Shimada Kenshu
Environmental Science Program and Department of Biological Sciences, DePaul University, Chicago, Illinois 60614, USA.
J Morphol. 2002 Jan;251(1):38-72. doi: 10.1002/jmor.1073.
The dentitions of lamniform sharks are said to exhibit a unique heterodonty called the "lamnoid tooth pattern." The presence of an inflated hollow "dental bulla" on each jaw cartilage allows the recognition of homologous teeth across most modern macrophagous lamniforms based on topographic correspondence through the "similarity test." In most macrophagous lamniforms, three tooth rows are supported by the upper dental bulla: two rows of large anterior teeth followed by a row of small intermediate teeth. The lower tooth row occluding between the two rows of upper anterior teeth is the first lower anterior tooth row. Like the first and second lower anterior tooth rows, the third lower tooth row is supported by the dental bulla and may be called the first lower intermediate tooth row. The lower intermediate tooth row occludes between the first and second upper lateral tooth rows situated distal to the upper dental bulla, and the rest of the upper and lower tooth rows, all called lateral tooth rows, occlude alternately. Tooth symmetry cannot be used to identify their dental homology. The presence of dental bullae can be regarded as a synapomorphy of Lamniformes and this character is more definable than the "lamnoid tooth pattern." The formation of the tooth pattern appears to be related to the evolution of dental bullae. This study constitutes the first demonstration of supraspecific tooth-to-tooth dental homologies in nonmammalian vertebrates.
鼠鲨目的鲨鱼牙齿据说呈现出一种独特的异形齿，称为“鼠鲨状齿型”。每个颌骨软骨上存在一个膨胀的中空“牙泡”，这使得通过“相似性测试”基于地形对应关系，能够识别大多数现代大型噬食性鼠鲨目的同源牙齿。在大多数大型噬食性鼠鲨目中，上牙泡支撑着三排牙齿：两排大的前牙，后面跟着一排小的中间牙。位于两排上前牙之间咬合的下牙排是第一排下前牙。与第一和第二排下前牙一样，第三排下牙也由牙泡支撑，可称为第一排下中间牙。下中间牙排在位于上牙泡远端的第一和第二排上侧牙排之间咬合，其余的上、下牙排，都称为侧牙排，交替咬合。牙齿对称性不能用于确定它们的牙齿同源性。牙泡的存在可被视为鼠鲨目的一个共源性状，而且这个特征比“鼠鲨状齿型”更具可定义性。齿型的形成似乎与牙泡的进化有关。这项研究首次证明了非哺乳动物脊椎动物中种上水平的牙齿与牙齿之间的同源性。
