Cambrian radiation speciation events driven by sea level and redoxcline changes on the Siberian Craton

Abstract

The evolutionary processes of speciation during the Cambrian radiation and their potential extrinsic drivers, such as episodic oceanic oxygenation events, remain unconfirmed. High-resolution temporal and spatial distribution of reef-associated archaeocyath sponge species on the Siberian Craton during the early Cambrian [ca. 528 to 510 million years ago] shows that speciation was driven by increased endemism particularly ca. 521 million years (59.7% endemic species) and 514.5 million years (65.25% endemic species) ago. These mark rapid speciation events after dispersal of ancestors from the Aldan-Lena center of origin to other regions. These speciation events coincided with major sea-level lowstands, which we hypothesize were intervals when relative deepening of the shallow redoxcline permitted extensive oxygenation of shallow waters over the entire craton. This provided oxic corridors for dispersal and allowed the formation of new founder communities. Thus, shallow marine oxygen expansion driven by sea-level oscillations provides an evolutionary driver for sucessive speciation events during the Cambrian radiation.

Sea level controls on Ediacaran-Cambrian animal radiations

“…This is inferred from the early Cambrian record of the Siberian Platform, which shows that phases of increased diversity of reef biota coincide with a deepening of the habitable zone on the shallow marine shelf which, in turn, is interpreted to correspond with a possible deepening of the redoxcline ( 56 ). These phases also coincide with increased speciation during local sea level lowstands, and it is suggested that lowstand intervals permitted extensive oxygenation of shallow waters over the entire craton, thereby providing oxic corridors for dispersal and the creation of new founder communities ( 55 ).…”

“…Increasing atmospheric oxygen concentration may have deepened the redoxcline, so extending habitable water depths, promoted animal-sediment mixing [e.g., ( 52 )], and allowed for the evolution of more metabolically costly ecologies such as carnivory, in turn driving a predator-prey “arms race” and hence diversification ( 53 ). Spatially and temporally dynamic shallow marine anoxia itself might have formed physical barriers to dispersal, thereby promoting reproductive isolation and speciation ( 54 , 55 ). This is inferred from the early Cambrian record of the Siberian Platform, which shows that phases of increased diversity of reef biota coincide with a deepening of the habitable zone on the shallow marine shelf which, in turn, is interpreted to correspond with a possible deepening of the redoxcline ( 56 ).…”