New Early Cambrian bivalved arthropods from southern France

Abstract

International audienceThe Lower Cambrian Pardailhan Formation of the Montagne Noire (Southern France) has yielded a diverse fossil assemblage including bivalved arthropods (the bradoriids Monceretia erisylvia gen. et sp. nov., Cambria danvizcainia sp. nov. and Matthoria? sp., together with Isoxys sp.) associated with trilobites, hyolithids, inarticulate brachiopods, sponge spicules, ichnofossils and chancelloriid sclerites. This assemblage provides new evidence about the biodiversity of Early Cambrian marine communities in palaeocontinentalGondwana. The bradoriids are Cambriidae, a familywith widespread distribution in offshore shelf marine environments during Early Cambrian times. The present study confirms the presence of cambriids within a subtropical latitudinal belt that encompasses Laurentia, Siberia and the Gondwanan margins from Southern France to South China. Although knowledge of the distribution of fossil cambriids is patchy, at the generic level they appear to be provincial, with Petrianna from Laurentia, Shangsiella and Auriculatella from South China, Cambria from Siberia and Gondwana (Armorica), and Monceretia gen nov. from Gondwana (Armorica). The presence of Isoxys in the Montagne-Noire confirms the cosmopolitan distribution of this genus in the Early and Middle Cambrian tropics. Cambriid bradoriids occupy a biostratigraphically narrow time interval, probably equating to part of the Atdabanian and Botomian stages of Russian terminology. Their presence in the Pardailhan Formation supports the notion of a Botomian age, determined from archaeocyathan evidence. The North American bradoriid genus Matthoria, also possibly present in the Pardailhan Formation, is reassigned to the Cambriidae

New bradorid arthropods from the Lower Cambrian of Spain

“…The new findings from Montagne Noire (Vannier et al 2005) and Córdoba are Ovetian in age, and supplement this biochronological record (text- fig. 4).…”

“…Cambriids have fairly large carapaces, which are characterized by a distinct anterior-dorsal downslope and a typical surface sculpture that consists of nodes and ridges. Their discovery in Spain adds to their known records from different parts of the world such as North America, Greenland , France (Vannier et al 2005), Siberia, and Southwest China (e.g., Hou et al 2002).…”

“…According to Siveter et al (1996), Hou et al (2002 and Vannier et al (2005) the family Cambriidae comprises the following genera: Cambria Neckaya and Ivanova 1956, Shangsiella Lee 1975, Auriculatella Tan 1980, Petrianna Siveter et al 1996, and Monceretia Vannier and Williams in Vannier et al 2005. Their regional and biostratigraphic occurrences are given in text-figure 4.…”

“…Recently, Hou et al (2002) Siveter et al 1996). Vannier et al 2005 introduced Cambria danvizcainia and Monceretia erisylvia from the Montagne Noire (France), both species coming from the basal Pardailhan Formation; this formation contains archaeocyaths and trilobites of upper Ovetian age.…”

Two species ofHesslandona(Phosphatocopida, Crustacea) from the Upper Cambrian of western Hunan, South China and the phylogeny of Phosphatocopida

“…The doublure is a structure positioned between the inner lamella and the outer surface of the shield and extends anteriorly and posteriorly continuously towards the dorsal rim. The doublure is a common character among various arthropods of different evolutionary grades especially among those shields with wide lateral extensions, e.g., stem-lineage arthropod Shankouia zhenghei Chen et al, 2005in Waloszek et al, 2005, Sunellids (Zhang and Shu, 2007, Squamacula clypeata Bergströ m, 1997 (Zhang et al, 2004), Isoxys (Stein et al, 2010), bradoriids (Vannier et al, 2005;Zhang, 2007;Topper et al, 2011), Agnostus pisiformis (Wahlenberg, 1818) (Mü ller andWalossek, 1987) and other trilobites, and the stem-lineage crustacean Henningsmoenicaris scutula (Haug et al, 2010a). It also occurs among ostracod eucrustaceans but is more difficult to depict among other eucrustaceans (Maas et al, 2003).…”