Soru

The sudden disappearance of the enigmatic Ediacaran biota at the boundary of the Cambrian period has long prompted debate regarding whether their absence in the fossil record reflects a mass extinction or merely a closure of a taphonomic (preservational) window. Ediacaran fossils are predominantly impressions of soft-bodied organisms preserved in coarse-grained siliciclastic rocks—a highly unusual mode of preservation, given that coarse sediments typically allow oxygenated water to permeate, accelerating decay. The prevailing explanation for this preservational anomaly is the "death mask" hypothesis, which posits that extensive, leathery microbial mats blanketed the late Proterozoic seafloor. These mats are thought to have sealed the carcasses, creating localized anoxic microenvironments that facilitated the rapid precipitation of pyrite and silica, thereby casting the organisms' outlines before their tissues degraded.

With the onset of the Cambrian substrate revolution, the evolution of burrowing bilaterians—whose bioturbation disrupted the sediment—effectively destroyed the globally distributed microbial mats. Proponents of the taphonomic bias theory argue that the loss of these mats eliminated the unique preservational mechanism required to fossilize Ediacaran soft tissues in sandstone, rendering the organisms invisible to the fossil record rather than extinct. However, this theory struggles to account for paleontological findings in certain localized Cambrian environments. In hypersaline or severely dysoxic Cambrian basins where bioturbation was ecologically precluded, extensive microbial mats persisted. Yet, despite the presence of the necessary taphonomic conditions, these specific Cambrian strata yield only the remains of entirely different soft-bodied taxa, devoid of the distinctive quilted morphotypes characteristic of the Ediacaran biota. Consequently, while the destruction of microbial mats altered preservational regimes, the absence of Ediacaran organisms even where their requisite taphonomic window remained open strongly suggests that a genuine biological turnover occurred.

Based on the passage, which of the following inferences can be most reasonably drawn regarding the environmental dynamics of the late Proterozoic and early Cambrian periods?