Abstract

ZAMORA, Samuel et al. A new carpoid (class Cincta Jaekel, 1918) from northern Spain and its bearing on the functional morphology of the operculum. Ameghiniana [online]. 2007, vol.44, n.4, pp.727-738. ISSN 1851-8044.

Cinctan carpoids from Middle Cambrian (Languedocian) rocks of northern Spain are described. Sampled specimens probably belong to a new species of the genus Gyrocystis Jaekel; nevertheless, the lack of some key features prevents against erecting formally a new taxon at this moment. A functional interpretation of the operculum is made, and the evolutionary meaning of some structures related with its movement is analysed herein. When the opercular area of different cinctans (Asturicystis, Sotocinctus and Gyrocystis) are compared, it is concluded that several features in Gyrocystis sp. L were probably related to a better mobility of the operculum. These are the lesser number of postopercular plates anchored to the operculum, the reduction of the postopercular facet, a more rigid lintel, and the existence of quite big adopercular facets on the inner side of the adopercular processes. All these features permitted Gyrocystis sp. L a higher efficiency in expelling water out of the theca, and they can be interpreted as apomorphies in the evolutionary history of cinctans. The term postopercular facet is defined here as the articulation structure between the operculum and the postopercular plates.

Keywords : Cincta; Middle Cambrian; Spain; Functional morphology.