Question

Passage A

The phenomenon known as the Cambrian explosion—a seemingly abrupt appearance of diverse macroscopic animal phyla in the fossil record approximately 540 million years ago—has long puzzled evolutionary biologists. Traditional paleontological interpretations take this fossil evidence at face value, concluding that animal life underwent a sudden, unprecedented period of rapid morphological diversification. However, this literal reading of the rock record fails to adequately account for profound taphonomic biases. The Cambrian period marks the widespread advent of biomineralization across multiple independent lineages—that is, the ability of organisms to precipitate hard skeletons, shells, or carapaces. Because hard parts are exponentially more likely to fossilize than soft tissues, the so-called "explosion" is fundamentally an illusion created by the sudden geological visibility of organisms that had actually been evolving and anatomically diversifying for tens of millions of years prior. Modern molecular clock analyses strongly corroborate this deep-time view. By measuring the genetic divergence between living animal groups and extrapolating backward based on estimated baseline mutation rates, geneticists have demonstrated that the deepest branches of the metazoan family tree originated well into the Precambrian, long before the earliest undisputed fossil evidence. The Cambrian fossil record, therefore, documents a profound change in the biochemical composition of animal anatomy, but it does not represent the initial evolutionary radiation of the animal lineages themselves.

Passage B

Recent molecular studies suggesting a deep Precambrian origin for basal animal lineages have prompted some evolutionary researchers to dismiss the Cambrian explosion as a mere taphonomic artifact of fossil preservation—specifically, the sudden acquisition of fossilizable hard parts by already diverse, but previously soft-bodied, lineages. This perspective, however, fundamentally conflates genetic divergence with morphological disparity and ecological innovation. While the abstract genetic lineages that would eventually become the major modern animal phyla may indeed have diverged genetically deep in the Precambrian, there is absolutely no evidence that these early common ancestors possessed the complex body plans, macroscopic size, and specialized ecological roles characteristic of their Cambrian descendants. The true evolutionary significance of the Cambrian explosion lies not in the cryptic, invisible branching of genetic lineages, but in the spectacular and remarkably sudden realization of macroscopic anatomical diversity and complex ecosystem engineering. Driven by newly forged macroscopic ecological interactions—such as the advent of active, vision-guided predation and the consequent evolutionary arms races—organisms rapidly evolved radically novel morphologies. These innovations included, but were certainly not limited to, biomineralized armor. To reduce the Cambrian explosion to a mere "biomineralization event" is to profoundly misunderstand the nature of evolutionary innovation. The explosion was a genuine, rapid, and historically unique proliferation of morphological disparity and ecological complexity, regardless of precisely when the genetic precursors of these animals first split from a common ancestor.

Based on the passages, both authors would be most likely to agree with which one of the following statements regarding the Precambrian ancestors of modern animal phyla?