Trilobite diversity patterns in the Middle Cambrian of southwestern Europe: a comparative study

This paper describes the pattern of trilobite diversity throughout the Middle Cambrian in two fossiliferous basins of the western Gondwana margin: the Iberian Chains (northeastern Spain) and the Montagne Noire (southern France). The documented fluctuations of species diversity allow us to recognize: (1) a substantial extinction event recorded in latest Early Cambrian times (named Valdemiedes event), which separates the culmination of a widespread decline of trilobites and the stepwise immigration of cosmopolitan invaders; (2) a major trilobite radiation occurring in the earliest Leonian and culminating across the Caesaraugustian/Languedocian transition, in which a peak in diversity of trilobites and carpoids was close to a major flooding surface; (3) a major reduction of trilobite taxa across the early/middle Languedocian transition related to a well-documented regressional trend; and (4) a second immigration of trilobite fauna in the late Languedocian which coincided with trangressional pulses and the establishment of suitable shaly substrates. In addition, we summarize the known trilobite occurrences from the Middle Cambrian of southwestern Europe. Maps of the distribution of some relevant taxa (genera and species) over the western Gondwana margin are documented.