Maisey John G, Turner Susan, Naylor Gavin J P, Miller Randall F
Department of Vertebrate Paleontology, American Museum of Natural History, Central Park West, New York, New York, 10024-5192.
J Morphol. 2014 May;275(5):586-96. doi: 10.1002/jmor.20242. Epub 2013 Dec 18.
Doliodus problematicus is the oldest known fossil shark-like fish with an almost intact dentition (Emsian, Lower Devonian, c. 397Ma). We provide a detailed description of the teeth and dentition in D. problematicus, based on tomographic analysis of NBMG 10127 (New Brunswick Museum, Canada). Comparisons with modern shark dentitions suggest that Doliodus was a ram-feeding predator with a dentition adapted to seizing and disabling prey. Doliodus provides several clues about the early evolution of the "shark-like" dentition in chondrichthyans and also raises new questions about the evolution of oral teeth in jawed vertebrates. As in modern sharks, teeth in Doliodus were replaced in a linguo-labial sequence within tooth families at fixed positions along the jaws (12-14 tooth families per jaw quadrant in NBMG 10127). Doliodus teeth were replaced much more slowly than in modern sharks. Nevertheless, its tooth formation was apparently as highly organized as in modern elasmobranchs, in which future tooth positions are indicated by synchronized expression of shh at fixed loci within the dental epithelium. Comparable dental arrays are absent in osteichthyans, placoderms, and many "acanthodians"; a "shark-like" dentition, therefore, may be a synapomorphy of chondrichthyans and gnathostomes such as Ptomacanthus. The upper anterior teeth in Doliodus were not attached to the palatoquadrates, but were instead supported by the ethmoid region of the prechordal basicranium, as in some other Paleozoic taxa (e.g., Triodus, Ptomacanthus). This suggests that the chondrichthyan dental lamina was originally associated with prechordal basicranial cartilage as well as jaw cartilage, and that the modern elasmobranch condition (in which the oral dentition is confined to the jaws) is phylogenetically advanced. Thus, oral tooth development in modern elasmobranchs does not provide a complete developmental model for chondrichthyans or gnathostomes.
多利奥杜斯（Doliodus problematicus）是已知最古老的具有近乎完整齿列的鲨形鱼类化石（埃姆斯期，下泥盆纪，约3.97亿年前）。我们基于对NBMG 10127（加拿大新不伦瑞克博物馆）的断层扫描分析，对多利奥杜斯的牙齿和齿列进行了详细描述。与现代鲨鱼齿列的比较表明，多利奥杜斯是一种冲撞式捕食者，其齿列适合抓住并制服猎物。多利奥杜斯为软骨鱼类中“鲨形”齿列的早期演化提供了若干线索，同时也对有颌脊椎动物口腔牙齿的演化提出了新问题。与现代鲨鱼一样，多利奥杜斯的牙齿在齿系内沿着颌骨的固定位置以舌侧 - 唇侧顺序替换（在NBMG 10127中，每个颌骨象限有12 - 14个齿系）。多利奥杜斯牙齿的替换速度比现代鲨鱼慢得多。然而，其牙齿形成过程显然与现代板鳃类一样高度有序，在现代板鳃类中，未来牙齿的位置由牙上皮内固定位点处的shh同步表达指示。硬骨鱼类、盾皮鱼类和许多“棘鱼纲”动物中不存在类似的牙齿排列；因此，“鲨形”齿列可能是软骨鱼类和诸如托马坎图斯（Ptomacanthus）等有颌类动物的一个共源性状。多利奥杜斯的上前牙不附着于腭方骨，而是由脊索前基颅的筛骨区域支撑，这与其他一些古生代类群（如特里奥杜斯（Triodus）、托马坎图斯）情况相同。这表明软骨鱼类的牙板最初与脊索前基颅软骨以及颌软骨相关联，而现代板鳃类的情况（口腔齿列局限于颌骨）在系统发育上更为进化。因此，现代板鳃类的口腔牙齿发育并不能为软骨鱼类或有颌类动物提供一个完整的发育模型。
