Tuesday, January 27, 2009

Shaking up the Tree of Life

Earth may have given rise to two distinct groups of animals:
bilaterians -- animals with bilateral symmetry, like humans -- and
non-bilaterians, which include corals, jelly fish, hydra, unusual,
often poisonous, creatures known as cubozoans, and other organisms.

Ancestor For All Animals Identified : Discovery News
Although non-bilaterians and bilaterians appear to have followed separate evolutionary paths, nervous systems appear in both groups. Placozoans and sponges don't possess them, but many of their closely related taxa do.

"So this means that if our work is right, nervous systems evolved twice: Once in the lineage leading to bilateria and once in the lineage leading to corals, jelly fish, hydra and cubozoa," he said.

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