據(jù)10月9日的《科學(xué)》雜志報(bào)道說，對(duì)像人類這樣的胎盤哺乳動(dòng)物或像袋鼠那樣的有袋類哺乳動(dòng)物的史前先祖的化石進(jìn)行分析后發(fā)現(xiàn),，哺乳動(dòng)物獨(dú)特的中耳在進(jìn)化的時(shí)候發(fā)生了消失及重新出現(xiàn)等多次的演化,。 這種定義性的哺乳動(dòng)物特性是以在胚胎期中耳與顎骨的分離以及Meckel軟骨的喪失為特征的,。
在哺乳動(dòng)物中所發(fā)現(xiàn)的多次進(jìn)化顯示，進(jìn)化方式并非僅僅是以原始的種系進(jìn)化為衍生的種系這種線性的方式出現(xiàn),，人們還可在時(shí)間的長(zhǎng)河中發(fā)現(xiàn)進(jìn)化的逆轉(zhuǎn),，即逆轉(zhuǎn)成更為原始的特征和情況。
Qiang Ji及其同僚為了得出這些結(jié)論,，他們對(duì)儲(chǔ)放在中國河南地質(zhì)博物館中的白堊紀(jì)早期的哺乳動(dòng)物Maotherium（或譯：毛獸）的化石進(jìn)行了分析,。 該動(dòng)物化石[屬于一個(gè)會(huì)演變?yōu)橛写惣疤ケP哺乳動(dòng)物的種系]的中耳仍然與其顎骨融合，即使在該動(dòng)物的先祖版本中,，其中耳與其顎骨已經(jīng)分離了,。由于發(fā)育學(xué)的研究已經(jīng)顯示，中耳與顎骨的分離與發(fā)育時(shí)的多個(gè)基因及信號(hào)途徑有關(guān),，因此這些研究人員提示,，在子宮中的基因表達(dá)模式及變化可能導(dǎo)致了哺乳動(dòng)物獨(dú)特性的中耳早期的多次進(jìn)化。
在一篇相關(guān)的Perspective中,，Thomas Martin和 Irina Ruf更為詳細(xì)地解釋了這些發(fā)現(xiàn),。（生物谷Bioon.com）
生物谷推薦原始出處：
Science 9 October 2009:DOI: 10.1126/science.1178501
Evolutionary Development of the Middle Ear in Mesozoic Therian Mammals
Qiang Ji,1 Zhe-Xi Luo,2,* Xingliao Zhang,3 Chong-Xi Yuan,1 Li Xu3
The definitive mammalian middle ear (DMME) is defined by the loss of embryonic Meckel’s cartilage and disconnection of the middle ear from the mandible in adults. It is a major feature distinguishing living mammals from nonmammalian vertebrates. We report a Cretaceous trechnotherian mammal with an ossified Meckel’s cartilage in the adult, showing that homoplastic evolution of the DMME occurred in derived therian mammals, besides the known cases of eutriconodonts. The mandible with ossified Meckel’s cartilage appears to be paedomorphic. Reabsorption of embryonic Meckel’s cartilage to disconnect the ear ossicles from the mandible is patterned by a network of genes and signaling pathways. This fossil suggests that developmental heterochrony and gene patterning are major mechanisms in homplastic evolution of the DMME.
1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China.
2 Carnegie Museum of Natural History, Pittsburgh, PA 15213, USA.
3 Henan Geological Museum, Zhengzhou 450003, China.
