Boyer Doug M, Kirk E Christopher, Silcox Mary T, Gunnell Gregg F, Gilbert Christopher C, Yapuncich Gabriel S, Allen Kari L, Welch Emma, Bloch Jonathan I, Gonzales Lauren A, Kay Richard F, Seiffert Erik R
Department of Evolutionary Anthropology, Duke University, Durham, NC 27708, USA; Division of Fossil Primates, Duke Lemur Center, Durham, NC 27705, USA.
Department of Anthropology, University of Texas, Austin, Austin, TX, USA; Jackson School Museum of Earth History, University of Texas, Austin, Austin, TX, USA.
J Hum Evol. 2016 Aug;97:123-44. doi: 10.1016/j.jhevol.2016.06.002. Epub 2016 Jul 13.
Primate species typically differ from other mammals in having bony canals that enclose the branches of the internal carotid artery (ICA) as they pass through the middle ear. The presence and relative size of these canals varies among major primate clades. As a result, differences in the anatomy of the canals for the promontorial and stapedial branches of the ICA have been cited as evidence of either haplorhine or strepsirrhine affinities among otherwise enigmatic early fossil euprimates. Here we use micro X-ray computed tomography to compile the largest quantitative dataset on ICA canal sizes. The data suggest greater variation of the ICA canals within some groups than has been previously appreciated. For example, Lepilemur and Avahi differ from most other lemuriforms in having a larger promontorial canal than stapedial canal. Furthermore, various lemurids are intraspecifically variable in relative canal size, with the promontorial canal being larger than the stapedial canal in some individuals but not others. In species where the promontorial artery supplies the brain with blood, the size of the promontorial canal is significantly correlated with endocranial volume (ECV). Among species with alternate routes of encephalic blood supply, the promontorial canal is highly reduced relative to ECV, and correlated with both ECV and cranium size. Ancestral state reconstructions incorporating data from fossils suggest that the last common ancestor of living primates had promontorial and stapedial canals that were similar to each other in size and large relative to ECV. We conclude that the plesiomorphic condition for crown primates is to have a patent promontorial artery supplying the brain and a patent stapedial artery for various non-encephalic structures. This inferred ancestral condition is exhibited by treeshrews and most early fossil euprimates, while extant primates exhibit reduction in one canal or another. The only early fossils deviating from this plesiomorphic condition are Adapis parisiensis with a reduced promontorial canal, and Rooneyia and Mahgarita with reduced stapedial canals.
灵长类物种通常与其他哺乳动物不同，它们具有骨管，在颈内动脉（ICA）分支穿过中耳时将其包围。这些骨管的存在和相对大小在主要灵长类分支中各不相同。因此，ICA鼓岬支和镫骨支管道解剖结构的差异，被认为是早期神秘的化石真灵长类动物属于类人猿或原猴亚目亲缘关系的证据。在这里，我们使用显微X射线计算机断层扫描技术，汇编了关于ICA管道大小的最大定量数据集。数据表明，某些群体中ICA管道的变异比之前认为的更大。例如，鼬狐猴和毛耳狐猴与大多数其他狐猴科动物不同，它们的鼓岬管道比镫骨管道大。此外，各种鼬狐猴科动物在管道相对大小上存在种内变异，一些个体的鼓岬管道比镫骨管道大，而另一些个体则不然。在鼓岬动脉为大脑供血的物种中，鼓岬管道的大小与颅内容积（ECV）显著相关。在具有替代脑供血途径的物种中，鼓岬管道相对于ECV高度缩小，并且与ECV和颅骨大小都相关。结合化石数据的祖先状态重建表明，现存灵长类动物的最后一个共同祖先的鼓岬和镫骨管道大小相似，且相对于ECV较大。我们得出结论，冠层灵长类动物的近祖状态是有一条为大脑供血的开放鼓岬动脉和一条为各种非脑结构供血的开放镫骨动脉。这种推断的祖先状态在树鼩和大多数早期化石真灵长类动物中都有体现，而现存灵长类动物则在某一条管道上出现了缩小。唯一偏离这种近祖状态的早期化石是巴黎阿氏猴，其鼓岬管道缩小，以及鲁尼猴和玛格丽塔猴，其镫骨管道缩小。
