目前，科学家将3.8亿年前一种远古鱼类化石放在最新高能量X射线仪下进行扫描分析，形成的3D图像能够真实呈现这种远古鱼类的模样，证实这种鱼类是第一种像现代哺乳动物发育形成下颌的动物。
最新3D成像显示3.8亿年前的盾皮鱼拥有下颌和牙齿，暗示着人类进化形成牙齿和下颌的时期要更早
研究人员称，我们人类的咧齿微笑或许应当感谢这种3.8亿年前漫游海洋的远古鱼类——盾皮鱼，它们的牙齿并不是最漂亮的，但对于脊椎动物进化史却至关重要。这表明人类发育形成牙齿和下颌的时代要早于之前的预期。
这个3.8亿年前的盾皮鱼化石，挖掘发现于澳大利亚，在最新高能量X射线仪下能够呈现出真实的3D结构图。来自英国、瑞士和澳大利亚的一支联合研究小组通过重建该鱼类嘴部结构，发现它还拥有下颌和牙齿。这意味着人类可能进化得更快，之前认为它们可能形成类似剪刀一样的下颌能够撕碎动物尸体，之后进化形成适当的牙齿。
之前科学家认为牙齿和下颌的形成仅出现于数百万年前的脊椎动物，其历史时期晚于盾皮鱼的出现，这是一种体形较小的鱼类，长着盔甲状皮肤。
来自英国布里斯托尔大学、伦敦自然历史博物馆、澳大利亚科廷大学的古生物学家以及瑞士物理学家，共同完成这项研究报告，现发表在《自然》杂志上。
他们使用最新的高能量成像仪在瑞士保罗-谢勒研究所绘制出盾皮鱼的真实模样，来自布里斯托尔大学的马丁-鲁克林说：“我们能够呈现盾皮鱼下颌骨骼中任何组织和细胞，有助于更进一步地研究它的下颌和牙齿。”
菲利浦-多诺霍教授补充称，这是证实首个拥有下颌骨骼的脊椎动物存在牙齿的确凿证据，并能解释牙齿的起源之谜。
来自伦敦自然历史博物馆的合著作者泽里娜-约翰逊说：“这是保存非常完好的一块澳大利亚鱼类化石，它将揭晓更多关于人类进化祖先的秘密。”（生物谷Bioon.com）
doi:10.1038/nature11555
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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.
