Integrated records of environmental change and evolution challenge the Cambrian Explosion

Abstract

The 'Cambrian Explosion' describes the rapid increase in animal diversity and abundance, as manifest in the fossil record, between ~ 540 and 520 million years ago (Ma). This event, however, is nested within a far more ancient record of macrofossils extending at least into the late Ediacaran, ~571 Ma. The evolutionary events documented during the Ediacaran-Cambrian interval coincide with geochemical evidence for the modernisation of Earth's biogeochemical cycles. Holistic integration of fossil and geochemical records leads us to challenge the notion that the Ediacaran and Cambrian worlds were markedly distinct, and places biotic and environmental change within a longer-term narrative. We propose that the evolution of metazoans may have been facilitated by a series of dynamic and global changes in redox conditions and nutrient supply, which, together with potential biotic feedbacks, enabled turnover events that sustained phases of radiation. In this synthesis, we argue that early metazoan diversification should be recast as a series of successive, transitional radiations that extended from the late Ediacaran and continued through the early Palaeozoic. We conclude that while the Cambrian Explosion represents a radiation of crown-group bilaterians, it was simply one phase amongst several older, and younger, metazoan radiations.

On the co‐evolution of surface oxygen levels and animals

“…657–645 Ma). Although our view of late Ediacaran and early Cambrian biotic diversity is still being refined, what will not change is clear evidence for major shifts in ecosystem structure and complexity through the Ediacaran and early Cambrian, coincident with a record of increasingly diverse animals (Darroch, Smith, Laflamme, & Erwin, ; Tarhan et al, ; Wood et al, ). And in that light, late Neoproterozoic and Cambrian biotic transitions are largely not about skeletonization, or all about animals.…”

The importance of neutral over niche processes in structuring Ediacaran early animal communities

“…1) and is comprised entirely of soft-bodied sessile organisms that are preserved in situ beneath volcanogenic/volcaniclastic event beds. These event beds have deep-water depositional settings (Wood et al 2003;Narbonne 2005) that are dated to~571-560 Ma (Noble et al 2015;Pu et al 2016), and are considered to represent early animals (Budd & Jensen 2017;Dunn et al 2018;Wood et al 2019). As such, bedding plane surfaces are interpreted to preserve near-complete census paleocommunities Wood et al 2003), although the impact of modern erosion needs to be considered (Matthews et al 2017;cf.…”

The Developmental Gene Hypothesis for Punctuated Equilibrium: Combined Roles of Developmental Regulatory Genes and Transposable Elements

“…In contrast to the invertebrates we see today, however, it has been proposed that during the Cambrian period there was a much wider array of body plans, that is, the so‐called “Cambrian explosion,” a concept which Gould made famous in his 1989 book, Wonderful Life: The Burgess Shale and the Nature of History . It is now believed that rather than a single explosion, the Ediacaran–Cambrian interval experienced a series of significant radiations more akin to successive fireworks . Nevertheless, the variety in bauplan present in the Burgess Shale Lagerstätte, along with features of “interchangeable parts” of some of these strange creatures as suggested by Gould, indicates that CNE may have been experiencing a significant evolutionary flux during these early periods in metazoan evolution prior to entrenchment.…”