LANDMARK-BASED MORPHOMETRIC ANALYSES OF IDIOGNATHODUS MAGNIFICUS AND DEVELOPMENT OF COMPREHENSIVE PROTOCOLS TO STUDY MORPHOLOGICAL VARIATION IN CONODONT P1 ELEMENTS

Two landmark-based morphometric procedures were used to analyze P₁ elements of Idiognathodus magnificus Stauffer and Plummer, 1931 from the Upper Pennsylvanian Beeman Formation of the Sacramento Mountains of New Mexico. The first procedure uses landmarks on P₁ elements of Idiognathodus and Streptognathodus species to analyze morphological variation in platform shape, as shown by Hogancamp et al. (2016) for the I. simulator group. The second procedure modifies the first by the addition of additional landmark points that are defined by lobe shape and position. The strength of the first procedure is that it allows comparison between most species of Idiognathodus and Streptognathodus, regardless whether lobes are present or not and can be used as a standard procedure to study shape variability within these groups. The second procedure describes morphological variation better in two-lobed P₁ elements, but can only be used on two-lobed elements. Results from both types of morphometric analyses show that I. magnificus has the same pattern of P₁ element asymmetry as seen in the I. simulator group, where the rostral margin is wider on the ventral end of the dextral element than it is on the sinistral element (Hogancamp et al., 2016). Specimens of I. magnificus are distinguished from specimens of the I. simulator group by having longer adcarinal ridges and more symmetrical platform margins. This illustrates the robust applicability of the first procedure to study morphological variability between different species of Idiognathodus. Both analyses demonstrate that two morphotypes of I. magnificus with asymmetrical P₁ element pairs can be diagnosed based on lobe variation and platform shape. One P₁ element morphotype pair has more elongate rostral lobes on both P₁ elements than the other.