Oldest fossil animals found

From the Cryogenian period before the Cambrian.

Oldest Fossil Evidence for Animals Found | LiveScience

The ancient demosponges — probably measuring across no more than the width of a fork tine — were pinned down via fossilized steroids, called steranes, which are characteristic of the cell membranes of the sponges, rather than via direct fossils of the sponges themselves.

"The fact that we can detect sponge steranes at all suggests that by the Cryogenian Period [about 850 to 635 million years ago] demosponges were ecologically prominent and there were abundant demosponges living on the shallow sea floor," said geochemist Gordon D. Love of the University of California, Riverside, who headed up the analysis detailed in the Feb. 5 issue of the journal Nature.