The bilateral log

Following sex - and predation; Kimberella (a mollusc) evolved bilateralism 558 Mya, also we hear of tubeworm Calyptrina. That is when different organs handle food intake and postfood exhaust. Petrov is on it, relating Julien Kimmig and Russell Bicknell.

(Some actual crap is involved in Kimmig-Bicknell being behind a paywall.)

The first Vendian/Ediacaran bilaterals did not drop deuces as the fossilisation process has (yet) preserved. These deuces get to the record in the Cambrian 538.8 Mya: microscopic at first, then growing to make the log. As it were.

Turns out that smaller animals produce smaller doodoo, such that these nutrients simply got BACTERIA'D. As noted I cannot read K-B but Petrov would imply that the first bilaterals weren't so different from the anemonai on this much. A mat of slime was laid down, by all. This didn't sequester all that much carbon, so the seas were still CO₂-rich and poor in oxygen.

Over the Cambrian, a feedback loop kicked in whereby larger animals dropped deuces that sequestered more carbon at a time. Oxygen increased, allowing for larger animals with their longer guts. The elder mats were meanwhile churned up by bottom feeders like the trilobites.

So far this just looks like more evidence for the Cambrian Explosion as explosion. We can still use that old just-so story Blink of an Eye to explain how certain animals suddenly were able to feast, and for their descendents to grow. To predationmaxx, said the book.