Smith M M
Proc R Soc Lond B Biol Sci. 1979 Mar 26;204(1154):15-39. doi: 10.1098/rspb.1979.0010.
The histology of tooth plates of Sagenodus inaequalis has been investigated to obtain information on the histogenesis of the tissue. The histological mechanisms of growth and replacement of the tooth plate are described in terms of an increase in area of the tooth plate by addition of denticles to the lateral margins of the ridges, replacement of worn dentine at the tritoral surface by basal growth of dentine and invasive growth of dentine into the surrounding bone at the anterior and medial margins. The histogenesis of a specialized character for dipnoans is described, namely hypermineralized dentine, or petrodentine, within the tooth plates. This has placed an advanced character further back in the phylogenetic organization of dipnoans than was previously recognized. The implications of these observations are discussed in relation to proposed phylogenies and previous observations on tooth plates of other dipnoans. It is concluded that Sagenodus inaequalis shared a common ancestor with both the ceratondontids and the lepidosirenids. A sequence is proposed for the phyletic relationship of tooth plate-bearing dipnoans. From a consideration of the features of histogenesis of this specialized dentine, the alternative terminologies are reviewed and petrodentine (Lison 1941) chosen for the hypermineralized dentine and syndentine (Thomasset 1928) as the collective term for the entire mass of dentine in the tooth plate.
对不等萨根鱼（Sagenodus inaequalis）齿板的组织学进行了研究，以获取有关该组织组织发生的信息。齿板生长和替换的组织学机制表现为：通过在嵴的侧缘添加小齿来增加齿板面积；在研磨面磨损的牙本质通过牙本质的基底生长进行替换；在齿板前部和内侧边缘，牙本质侵入周围骨骼。文中描述了肉鳍鱼类的一个特殊特征的组织发生，即在齿板内存在高度矿化的牙本质，即石化牙本质。这表明这一高级特征在肉鳍鱼类的系统发育组织中的位置比之前认为的更靠后。结合已提出的系统发育关系以及之前对其他肉鳍鱼类齿板的观察结果，对这些观察结果的意义进行了讨论。得出的结论是，不等萨根鱼与角齿鱼科和美洲肺鱼科拥有共同的祖先。文中提出了一个带有齿板的肉鳍鱼类系统发育关系的序列。通过对这种特殊牙本质组织发生特征的考虑，对不同的术语进行了回顾，并选择石化牙本质（利松，1941年）来指代高度矿化的牙本质，选择联合牙本质（托马塞特，1928年）作为齿板中整个牙本质团块的统称。
