Slug mark clue to early animal life

19:05, Jun 28 2012

Burrowing tracks made by a centimetre-long prehistoric slug have pushed the earliest traces of animal life back 30 million years. The soft-bodied creature left its marks in a region of silty sediment in central Uruguay called the Tacuari Formation. Rock dating has determined that the tracks are 585 million years old, 30 million years older than any previously known animal traces. Unlike simpler life forms, true animals such as the slug are "bilaterian" and have a front and back as well as an upper and lower side. The new findings suggest that bilaterian animals appeared between ice ages during the early Ediacaran period. Story continues ADVERTISEMENT This pre-dates the "Cambrian explosion" when life diversified into a myriad different forms. Scientists believe the slug-like creature grazed through sediments at the bottom of a shallow sea. The team, led by Dr Ernesto Pecoits from the University of Alberta in Canada, wrote in the journal Science: "It appears as though a maximum interval of 50 million years exists between the earliest definitive evidence of sponges and the bilaterians found in the Tacuari Formation, which implies that early animal evolution took place on a geologically rapid time scale once environmental conditions proved favourable for higher forms of life to colonise the ocean realm." Prior to the new discovery the oldest evidence of bilaterian animal life, found in Russia, dated back 555 million years.

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