The Cambrian Explosion: macroevolution and biomineralization

Abstract

Recent advances in our understanding of the Cambrian evolutionary diversification event (Cambrian Explosion) show that although eumetazoan stem taxa were present in the late Proterozoic, a tremendous burst of macroevolutionary change occurred near the beginning of the Cambrian. Explanations relying on paleoecological feedback are insufficient to explain the macroevolutionary patterns observed, particularly those associated with the near-simultaneous appearance of new higher taxa. The diversity of biomineralization types among the small shelly fossils of the early Cambrian Period can be explained if putative ancestral scleritome bearers (found in both Proterozoic Eon and Cambrian Period strata) had, as some new data suggest, intact scleritomes that hosted individual sclerites of varying biomineral composition.

The origin of eukaryotes and rise in complexity were synchronous with the rise in oxygen

“…However, this calibration fell into doubt 3 years later with the discovery of a possible 890 million-year-old sponge (metazoan) fossil (Turner, 2021). One subsequent author considers it to be a trace fossil of a metazoan rather than a whole body fossil (McMenamin, 2023), but this would not undermine its value as a minimum calibration for Metazoa here. Other authors (McMenamin and Kris, 2021;Neuweiler et al, 2022) do not rule out that this fossil may be a keratose sponge, but propose verification for that and all other Frontiers in Bioinformatics frontiersin.org keratose sponge fossils.…”

The Internal Anatomy and Water Current System of Cambrian Archaeocyaths of South China

“…The canal-bearing fossils (Figure 6) may also represent the "missing link" between typical archaeocyaths and metazoans. The hollow canals provide evidence favoring a hypothesis about archaeocyath affinities that the archaeocyaths may represent an "archaeozoan" grade of organization that is intermediate between the metazoan and parazoan grade [85,86]. Nevertheless, more well-preserved material and more advanced techniques should be employed to further examine the affinity of these intriguing and important taxa.…”