The tommotiid<i><scp>K</scp>elanella</i>and associated fauna from the early<scp>C</scp>ambrian of southern<scp>M</scp>ontagne<scp>N</scp>oire (<scp>F</scp>rance): implications for camenellan phylogeny

Abstract

Abstract A carbonate bed of the P ardailhan F ormation, early C ambrian, southern M ontagne N oire (southern F rance), provided microfossils such as H yolithellus sp., T orellella cf. mutila and T orellella sp. along with numerous disarticulated pieces of composite skeletons such as valves of the brachiopod E oobolus priscus and of the bradoriid M onceretia erisylvia, and chancelloriid sclerites ( C hancelloria sp.). The assemblage also furnished a rich set of sclerites from the tommotiid K elanella altaica . Five morphological variations of the latter have been identified. The presence of concentric ribs formed by distal inflation of selected shell laminae in K elanella supports its assignment to the camenellans. More particularly, the presence of transverse structures within the internal cavity (septa) of K elanella suggests a close relationship with the L apworthellidae. However, the latter differ from K elanella by the continuous morphological variation along their scleritome which is also composed of simple conical elements with uniform ornamentation. Several forms of K elanella are similar to mitral and sellate sclerites of C amenella , whereas some other forms are comparable to K ennardia . The new material suggests that K elanella occupies a transitional position between L apworthellidae and the grouping of T ommotiidae and K ennardiidae. Such a phylogenetic position also implies that the number of sclerite morphotypes tends to decrease within the camenellan scleritome during evolution.