Titre
Ontogeny and covariation in the Toarcian genus Osperleioceras (Ammonoidea)
Type
article
Institution
UNIL/CHUV/Unisanté + institutions partenaires
Périodique
Auteur(s)
Morard, A.
Auteure/Auteur
Guex, J.
Auteure/Auteur
Liens vers les personnes
Liens vers les unités
ISSN
0037-9409
Statut éditorial
Publié
Date de publication
2003
Volume
174
Première page
607
Dernière page/numéro d’article
615
Peer-reviewed
Oui
Langue
anglais
Résumé
Starting from embryonic (protoconch-ammonitella) and early juvenile shells, which are indistinguishable at the species level, growth curves of Osperleioceras from the Reynesi Subzone (Upper Toarcian) of the Causses Basin (Aveyron, France) show a continuous radiating range of correlated variation in dimensional and ornamental characters, such as involution, whorl compression, rib strength and rib density. This covariation pattern can be observed among single-horizon assemblages, as well as during individual ontogenetic development.
The existence of a continuous intergradational series of shells, ranging from stout coarsely ribbed to smooth suboxycone morphologies, rules out functional or ecological selectivity to explain this non-random variability pattern. The complex interdependence of shape and sculpture can be simulated by a model in which sculpture intensity depends on mantle curvature [GUEX, 1999].
The expression of covariation in subadult specimens since the base of Upper Toarcian reveals a rise in variability, concomitant with a size decrease, both contemporaneous with environmental instability. It developed in successive bursts from a fairly long low variability period spanning the whole Middle Toarcian.
The existence of a continuous intergradational series of shells, ranging from stout coarsely ribbed to smooth suboxycone morphologies, rules out functional or ecological selectivity to explain this non-random variability pattern. The complex interdependence of shape and sculpture can be simulated by a model in which sculpture intensity depends on mantle curvature [GUEX, 1999].
The expression of covariation in subadult specimens since the base of Upper Toarcian reveals a rise in variability, concomitant with a size decrease, both contemporaneous with environmental instability. It developed in successive bursts from a fairly long low variability period spanning the whole Middle Toarcian.
PID Serval
serval:BIB_98E90F5B019A
Date de création
2007-11-19T09:41:38.866Z
Date de création dans IRIS
2025-05-20T22:06:05Z