Análise dos parâmetros macroevolutivos do clado Archaeocyatha (Porifera) e demonstração de dois intervalos biologicamente distintos na extinção do início do Cambriano

Abstract

The Cambrian Period is usually associated with the greatest adaptive radiation of metazoans ever documented. Less remembered, however, is the fact that the period includes, right at its beginning, the first extinction of the Phanerozoic Eon — a paleobiological process of major importance for understanding metazoan evolution. The Early Cambrian Extinction Event is linked to the abrupt disappearance of a large portion of newly diversified faunal lineages. Among the different groups affected by this event, the greatest loss of diversity occurred in the clade Archaeocyatha, a group with a long history of taxonomic interpretations, now attributed to the Phylum Porifera. The Archaeocyatha constitute the first group of metazoans to form reef structures and are among the oldest mineralized skeleton-producing animals. Understanding their diversification and extinction dynamics is a fundamental step in elucidating the causes and mechanisms of the Early Cambrian Extinction Event. This research aims to reconstruct the macroevolutionary dynamics of the Archaeocyatha clade through Bayesian statistical modeling, estimating speciation, extinction, and net diversification rates over geological time, based on a broad and revised fossil record. For this purpose, this study analyzed species-level taxonomic diversification rates of the Archaeocyatha clade using fossil data compiled from the Paleobiology Database (PBDB) and specialized literature. The analysis included 448 fossil occurrences, divided among 175 species. Analyses were performed in the PyRate software, employing an RJ-MCMC algorithm and variable preservation rates, while accounting for classical biases such as the Signor-Lipps effect. An auxiliary methodology was also used to ensure sampling efficacy through the Tracer 1.7.1 software. The results point to an extinction event divisible into two biologically distinct intervals, associated with changes in the clade’s net diversification rate. The first interval is linked to an abrupt drop in speciation rates, temporally related to the establishment of the Chengjiang fauna, while the second interval is associated with a sudden increase in extinction rates, compatible with the Sinsk Event and the Early Toyonian Regression Event, but preceding their current dating by approximately 5 million years.