Early development of rostrum saw-teeth in a fossil ray tests classical theories of the evolution of vertebrate dentitions.
Early development of rostrum saw-teeth in a fossil ray tests classical theories of the evolution of vertebrate dentitions.
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DOI：
10.1098/rspb.2015.1628
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发表时间：
2015-10-07
期刊：
影响因子：
--
通讯作者：
Johanson Z
中科院分区：
文献类型：
--
作者：
Smith MM;Riley A;Fraser GJ;Underwood C;Welten M;Kriwet J;Pfaff C;Johanson Z
在经典理论中，脊椎动物齿系的牙齿是由外部皮肤附着物共同进入口腔的。这一假说预测，有序的牙齿排列和定期更换在口腔牙列也来自皮肤dennelling。化石Batoid射线Schizorhiza stromeri（软骨鱼类;白垩纪）提供了一个测试这一理论。Schizorhiza保留了一个延伸的软骨喙，具有紧密间隔，交替的锯齿，与今天的锯鳐和锯鲨不同。多颗替换牙齿揭示了来自微CT扫描的独特新数据，显示了“锥中锥”系列有序锯齿集如何在发育过程中排列，并被预先存在的锯齿根部包围。在喙尖处，出现了新发育的锯齿，作为血管软骨沟内的矿化冠尖;这些通过两个90°旋转重新定向，然后在先前形成的根之间横向重新定位。锯齿替换减慢了中喙，在那里再生较少的锯齿。这些特殊的发展数据揭示了序列自我更新的调节顺序，保持锯齿边缘不断增加的锯齿大小。这模仿了软骨鱼类的牙齿替换，但不同之处在于牙冠的重新定向和它们直接在前任锯齿的根部之间的封闭。裂殖根的锯齿状发育与颌骨牙齿及其替换无关，依赖于牙板。这种高度特化的吻锯，源于皮肤牙本质的多样化，与牙列不同，并显示了皮肤牙本质潜在的发育可塑性。
In classical theory, teeth of vertebrate dentitions evolved from co-option of external skin denticles into the oral cavity. This hypothesis predicts that ordered tooth arrangement and regulated replacement in the oral dentition were also derived from skin denticles. The fossil batoid ray Schizorhiza stromeri (Chondrichthyes; Cretaceous) provides a test of this theory. Schizorhiza preserves an extended cartilaginous rostrum with closely spaced, alternating saw-teeth, different from sawfish and sawsharks today. Multiple replacement teeth reveal unique new data from micro-CT scanning, showing how the ‘cone-in-cone’ series of ordered saw-teeth sets arrange themselves developmentally, to become enclosed by the roots of pre-existing saw-teeth. At the rostrum tip, newly developing saw-teeth are present, as mineralized crown tips within a vascular, cartilaginous furrow; these reorient via two 90° rotations then relocate laterally between previously formed roots. Saw-tooth replacement slows mid-rostrum where fewer saw-teeth are regenerated. These exceptional developmental data reveal regulated order for serial self-renewal, maintaining the saw edge with ever-increasing saw-tooth size. This mimics tooth replacement in chondrichthyans, but differs in the crown reorientation and their enclosure directly between roots of predecessor saw-teeth. Schizorhiza saw-tooth development is decoupled from the jaw teeth and their replacement, dependent on a dental lamina. This highly specialized rostral saw, derived from diversification of skin denticles, is distinct from the dentition and demonstrates the potential developmental plasticity of skin denticles.