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Journal of Paleontology

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DIVERSITY OR DISPARITY IN THE JURASSIC (UPPER CALLOVIAN) GENUS KOSMOCERAS (AMMONITINA): A MORPHOMETRIC APPROACH

¹ Université Rennes I, UMR 6118 du CNRS, 363 Av. Général Leclerc, 35042 Rennes Cedex, <Philippe.Courville{at}univ-rennes1.fr>
² Université des Sciences et Technologies de Lille 1, UMR 8014 et FR 1818 du CNRS, Laboratoire de Paléontologie et Paléogéographie du Paléozoïque, 59655 Villeneuve d'Ascq Cedex, France, <Catherine.cronier{at}univ-lille1.fr>

A detailed morphometric approach applied to the diversity (interspecific variation)/disparity (intraspecific range of variation) was developed. It was based on outline analysis, and it was applied to 41 cross sections of Kosmoceras from the Upper Callovian of eastern France (Prusly). The cross sections represent an excellent basis for evaluation of the global shape of the shell: the main morphologic descriptors include the proportion of umbilical diameter/conch diameter and the thickness of the whorl; they also indirectly describe the ornament that influences the aspect of the whorl section. This analysis was conducted to quantify the size and shape variations and to determine the relations among some of the ‘morphological species’ defined by Tintant: K. bizeti, K. fibuliferum, K. phaienum? and K. interpositum? Numerous analyzed individuals may not belong to these categories.

The results suggest that despite a wide range of variability four main morphotypes can be ascribed a probable taxonomic status, whose mean representatives can be properly assigned to Tintant's four ‘species.’ Moreover, three of them could constitute a morphological series, continuously related through ontogeny. The fourth (K. interpositum) may be an independent species, rarely recovered in the studied area.