First discovered gliding along glass in laboratory aquariums just over 100 years ago, placozoans are animals that lack a nervous system and possess four types of body cells. DeSalle explained that, "placozoa, because of their simple body plans and their position in our tree, are a good candidate for the common ancestor of non-bilaterian animals." 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. Neil Blackstone, professor of ecology and evolution at Northern Illinois University, told Discovery News, "There is no doubt that Rob and his colleagues are leaders in the study of evolutionary relationships among animals." Blackstone agreed that, "evolution need not be progressive. Perhaps there are two fundamentally different kinds of animals." He added, "This makes the early history and evolution of animals more, not less, interesting." Related Links: |
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