Tuesday, 7 February 2012

Proof that animals evolved much earlier than previously thought

The first animals: ca. 760-million-year-old sponge-like fossils from Namibia

Size: approx. 0.5 mm
One of the most profound events in Earth system evolution was the emergence of animals. The oldest, undisputed body fossils assigned an animal origin come from rocks between ca. 550 and 600 million years (Myr) old, yet molecular clock estimations place the origin of animals (thought to be sponges) considerably deeper in time (some 100-200 Myr earlier). Research by Bob Brain, Tony Prave, of the Department of Earth Sciences, and colleagues have recently discovered small fossils (the size of sand grains) in rocks in Namibia that resolve this discrepancy. The fossils are at least 760 Ma in age, thus within the timeframe of molecular clock predictions for the advent of animals. They have also offered a a provocative interpretation, namely, that those fossils are of small, sponge-like organisms that likely represent the ancestral stem group of all extent animal life. This discovery places the evolution of animals some hundreds of millions of years older than existing fossil data, and also show that these organism evolved prior to, and lived through, the severe climatic extremes of this geological time period known as Snowball Earth. [abstract][more]