Variations du rythme du développement chez les trilobites Phacopidae néodévoniens

Catherine CRÔNIER & Philippe COURVILLE

fr Comptes Rendus Palevol 2 (6-7) - Pages 577-585

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

Developmental variations in neodevonian phacopide trilobites

Heterochrony refers to changes in the timing and the rate of development of ancestral morphological features. This phenomenon has been observed in some neodevonian phacopide trilobites. Their evolution is marked by progressive displacement of the visual complex towards the external margins, accompanied by displacement of the facial suture. This evolutionary pathway is a result of paedomorphosis. These features seem to be adaptative, and may occur in all lineages, leading to convergences between several taxa. A paedomorphic phenomenon also concerns the change of moulting behaviour. This particular feature may not be related to environment but represents a feature inherited from the ancestral forms.


Trilobites, Phacopida, Devonian, heterochrony, morphological variability

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