6533b7d4fe1ef96bd1263084

RESEARCH PRODUCT

Trajectoires ontogénétiques et hétérochronies complexeschez des ammonites (Harpoceratinae) du Jurassique inférieur (Domérien)

subject

description

Evolutive transformations of ontogeny in the two main groups of Harpoceratinae which colonize the North-West Europe during the lower Domerian — Protogrammoceras (Matteiceras) and Protogrammoceras (Fieldingiceras) — are analyzed. Within P. (Matteiceras) these transformations belong to a strict heterochronical logic (translation of a standard ontogenetic trajectory). Within P. (Fieldingiceras) the alterations of the ontogeny cannot be placed in a same logic. Moreover, the P. (Matteiceras) heterochronical issues are complex: paedomorphic (neoteny) and peramorphic (acceleration) tendencies appear on both sides of critical point (inversion point) for a same feature, the ribs density.