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Evolutionary Development and Homoplasy of the Middle Ear in Early Mammal Evolution

机译：早期哺乳动物进化中耳的进化发育和同源性

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摘要

To understand the origins of complex structures and evolutionary novelties is a central quest in evolutionary studies.A key innovation in the early evolution of mammals is in the middle ear,a significant adaptation to sensitive hearing.The Definitive Mammalian Middle Ear (DMME),a major apomorphy of modem mammals,is defined by the loss of the embryonic Meckel's cartilage that connects the middle ear to the mandible in early ontogeny.The resorption of this cartilage in the adult separates the middle ear from the mandible,and this separation enhances the auditory function of the ear and the feedingfunction of the jaws.On the broadest scale of 310 million years of evolution of mammals from premammalian synapsid ancestors,transformation of the middle ear and its precursory structures appears to be incremental and orderly.However,recent discoveries of new fossils have demonstrated major evolutionary convergences and reversals,also known as homoplasy,in the middle ear structure among Mesozoic mammal clades.Some homoplasies of the middle ear structures in the Mesozoic mammals can now be correlated with heterochrony,or timing changes in ontogeny.Other homoplasies show the same phenotypic characteristics of gene patterning in the embryogenesis of extant mammals.Recent discoveries in new fossils and in developmental genetics have added to a growing body of evidence that the seemingly labile evolution of the middle ears in Mesozoic mammals was influenced,in a major way,by developmental heterochrony,and gene patteming.Changes in developmental genes and ontogenetic timing are a driving mechanism for the evolution of complex structures with major biological functions,as seen in the early evolution of mammalian ears.
机译：了解复杂结构和进化新奇的起源是进化研究的中心任务。哺乳动物早期进化的一项关键创新是在中耳，对敏感听觉的重要适应。权威的哺乳动物中耳（DMME），a现代哺乳动物的主要畸形是由在早期个体发育中将中耳连接到下颌骨的胚胎梅克尔软骨的丧失所定义的。成年后这种软骨的吸收将中耳与下颌骨分开，这种分离增强了听觉在前哺乳动物突触祖先的3.1亿年哺乳动物进化的最广泛规模上，中耳及其前体结构的转化似乎是有序的和渐进的。化石在中生代中耳结构中显示出主要的演化收敛和逆转，也称为同质性中生代哺乳动物的中耳结构的某些异质性现在可以与异时性或个体发育的时间变化相关联。发育遗传学方面的证据越来越多地表明，中生代哺乳动物中耳看似不稳定的发育在很大程度上受到发育异质性和基因模式的影响。发育基因的变化和个体发育的时机是驱动机制。如哺乳动物耳朵的早期进化所见，具有重要生物学功能的复杂结构的进化。

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