Itano Wayne M, Lambert Lance L
1Museum of Natural History, University of Colorado, Boulder, CO 80309 USA.
2University of Texas at San Antonio, San Antonio, TX 78249 USA.
Zoological Lett. 2018 Jun 6;4:12. doi: 10.1186/s40851-018-0097-8. eCollection 2018.
Paleozoic holocephalian tooth plates are rarely found articulated in their original positions. When they are found isolated, it is difficult to associate the small, anterior tooth plates with the larger, more posterior ones. Tooth plates are presumed to have evolved from fusion of tooth files. However, there is little fossil evidence for this hypothesis.
We report a tooth plate having nearly perfect bilateral symmetry from the Mississippian (Chesterian Stage) Bangor Limestone of Franklin County, Alabama, USA. The high degree of symmetry suggests that it may have occupied a symphyseal or parasymphyseal position. The tooth plate resembles ? St. John and Worthen, 1883, but differs in having a sharp ridge with multiple cusps arranged along the occlusal surface of the presumed labiolingual axis, rather than a relatively smooth occlusal surface. The multicusped shape is suggestive of a fused tooth file. The middle to latest Chesterian (Serpukhovian) age is determined by conodonts found in the same bed.
The new tooth plate is interpreted as an anterior tooth plate of a chondrichthyan fish. It is referred to Itano and Lambert, gen. et sp. nov. ? is also referred to .
古生代全头亚纲的齿板很少在其原始位置以关节相连的形式被发现。当它们被单独发现时，很难将较小的前齿板与较大的、更靠后的齿板联系起来。齿板据推测是由齿列融合进化而来。然而，这一假说几乎没有化石证据。
我们报道了一块来自美国阿拉巴马州富兰克林县密西西比纪（切斯特阶）班戈石灰岩的齿板，它具有近乎完美的双侧对称性。高度的对称性表明它可能占据了联合或副联合位置。该齿板类似于？圣约翰和沃特森，1883年，但不同之处在于，沿着假定的唇舌轴的咬合面有一条带有多个尖牙的锐脊，而不是相对光滑的咬合面。多尖形状暗示着融合的齿列。通过在同一层位发现的牙形刺确定其时代为切斯特阶中期至晚期（谢尔普霍夫阶）。
新的齿板被解释为一种软骨鱼类的前齿板。它被归入伊塔诺和兰伯特，新属及新种？也被归入。
