Scientists have discovered evidence of the world's earliest animals, dating back 635 million years, before the end of the last ice age. Earliest, 635-million-year-old animal remains detected in sedimentary  rocks in Oman

Scientists have found evidence of the world's earliest multicellular animal life, sponges 408 million years older than the oldest known dinosaur remains, 100 million years older than when scientists thought the first animal life appeared.

Earth scientist Gordon Love of the University of California, Riverside led the team that made the discovery. He says the 635-million-year-old fossils were found in sedimentary rocks in a seabed in southern Oman and are in the form of steroids, essential biochemicals in the cell membranes of sponges.

"Some of the natural products produced by sponges produce very distinctive structures," said Love. "Even when they get buried for hundreds-of-millions of years in sediments. Basically when the structures of the molecules get tweaked a little bit, we can still recognize the basic fundamental skeleton that alerts us to the fact that these were produced by ancient sponges."

Love says it appears the ancient sponges lived on the sea floor and were only a few millimeters in size. He adds that research will now focus on whether environmental changes between the two great ice ages caused animal life to flourish.

"Did the glacial periods provide some sort of environmental stimulus which sort of reorganized the ecosystems forever? Did the animals appear as we fell into the glacial [period] or did they appear after the glaciation, is really the next question, I think? We want to really tie the first appearance of multicellular animals [sponges] with a better understanding of the context of the environment in which they first appeared," he said.

The study by Gordon Love and his colleagues is published in this week's edition of the journal Nature.