ABSTRACT

The cochlear canal of Adalatherium hui, from the Late Cretaceous of Madagascar, exhibits a combination of features previously unknown among mammaliaforms. The cochlear canal of Adalatherium is short and ‘C’-shaped (curved through at least 210°). A presumptive lagenar nerve canal extends from the apex of the cochlea to the internal acoustic meatus. In conjunction with an apical expansion of the cochlear canal, this morphology suggests that Adalatherium retained a lagenar macula. Adalatherium is derived among mammaliaforms in possessing primary and secondary osseous laminae, a cribriform plate, and a distinct cochlear ganglion canal. Strikingly, Adalatherium shows a single-layered primary osseous lamina that lacks internal, radially oriented canaliculi for auditory nerve fibers. In this respect, the primary lamina of Adalatherium is structurally different from the double-layered primary lamina containing habenulae perforatae of extant therians. Furthermore, Adalatherium resembles the gondwanatherian Vintana in possessing a secondary canal running parallel to the cochlear ganglion canal. Although its exact role and homology are uncertain, the morphology of this secondary canal and its tributary canaliculi is most consistent with a vascular function. The inner ear of Adalatherium augments a growing list of characters (or character combinations) in which gondwanatherians are not only different from the inferred plesiomorphic condition for mammaliaforms but also distinct from the derived characters of therians. Collectively, the new morphological and phylogenetic data support homoplastic transformation of such structures as the cribriform plate and primary osseous lamina in mammals and independent loss of the lagenar macula within gondwanatherians.

摘要

来自马达加斯加晚白垩世的Adaatherium hui的耳蜗管展现了哺乳动物形式以前未知的特征的组合。Adalatherium的耳蜗管短且呈“ C”形（弯曲至少210°）。推定的舌状神经管从耳蜗的根尖延伸到内耳道。与耳蜗根尖的扩张相结合，这种形态表明Adalatherium保留了gen状黄斑。Adalatherium来源于具有初级和次级骨层，筛状板和独特的耳蜗神经节管的哺乳动物。惊人地，Adalatherium显示的是单层初生骨板，缺少用于听神经纤维的内部径向小管。在这方面，Adamatherium的初生叶片在结构上不同于现存的扇贝类的含有哈贝努尔穿孔的双层初生叶片。此外，Adalatherium类似于冈瓦纳特式的Vintana，拥有一条平行于耳蜗神经节管的辅助管。尽管其确切的作用和同源性尚不确定，但该次管及其支管的形态与血管功能最一致。内耳Adalatherium从而增加了越来越多的字符（或字符组合）列表，在这些字符中，冈瓦纳德人不仅与推断的哺乳动物形式的多形性条件不同，而且与锡安人的衍生字符不同。总的来说，新的形态学和系统发育数据支持哺乳动物中筛状板和原发性骨板等结构的同型转化，以及在冈瓦纳特人体内独立发生的层状黄斑的丢失。