Ediacaran

As in our world, the Ediacaran is defined by the Vendozoans quickly diversifying, becoming the first widespread macroscopic organisms on Earth. But the main divergence will occur around 540 million years ago. In our timeline, burrowing worms started to proliferate around this time, leading to the Cambrian Substrate Revolution and the rapid collapse of the Ediacara Biota. However, it wouldn't be the case here.

The emergence of burrowing worms would be delayed by 15 million years, allowing the Vendozoans to take off and diversify. With the appearance of free-swimming forms, parasites, or ambush predators, all being less reliant on the microbial mat than their ancestors, the rapid changes in soil composition wouldn't be as much of an existential threat for the fauna.