Department of Integrative Anatomical Sciences, University of Southern California, Los Angeles, CA, USA.
Committee on Evolutionary Biology, The University of Chicago, Chicago, IL, USA.
Nature. 2018 Jun;558(7708):108-112. doi: 10.1038/s41586-018-0126-y. Epub 2018 May 23.
Haramiyida was a successful clade of mammaliaforms, spanning the Late Triassic period to at least the Late Jurassic period, but their fossils are scant outside Eurasia and Cretaceous records are controversial. Here we report, to our knowledge, the first cranium of a large haramiyidan from the basal Cretaceous of North America. This cranium possesses an amalgam of stem mammaliaform plesiomorphies and crown mammalian apomorphies. Moreover, it shows dental traits that are diagnostic of isolated teeth of supposed multituberculate affinities from the Cretaceous of Morocco, which have been assigned to the enigmatic 'Hahnodontidae'. Exceptional preservation of this specimen also provides insights into the evolution of the ancestral mammalian brain. We demonstrate the haramiyidan affinities of Gondwanan hahnodontid teeth, removing them from multituberculates, and suggest that hahnodontid mammaliaforms had a much wider, possibly Pangaean distribution during the Jurassic-Cretaceous transition.
多瘤齿兽目是哺乳动物形类成功的一个分支，跨越了晚三叠世，至少到晚侏罗世，但它们的化石在欧亚大陆以外很少见，白垩纪的记录也存在争议。在这里，我们报告了所知的首个来自北美的基础白垩纪大型多瘤齿兽目的头骨。这个头骨具有混合的祖先哺乳动物形态的原始特征和冠哺乳动物的衍生特征。此外，它还显示出牙齿特征，这些特征与摩洛哥白垩纪被认为与多瘤齿兽类有关的孤立牙齿具有诊断意义，这些牙齿被归入神秘的“哈恩齿科”。这个标本的特殊保存状态也为了解祖先进化哺乳动物大脑提供了线索。我们证明了冈瓦纳哈恩齿科牙齿与多瘤齿兽目有关，将其从多瘤齿兽目中分离出来，并表明哈恩齿科哺乳动物在侏罗纪-白垩纪过渡时期的分布范围更广，可能是泛大陆范围。
