目前，科學(xué)家將3.8億年前一種遠(yuǎn)古魚類化石放在最新高能量X射線儀下進(jìn)行掃描分析,，形成的3D圖像能夠真實(shí)呈現(xiàn)這種遠(yuǎn)古魚類的模樣，證實(shí)這種魚類是第一種像現(xiàn)代哺乳動物發(fā)育形成下頜的動物,。
最新3D成像顯示3.8億年前的盾皮魚擁有下頜和牙齒,，暗示著人類進(jìn)化形成牙齒和下頜的時期要更早
研究人員稱，我們?nèi)祟惖倪铸X微笑或許應(yīng)當(dāng)感謝這種3.8億年前漫游海洋的遠(yuǎn)古魚類——盾皮魚,，它們的牙齒并不是最漂亮的,，但對于脊椎動物進(jìn)化史卻至關(guān)重要。這表明人類發(fā)育形成牙齒和下頜的時代要早于之前的預(yù)期,。
這個3.8億年前的盾皮魚化石,，挖掘發(fā)現(xiàn)于澳大利亞，在最新高能量X射線儀下能夠呈現(xiàn)出真實(shí)的3D結(jié)構(gòu)圖,。來自英國,、瑞士和澳大利亞的一支聯(lián)合研究小組通過重建該魚類嘴部結(jié)構(gòu)，發(fā)現(xiàn)它還擁有下頜和牙齒,。這意味著人類可能進(jìn)化得更快,，之前認(rèn)為它們可能形成類似剪刀一樣的下頜能夠撕碎動物尸體，之后進(jìn)化形成適當(dāng)?shù)难例X,。
之前科學(xué)家認(rèn)為牙齒和下頜的形成僅出現(xiàn)于數(shù)百萬年前的脊椎動物,，其歷史時期晚于盾皮魚的出現(xiàn)，這是一種體形較小的魚類,，長著盔甲狀皮膚,。
來自英國布里斯托爾大學(xué),、倫敦自然歷史博物館、澳大利亞科廷大學(xué)的古生物學(xué)家以及瑞士物理學(xué)家,，共同完成這項(xiàng)研究報告,，現(xiàn)發(fā)表在《自然》雜志上。
他們使用最新的高能量成像儀在瑞士保羅-謝勒研究所繪制出盾皮魚的真實(shí)模樣,，來自布里斯托爾大學(xué)的馬丁-魯克林說：“我們能夠呈現(xiàn)盾皮魚下頜骨骼中任何組織和細(xì)胞,，有助于更進(jìn)一步地研究它的下頜和牙齒。”
菲利浦-多諾霍教授補(bǔ)充稱,，這是證實(shí)首個擁有下頜骨骼的脊椎動物存在牙齒的確鑿證據(jù),，并能解釋牙齒的起源之謎。
來自倫敦自然歷史博物館的合著作者澤里娜-約翰遜說：“這是保存非常完好的一塊澳大利亞魚類化石,，它將揭曉更多關(guān)于人類進(jìn)化祖先的秘密,。”（生物谷Bioon.com）
doi:10.1038/nature11555
PMC:
PMID:
Development of teeth and jaws in the earliest jawed vertebrates
Martin Rücklin, Philip C. J. Donoghue, Zerina Johanson, Kate Trinajstic, Federica Marone & Marco Stampanoni
Teeth and jaws constitute a model of the evolutionary developmental biology concept of modularity and they have been considered the key innovations underpinning a classic example of adaptive radiation. However, their evolutionary origins are much debated. Placoderms comprise an extinct sister clade or grade to the clade containing chondrichthyans and osteichthyans, and although they clearly possess jaws, previous studies have suggested that they lack teeth that they possess convergently evolved tooth-like structures or that they possess true teeth. Here we use synchrotron radiation X-ray tomographic microscopy (SRXTM) of a developmental series of Compagopiscis croucheri (Arthrodira) to show that placoderm jaws are composed of distinct cartilages and gnathal ossifications in both jaws, and a dermal element in the lower jaw. The gnathal ossification is a composite of distinct teeth that developed in succession, polarized along three distinct vectors, comparable to tooth families. The teeth are composed of dentine and bone, and show a distinct pulp cavity that is infilled centripetally as development proceeds. This pattern is repeated in other placoderms, but differs from the structure and development of tooth-like structures in the postbranchial lamina and dermal skeleton of Compagopiscis and other placoderms. We interpret this evidence to indicate that Compagopiscis and other arthrodires possessed teeth, but that tooth and jaw development was not developmentally or structurally integrated in placoderms. Teeth did not evolve convergently among the extant and extinct classes of early jawed vertebrates but, rather, successional teeth evolved within the gnathostome stem-lineage soon after the origin of jaws. The chimaeric developmental origin of this model of modularity reflects the distinct evolutionary origins of teeth and of component elements of the jaws.
