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Some Cretaceous long-looped terebratulide brachiopods analysed in the light of the diversity observed in the ontogeny of Recent representatives

¹ Université de Paris-Sud, Département des Sciences de la Terre, Bât. 509, F- 91405 Orsay cedex.

Abstract

The shape of the loop is of prime importance in brachiopod terebratulide classification and has been widely discussed and revised [Williams et al., 1996]. In the Rhynchonelliforma, we have focused our attention on the Terebratellidina, long-looped brachiopods with a wide-range diversity. The observation of its internal structure in recent representatives, investigated from the early growth stages, using the Scanning Electron Microscope (S.E.M.), demonstrates the complexity of its growth. Two main growth types of the descending branches are expressed during early ontogeny [Gaspard, 2002], followed in both cases by forward growth in opposite directions, with a brachial ribbon attached or unattached to the median septum. The purpose of such observations is to find in the fossil records similar growth types. An approach from the recent representatives allows a better knowledge of the Cretaceous taxa considered, even if the only way to recognise the loop is by means of transverse serial sections. The study of the recent terebratellidine loop facilitates the establishment of links between species from different geological periods. It helps to determine superfamilial distinctions and to find possible ancestors of recent terebratellidines.

Key Words: Terebratulide Brachiopods • Brachial ribbon • Diversity • Ontogeny • Cretaceous • Recent