A Walk Through Time

Animals Arise

600 Million Years Ago

The first animals arise when marine protoctists curtail reproduction in favor of specialization. They are very small, with only soft body parts, so they may swim with their protoctist cousins for millions of years before circumstances are favorable for their preservation in the fossil record.

Relatives of some of the first soft-bodied animals found in the fossil record.

Top left: This beautiful creature. just two thousandths of an inch long, is one of the smallest animals in the world. It is called a "rotifer" because the cilia of its tiny retracted wheel-like head beat and flush food toward its mouth. (Photograph by Richard Stemberger)

Top right: Tubeworms. (Photograph by Norman Meinkoth)

Mid left: Combo jelly (ctenophore). (Photograph courtesy Marine Biological Laboratory, Woods Hole)

Mid right: Blue buttons (cnidaria). (Photograph by Charles E. Cutress, Jr. Bertha M. Cutress)

Bottom: Colonial coral, Alcyonian, "dead men's fingers." (Photograph courtesy Marine Biological Laboratory, Woods Hole)

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