fossil record

"Like many modern-day animal groups, ecdysozoans were prevalent in the Cambrian fossil record and we can see evidence of all three subgroups right at the beginning of this period, about 540 million years ago," said Ian Hughes, a graduate student in marine biology at Harvard University and the paper's first author.

But a UC Riverside-led team has now identified the oldest known ecdysozoan in the fossil record and the only one from the Precambrian period.

The earliest caviomorphs, which arrived during the Mid-Eocene Climatic Optimum, a period of elevated temperatures, were tiny, but Martinelli remarks there’s evidence of other extinct giant rodents in the fossil record.

Whether or not whales are actually speaking with one another, the fossil record shows that their ancestors evolved the ability to make sounds underwater tens of millions of years ago — long before human beings existed, let alone human language.

Its sparse fossil record left few clues to its disappearance.