> occurred 550 million years ago, during the Ediacaran period. [..]

> Although unclear whether this represents a true “mass extinction,” the percentage of organisms lost is similar to these other events, including the current, ongoing one.

> The researchers believe environmental changes are to blame for the loss of approximately 80% of all Ediacaran creatures, which were the first complex, multicellular life forms on the planet.

Pretty bad, but a very old extinction, and order of magnitude older than the dinosaurs' extinction.