Conodont biostratigraphy of Upper Silurian formations from the Rabat- Tiflet area (northwestern Meseta, Morocco)

Les coupes siluriennes de la région de Rabat-Tiflet (Nord-Ouest de la Meseta marocaine) ont été systématiquement échantillonnées pour l’étude des conodontes. Parmi les espèces identifiées, il y a deux espèces-guides de la zonation silurienne européenne (Ozarkodina sagitta sagitta et Ozarkodina remscheidensis eosteinhornensis) et deux espèces guides de la zonation nord-américaine (Kockelella stauros et Kockelella variabilis). Ainsi la partie inférieure des formations de calcaires et de pélites du Silurien de la région de Rabat-Tiflet peut être attribuée aux zones à sagitta/ stauros et à variabilis inférieure. La présence de ces zones permet de reconnaître pour la première fois dans cette région la présence du Wenlock au dessous du Ludlow-Pridoli

A new icriodontid conodont cluster with specific mesowear supports an alternative apparatus motion model for Icriodontidae

Increasing numbers of conodont discoveries with soft tissue preservation, natural assemblages and fused clusters of the hard tissue have strengthened the hypothesis regarding the function and mechanism of the conodont feeding apparatus. Exceptional fossil preservation serves as a solid basis for modern reconstructions of the conodont apparatus illustrating the complex interplay of the single apparatus elements. Reliable published models concern the ozarkodinid apparatus of Pennsylvanian and Early Triassic conodonts. Recognition of microwear and mammal-like occlusion, especially of platform elements belonging to individuals of the genus Idiognathodus, allows rotational closure to be interpreted as the crushing mechanism of ozarkodinid platform (P1) elements. Here we describe a new icriodontid conodont cluster of Caudicriodus woschmidti that consists of one pair of icriodontan (I) and 10 pairs of coniform (C1\ue2\u80\u935) elements, with I elements being preserved in interlocking position. The special kind of element arrangement within the fused cluster provides new insights into icriodontid apparatus reconstruction and notation of elements. However, orientation of coniform elements is limited to a certain degree by possible preservational bias. Four possible apparatus models are introduced and discussed. Recognition of specific wear on denticle tips of one of the icriodontan elements forms the basis for an alternative hypothesis of apparatus motion. Analysis of tip wear suggests a horizontal, slightly elliptical motion of opposed, antagonistically operating I elements. This is supported by similar tip wear from much better preserved, but isolated, elements of Middle Devonian icriodontids. More detailed interpretation of the masticatory movement will allow enhanced understanding of anatomical specifications, diet and palaeobiology of different euconodont groups

Systematique, biogeographie et ecologie des Pleurotomariides post-paleozoieques

SIGLET 55578 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Upper Silurian to Middle Devonian conodont faunas from the Rabat-Tiflet area (northwestern Moroccan Meseta)

Conodont faunas are generally sparse in Pridolito middle Givetian deposits from the Rabat-Tiflet area in the north western Moroccan Meseta. The Pridoli and Lochkovian rocks consist of dark platy limestones alternating with dark shales containing graptolites in some levels. In the over lying part of the succession carbonate rocks predominate with the development of reefoid limestones in the lower Givetian. The eosteinhornensis, sulcatus, dehiscens vel kitabicus, laticostatus/inversus, partitus, ensensis, hemiansatus, timorensis and rhenanus/varcus zones have been recognized by occurrence of the conodont in dexspecies.The first appearance of Belodella devonica, occurring together with the graptolite Monograptus uniformis is used as a regional index species for the base of the Devonian. The age of some levels in the succession were previously dated by graptolites, dacryoconarids and rare goniatites