Les hétérochronies du développement : un outil pour l'étude de la variabilité et des relations phylétiques ? Exemple de Nigericeras, Ammonitina du Crétacé supérieur africain

Philippe COURVILLE & Catherine CRÔNIER

fr Comptes Rendus Palevol 2 (6-7) - Pages 535-546

Published on 30 November 2003

This article is a part of the thematic issue Les chemins de l’Évolution : sur les pas de Steven Jay Gould

Ontogenetic heterochronies: a tool to study both variability and phyletic relationships? Example: Nigericeras , Ammonitina of the african Upper Cretaceous

The Nigericeras gadeni ontogenesis (Saharian Upper Cretaceous) is characterized by three ornamental stages: multi-tuberculate inner-whorls, ombilical bi-tuberculate medium-whorls, then finally smooth adult stage. Ontogenetic Heterochonies account for their adult variability, which extends between both paedomorphic (thick/ornamented) morphotype, and peramorphic (thin/smooth) morphotype. That species may take root in the older Pseudocalycoceras. A peramorphocline characterizes the evolution of these ammonites and their younger relatives, leading to different Nigerian and Nigerien, highly compressed taxa. Such morphologies seem to be related to shallow-water palaeo-environments. The general transgressive context leads to the progressive scarcity of their supposed ecological niches.


heterochronies, peramorphosis, Ammonitina, Upper Cretaceous, Sahara

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