First, here is an “official” opinion that the Cambrian period half a billion years ago really was an explosion of life forms:
Although the cause of the influx of oxygen remains a matter a scientific controversy, Sperling called the Cambrian radiation that followed “the most significant evolutionary event in the history of animals.”
And this from someone who just wants an establishment job:
“During the Cambrian period essentially every major animal body plan — from arthropods to mollusks to chordates, the phylum to which humans belong — appeared in the fossil record,” said Sperling, who is scheduled to join Scripps as a postdoctoral researcher through National Science Foundation support.
Now, that settled, he argues that the rise of carnivores dunit. An increase in oxygen enabled a carnivorous lifestyle:
The authors linked this proliferation of life to the evolution of carnivorous feeding modes, which require higher oxygen concentrations. Once oxygen increased, animals started consuming other animals, stimulating the Cambrian radiation through an escalatory predator-prey “arms race.”
The assumption is that carnivory requires higher oxygen levels because carnivores require a higher energy level than prey.
Interesting how interpreting the history of life through Darwin’s lenses means a constant search for the one accidental change that made a huge difference. It usually turns out that there is a co-ordinated suite of changes that made a huge difference. Darwinism requires them to be in competition with each other simply because recognition of a co-ordinated suite would require recognition of design. So claims for a single simple mechanism are always at war with each other.