Abstract
The Early Ordovician successions of the southern Montagne Noire consist of a thick sequence of predominantly siliciclastic sediments of which the late Tremadocian St. Chinian Formation and the earliest Floian La Maurerie Formation contain a comparatively rich and abundant cephalopod association. The cephalopods of the St. Chinian and La Maurerie Formation are interpreted as generally authochthonous, representing a fauna which originally lived in the open water above the sediments or related to the sea bottom. The cephalopod associations of the St. Chinian and La Maurerie formations are similar to other contemporaneous assemblages known from higher palaeolatitudes and associated with deeper depositional settings. They are composed almost exclusively of longiconic orthocones, in this case predominantly of eothinoceratids and baltocerids. The occurrences of <i>Annbactrocera</i>, and <i>Bactroceras</i> in the St. Chinian Formation are at present the earliest unambiguous reports of the Orthocerida. The available data suggest an initial expansion of orthoceroid cephalopod faunas from open water habitats of high paleo-latitudes, and a subsequent expansion on the carbonate platforms during the Floian. The presence of the eothinoceratid <i>Saloceras</i> in abundance demonstrates the Gondwanan affinity of the assemblage whilst adding further support for the presence of a "<i>Saloceras realm</i>" that may have extended along the margins of East and West Gondwana at least into intermediate latitudes. The following new taxa are proposed: <i>Annbactroceras</i> n. gen., <i>Annbactroceras felinense</i> n. sp., <i>Cyclostomiceras thorali</i> n. sp., <i>Felinoceras</i> n. gen., <i>Felinoceras constrictum</i> n. sp., <i>Lobendoceras undulatum</i> n. sp., Rioceratidae n. fam., <i>Saloceras murvielense</i> n. sp., <i>Thoraloceras</i> n. gen., <i>Thoraloceras bactroceroides</i> n. sp. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.201000013" target="_blank">10.1002/mmng.201000013</a>
Highlights
The available data suggest an initial expansion of orthoceroid cephalopod faunas from open water habitats of high paleo-latitudes, and a subsequent expansion on the carbonate platforms during the Floian
The presence of the eothinoceratid Saloceras in abundance demonstrates the Gondwanan affinity of the assemblage whilst adding further support for the presence of a ‘Saloceras realm’ that may have extended along the margins of East and West Gondwana at least into intermediate latitudes
By comparison with the relatively diverse Early Ordovician cephalopod faunas that lived in association with the low latitude carbonate platforms (e.g. Laurentia [Flower 1964]; Siberia [Balashov 1961]; China [Chen 1976]), those of the high latitude margins of Gondwana are of relatively low diversity, generally poorly known, and where known, often in need of revision
Summary
By comparison with the relatively diverse Early Ordovician cephalopod faunas that lived in association with the low latitude carbonate platforms (e.g. Laurentia [Flower 1964]; Siberia [Balashov 1961]; China [Chen 1976]), those of the high latitude margins of Gondwana are of relatively low diversity, generally poorly known, and where known, often in need of revision. Of those high latitudinal assemblages most recently revised or newly described in detail (Evans 2005; Gnoli & Pillola 2002; Marek et al 2000), all seem to be characterized by the presence (often in abundance) of members of the family Eothinoceratidae. Such an interpretation, based upon a single geographical datum, remains tentative
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