithopods 确实进一步有助于表明非洲岛屿的早期第三纪食草生态位有利于在几个paenungulate 和tethytherian 进化枝中食叶饮食的趋同进化。在更高的尺度上，柱形目的釉质微结构支持了非洲和劳亚“有蹄类动物”的融合。早期和最基部的胚足类 S. minor 和 S. major，n. sp.，是该命令阿拉伯-非洲起源的新证据。Ouled Abdoun embrithopods 确实进一步帮助表明，非洲岛屿的早期第三纪食草生态位有利于在几个paenungulate 和tethytherian 进化枝中食叶饮食的趋同进化。在更高的尺度上，柱形目的釉质微结构支持了非洲和劳亚“有蹄类动物”的融合。早期和最基部的胚足类 S. minor 和 S. major，n. sp.，是该命令阿拉伯-非洲起源的新证据。