Morphometries of the Late Devonian conodont genus Palmatolepis:: phylogenetic, geographical and ecological contributions of a generic approach

Studying the palaeobiology of extinct organisms relies on assessing the relevant scale of morphometric differentiation corresponding to the evolutionary units in the group. On the time-slice of the latest Frasnian, sampled in nine outcrops from three distant palaeogeographical domains (Laurussia, northwest and northeast Gondwana), the morphological pattern of differentiation of the conodont genus of Pahnatolepis was analysed based on the outline of its platform elements. A generic approach was used that challenged the concept of species in this genus but supported the distinction between two subgenera. In the samples considered here, Pahnatolepis Pahnatolepis includes the single species linguiformis, and Pahnatolepis Manticolepis appears as a homogeneous group composed of a single species or a complex of closely related species. The former displays mostly an isometric growth whereas the allometric growth of the latter means that the difference between the two subgenera increases with the size of the elements. Shape difference of an element belonging to the feeding apparatus may be related to differences in ecology. Hence, the differences in size and shape between the two subgenera may be interpreted as related to differences in their ecological preferences and life history traits.