ABSTRACT A factor analysis of an exhaustive sample-based dataset of Cambrian (Miaolingian) to Silurian radiolarian species occurrences allows the detection of three evolutionary faunas composed of specific radiolarian families, which record simultaneous increases and decreases in radiolarian species richness over geological time. The oldest evolutionary fauna is composed of Cambrian to Early Ordovician archaeospicularians, assigned to the families Echidninidae and Palaeospiculidae, and of the entactinarian family Protoentactiniidae. This evolutionary fauna is complemented in the Early Ordovician by the oldest spumellarian family Antygoporidae, as well as by the order incertae sedis families Aspiculidae and Proventocitidae. Next, a new evolutionary fauna emerged during the Darriwilian and persisted during the Sandbian; it is dominated by the spumellarian family Inaniguttidae and to a lesser extent by the entactinarian families Haplentactiniidae, Entactiniidae and Pylentonemidae. Last, a third evolutionary fauna emerged since the Katian (Late Ordovician) and continued during the entire Silurian; it is dominated by the archaeospicularian family Secuicollactidae, the entactinarian family Paleoscenidiidae and the spumellarian family Haplotaeniatidae. These three early Palaeozoic radiolarian evolutionary faunas seem to correlate with major climatic and biotic changes known in the Ordovician: (i) the transition between the first and second evolutionary faunas is sharp and underlined by profound changes in taxonomic composition and turnover during the Middle Ordovician; it is correlated with the sudden early Darriwilian climate shift, global cooling and the main phase of the Great Ordovician Biodiversification Event (GOBE); (ii) the transition between the second and third evolutionary faunas is correlated with the Late Ordovician mass extinction (LOME; Katian–Hirnantian) and associated climate cooling.
Danelian et al. (Wed,) studied this question.