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 mill..
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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.
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