This worm from 555 million years ago is probably your ancestor

Ikaria wariootia is the oldest known creature to be symmetrical down the midline with a front and a back.


NSFW    RIVERSIDE, CALIFORNIA — Geologists examining fossil impressions from South Australia have found evidence of the earliest relative of most animal life on Earth, a tiny, wormlike creature that lived 555 million years ago, according to a study published in the Proceedings of the National Academy of Sciences.

Writing in a news release, scientists at the University of California, Riverside say laser scans suggest the Ikaria wariootia was about the size of a grain of rice, 7mm long and 2.5mm wide at the largest. They were wide in the head, narrow in the rear, and possessed bilateral symmetry. This suggests they had a mouth, anus and gut.

The wormlike creatures are the oldest animals ever found to possess bilateral symmetry. This suggests they may be the first common ancestors to animals organized along the bilateral body plan, including dinosaurs, insects and humans.

According to the news release, bilateral symmetrical was a crucial evolutionary step that gave animals an efficient way to organize their body and to move purposefully.

The ocean floor-dwelling creatures lived during the Ediacaran Period. Scientists say the worms likely possessed senses that allowed them to navigate the well-oxygenated sands and search for organic matter to consume.
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