A Molecular Phylogeny of Plesiorycteropus Reassigns the Extinct Mammalian Order ‘Bibymalagasia’

Madagascar is well known for its diverse fauna and flora, being home to many species not found anywhere else in the world. However, its biodiversity in the recent past included a range of extinct enigmatic fauna, such as elephant birds, giant lemurs and dwarfed hippopotami. The ‘Malagasy aardvark’ (Plesiorycteropus) has remained one of Madagascar’s least well-understood extinct species since its discovery in the 19th century. Initially considered a close relative of the aardvark (Orycteropus) within the order Tubulidentata, more recent morphological analyses challenged this placement on the grounds that the identifiably derived traits supporting this allocation were adaptations to digging rather than shared ancestry. Because the skeletal evidence showed many morphological traits diagnostic of different eutherian mammal orders, they could not be used to resolve its closest relatives. As a result, the genus was tentatively assigned its own taxonomic order ‘Bibymalagasia’, yet how this order relates to other eutherian mammal orders remains unclear despite numerous morphological investigations. This research presents the first known molecular sequence data for Plesiorycteropus, obtained from the bone protein collagen (I), which places the ‘Malagasy aardvark’ as more closely related to tenrecs than aardvarks. More specifically, Plesiorycteropus was recovered within the order Tenrecoidea (golden moles and tenrecs) within Afrotheria, suggesting that the taxonomic order ‘Bibymalagasia’ is obsolete. This research highlights the potential for collagen sequencing in investigating the phylogeny of extinct species as a viable alternative to ancient DNA (aDNA) sequencing, particularly in cases where aDNA cannot be recovered.马达加斯加以其多样的动植物群落闻名于世，境内孕育着诸多全球独有的特有物种。然而其近代生物多样性中曾包含一类已灭绝的神秘类群，例如象鸟、巨型狐猴以及矮河马。‘马达加斯加土豚’（*Plesiorycteropus*）自19世纪被发现以来，一直是马达加斯加最鲜为人知的灭绝物种之一。最初该物种被归为管齿目（Tubulidentata）中土豚属（*Orycteropus*）的近亲，然而后续的形态学研究对此分类地位提出了质疑——理由是支持该归类的可识别衍征实为适应掘土的趋同演化特征，而非源于共同祖先的共有性状。由于其骨骼化石展现出诸多可区分不同真兽类哺乳动物（eutherian mammal）目级类群的形态特征，无法仅凭这些特征确定其最近缘亲缘类群。因此，该属被暂时独立设立为专属分类目——‘比伯马达加斯加目（Bibymalagasia）’，但尽管开展了大量形态学研究，该目与其他真兽类哺乳动物目之间的演化关系仍不明朗。本研究首次获取了*Plesiorycteropus*的分子序列数据，该数据源自骨骼中的I型胶原蛋白（collagen I），分析结果表明‘马达加斯加土豚’与马岛猬的亲缘关系较与土豚更近。更具体地说，*Plesiorycteropus*被归入非洲兽总目（Afrotheria）下的马岛猬总科（Tenrecoidea，涵盖金鼹与马岛猬类群），这意味着‘比伯马达加斯加目’这一分类单元已不再适用。本研究证明，胶原蛋白测序可作为古DNA（ancient DNA, aDNA）测序的可行替代方案，在古DNA无法成功获取的情况下，其在灭绝物种系统发育研究中具备巨大应用潜力。