Mammalian development does not recapitulate suspected key transformations in the evolutionary detachment of the mammalian middle ear
Mammalian development does not recapitulate suspected key transformations in the evolutionary detachment of the mammalian middle ear
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DOI：
10.1098/rspb.2015.2606
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发表时间：
2016-01-13
影响因子：
4.7
通讯作者：
Weisbecker, Vera
中科院分区：
文献类型：
--
作者：
Ramirez-Chaves, Hector E.;Wroe, Stephen W.;Weisbecker, Vera
发育中的哺乳动物中耳(ME)的外鼓室、锤骨和砧骨最初通过Meckel‘s软骨附着在牙齿上，这表明它们起源于陆地脊椎动物的初级颌关节。这一概述引发了大多数未量化的建议，即导致哺乳动物ME的几个可疑的-但类似的未量化-关键进化转变在发育过程中被概括，通过ME骨骼相对于颌关节的负异速生长和后方/内侧移位。在这里，我们使用MU CT重建表明，在六种有袋动物和两种单孔动物的ME分离前发育过程中，异速生长和拓扑变化都是不可量化的。此外，在这两个单孔虫物种中不同的ME定位也没有被概括。这挑战了被广泛引用的最终哺乳动物中耳(DMME)进化情景的发展先决条件，突显了需要进一步的化石证据来测试这些假说。在有袋类动物中，后磨牙萌出、完全ME骨化和ME脱离之间可能存在关联，这表明齿状和ME之间的功能差异可能是ME发育和进化中ME分离的触发因素。牙齿和ME的稳定位置支持这样的说法，即在许多哺乳动物形式中发现的“部分哺乳动物中耳”--可能带有软骨的梅克尔氏软骨--是唯一在发育上看似合理的进化DMME前体。
The ectotympanic, malleus and incus of the developing mammalian middle ear (ME) are initially attached to the dentary via Meckel's cartilage, betraying their origins from the primary jaw joint of land vertebrates. This recapitulation has prompted mostly unquantified suggestions that several suspected-but similarly unquantified-key evolutionary transformations leading to the mammalian ME are recapitulated in development, through negative allometry and posterior/medial displacement of ME bones relative to the jaw joint. Here we show, using mu CT reconstructions, that neither allometric nor topological change is quantifiable in the pre-detachment ME development of six marsupials and two monotremes. Also, differential ME positioning in the two monotreme species is not recapitulated. This challenges the developmental prerequisites of widely cited evolutionary scenarios of definitive mammalian middle ear (DMME) evolution, highlighting the requirement for further fossil evidence to test these hypotheses. Possible association between rear molar eruption, full ME ossification and ME detachment in marsupials suggests functional divergence between dentary and ME as a trigger for developmental, and possibly also evolutionary, ME detachment. The stable positioning of the dentary and ME supports suggestions that a 'partial mammalian middle ear' as found in many mammaliaforms-probably with a cartilaginous Meckel's cartilage-represents the only developmentally plausible evolutionary DMME precursor.