Oldest bilateral animals

The same fossil deposits that yielded the earliest bilateral embyros also contain fossils of a very small animal. They are about 1/5 of a millimetre long—barely visible. The fossils come from sediments that are 580 to 600 million years old. (That’s 90 million years before the Cambrian explosion.) They are about 25 million years older than the earliest known macroscopic bilateran. (The picture shows the animal’s mouth, with some pits on either side that may be primitive sense organs.)

Researchers named the animal Vernanimalcula, or “small spring animal,” because it appeared soon after the last total glaciation, or “Snowball Earth” period. In The New Scientist magazine, Jeff Hecht writes:

“As well as many microscopic sponges, they found 10 tiny oval fossils of animals with a multilayered body including a mouth, gut and anus – the hallmarks of bilateral animals.”

In other words, this is an organism with a front end. Guy Narbonne of Queen’s University in Kingston, Ontario, Canada, is impressed by the new organism:

“What I find most intriguing is how closely it matches the most recent predictions of molecular and developmental biology.”

See “Tiny fossils reveal key step in animal evolution”.

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