The Microsyopidae are extinct mammals from the late Paleocene–late Eocene of North America and the late Paleocene of Europe. While results from phylogenetic analyses support euarchontan affinities, specific relationships of microsyopids to other plesiadapiforms (plausible stem primates), Euprimates (crown primates), Scandentia (treeshrews), and Dermoptera (colugos) are unresolved. An exceptionally well-preserved cranium of Microsyops annectens includes a basicranium that is generally primitive relative to that of other extinct and extant euarchontans in having: (1) a transpromontorial groove for an unreduced internal carotid artery (ICA) entering the middle ear posteromedially; (2) grooves (not tubes) on the promontorium, marking the course for both stapedial and promontorial branches of the ICA; (3) a foramen faciale that opens into the middle ear cavity, with the facial nerve exiting through a stylomastoid foramen primitivum; and (4) unexpanded caudal and rostral tympanic processes of the petrosal. The absence of any preserved bullar elements in the middle ear contrasts with that of other plesiadapiforms for which the region has been recovered, all of which have evidence of an ossified bulla. Microsyops lacks many of the specialized cranial characteristics of crown scandentians and dermopterans. The basicranial anatomy of microsyopids does not provide evidence in support of a clear link to any of the extant euarchontans, and suggests that the primitive morphology of this region in Euarchonta was little differentiated from that observed in the primitive placental mammals.

中文翻译：

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怀俄明州西北部始新世中期的 Microsyops annectens (Microsyopidae, Euarchonta, Mammalia) 的颅骨解剖

Microsyopidae 是北美古新世晚期至始新世晚期和欧洲古新世晚期已灭绝的哺乳动物。虽然系统发育分析的结果支持euarchontan 亲缘关系，但microsyopids 与其他plesiadapiforms（似是而非的茎灵长类动物）、Euprimates（皇冠灵长类动物）、Scandentia（树鼩）和皮肤翅目（colugos）的具体关系尚未得到解决。一个保存完好的颅骨显微观察包括一个相对于其他已灭绝和现存的euarchontans来说通常是原始的basicranium，它具有：（1）一个用于未缩小的颈内动脉（ICA）的经前沟，从后内侧进入中耳；(2) 前缘上的凹槽（不是管状），标记 ICA 镫骨和前缘分支的路线；(3) 面孔通入中耳腔，面神经通过茎乳孔原始孔离开；(4) 岩质的尾侧和头侧鼓室未扩张。中耳中没有任何保存的大泡元素与该区域已恢复的其他 plesiadapiforms 形成鲜明对比，所有这些都具有骨化大泡的证据。显微观察缺乏冠齿翅目和皮翅目动物的许多专门的颅骨特征。microsyopids 的颅底解剖并没有提供证据支持与任何现存的euarchontans 的明确联系，并表明Euarchonta 中该区域的原始形态与在原始胎盘哺乳动物中观察到的几乎没有区别。