一件來自中國白堊紀(jì)地層已經(jīng)絕滅的小哺乳動物化石標(biāo)本的發(fā)現(xiàn)，填補(bǔ)了哺乳動物中耳形成之謎中的一個重要環(huán)節(jié)。爬行類的下頜骨由若干不同的骨片構(gòu)成，而在哺乳動物中下頜僅由一塊骨片構(gòu)成（即附著牙齒的齒骨）——大部分其余的骨片已經(jīng)演化為中耳的骨片（外鼓骨,、錘骨）。然而，卻一直沒有直接的化石證據(jù)記錄這一轉(zhuǎn)變,。

最近（4月14日）出版的《自然》雜志中，中國科學(xué)院古脊椎動物與古人類研究所客座研究員孟津等描述了一件化石標(biāo)本,，代表了三尖齒獸類的一個新種——胡氏遼尖齒獸(Liaoconodon hui),。其下頜成分已經(jīng)開始轉(zhuǎn)變?yōu)楝F(xiàn)生哺乳動物中耳的聽小骨。該種的外鼓骨和錘骨已經(jīng)不再和齒骨接觸,，但仍然通過一細(xì)長的骨化麥?zhǔn)宪浌桥c下頜相連,。研究者們認(rèn)為在哺乳動物的演化過程中，麥?zhǔn)宪浌菓?yīng)該起著保持穩(wěn)定的作用,，連接齒骨和已經(jīng)分離的聽小骨,。（生物谷Bioon.com）

生物谷推薦原文出處：

Nature   doi:10.1038/nature09921

Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont

Jin Meng,1, 2 Yuanqing Wang2 & Chuankui Li2

The transference of post-dentary jaw elements to the cranium of mammals as auditory ossicles is one of the central topics in evolutionary biology of vertebrates. Homologies of these bones among jawed vertebrates have long been demonstrated by developmental studies; but fossils illuminating this critical transference are sparse and often ambiguous. Here we report the first unambiguous ectotympanic (angular), malleus (articular and prearticular) and incus (quadrate) of an Early Cretaceous eutriconodont mammal from the Jehol Biota, Liaoning, China. The ectotympanic and malleus have lost their direct contact with the dentary bone but still connect the ossified Meckel’s cartilage (OMC); we hypothesize that the OMC serves as a stabilizing mechanism bridging the dentary and the detached ossicles during mammalian evolution. This transitional mammalian middle ear narrows the morphological gap between the mandibular middle ear in basal mammaliaforms and the definitive mammalian middle ear (DMME) of extant mammals; it reveals complex changes contributing to the detachment of ear ossicles during mammalian evolution.

胡氏遼尖齒獸(Liaoconodon hui)正型標(biāo)本（IVPP V16051）（王元青供圖）,。