A Jurassic mammal, far more advanced than we usually think such beings were, has been discovered in China. Though apparently unrelated to living lines, it had the tail of a beaver and, apparently, a lifestyle something like an otter or platypus.
We often think that because we have a few fossils we have some idea of what the ecological and evolutionary web was in “Deep Time”. We do not.
Aso here is an article on “ice worms”, fascinating little creatures that live on glaciers in the Pacific Northwest and die and turn to mush at even moderate temps. Go here for photos and more detailed info. “On Suiattle Glacier, … on the south side of Glacier Peak, the recorded mean density was ~2600 ice worms per square meter in 2002. With an area of 2.7 square kilometers, this represents somewhat over 7 BILLION ice worms on this glacier! This is more than the earth’s entire human population on just one glacier”.