Data from: Unraveling species concepts for the Helicoprion tooth whorl

The genus Helicoprion (Chondricthyes: Euchondrocephali) is preserved
primarily by a continuous spiral root that forms the base for more than
130 teeth. Helicoprion is found globally in Lower Permian marine rocks and
at least 100 specimens exist in public collections worldwide. Ten species
of the genus are reviewed in the context of new morphometric analyses
conducted on dozens of specimens. Helicoprion whorls share a common inner
spiral geometry that results in exponential growth of tooth and root
dimensions. Novel growth equations permit calculation of whorl diameter,
volution number and tooth count from incomplete specimens. The results of
meristic and geometric analyses identify taxobases that distinguish three
emended species concepts. Differentiation of form is evident among
specimens only after the second volution or roughly the 85th tooth.
Helicoprion davisii has widely-spaced, stout teeth with tall cutting
surfaces and is distinguished from H. bessonowi, whi ch has narrow,
closely-spaced teeth with short cutting surfaces. H. ergassaminon is an
intermediate form, having narrow, closely-spaced teeth with tall cutting
surfaces. Several large specimens in the study are too dissimilar to place
in the new emended species concepts.

旋齿鲨属（Helicoprion，软骨鱼纲Chondrichthyes：真软骨颅类Euchondrocephali）的化石记录主要以一段连续的螺旋状齿根为代表，该齿根为超过130颗牙齿提供了附着基座。旋齿鲨的化石在全球各地的下二叠统海相岩层中均有产出，目前全球公共馆藏的标本至少有100件。本研究结合对数十件标本开展的全新形态测量分析，对该属的10个物种进行了系统厘定。旋齿鲨的齿旋具有统一的内部螺旋几何构型，使得牙齿与齿根的尺寸呈指数级增长。本研究提出的全新生长方程，可通过不完整的标本计算其齿旋直径、旋卷数与牙齿总数。通过计数学与几何形态学分析得到的结果，确立了可区分3个修订物种概念的分类学依据。仅当齿旋发育至第二旋卷（约对应第85颗牙齿）时，不同标本间的形态分化才会显现。戴维斯旋齿鲨（Helicoprion davisii）的牙齿间距宽阔、齿体粗壮，且具有较高的切割刃面；其与贝氏旋齿鲨（Helicoprion bessonowi）特征迥异，后者的牙齿窄小且排列紧密，切割刃面较短。埃尔加辛旋齿鲨（Helicoprion ergassaminon）为过渡类群，其牙齿窄小且排列紧密，但切割刃面较高。本研究中的几件大型标本与上述修订物种的特征差异显著，无法归入新的修订物种范畴。