In “Ancient Jelly Simplifies Animal Tree?” (The Scientist , September 9, 2011 Sabrina Richards reports “A newly discovered fossil of a nearly 600-million-year-old comb jelly ancestor may call for scientists to rethink early animal evolution.” Just think: 600 million years old. Well,
Like vertebrates, cnidarians exhibit bilateral or biradial symmetry—meaning they can be bisected into two mirror images. The ancestors of comb jellies, however, were not. The current version of the animal tree, which has the comb jelly lineage arising after bilateral cnidarians but before bilateral flatworms suggests that bilateral symmetry must have evolved twice—once in the cnidarian lineage, and again in animals that evolved after the comb jellies branched away. The new fossil, however, may shake up that view. According to the paper published recently in Evolution and Development, the new fossils of Eoandromeda would place comb jellies lower down on the tree than cnidarians, meaning bilateral symmetry would only have evolved once in the animal lineage—after comb jellies evolved.
Chalk one up for convergent evolution, whether anyone admits it or not, and that is more likely due to law or design than chance.
Comb jelly lights: