A new study mapping the evolutionary history of animals indicates that Earth's first animal--a mysterious creature whose characteristics can only be inferred from fossils and studies of living animals--was probably significantly more complex than previously believed.
The study, which was funded by the National Science Foundation (NSF), is the cover story of the April 10, 2008 issue of Nature. Using new high-powered technologies for analyzing massive volumes of genetic data, the study defined the earliest splits at the base of the animal tree of life. The tree of life is a hierarchical representation of the evolutionary relationships between species that was introduced by Charles Darwin. (See diagram.
Shaking Up the Tree of Life
Among the study's surprising findings is that the comb jelly split off from other animals and diverged onto its own evolutionary path before the sponge. This finding challenges the traditional view of the base of the tree of life, which honored the lowly sponge as the earliest diverging animal. "This was a complete shocker," says Dunn. "So shocking that we initially thought something had gone very wrong."
But even after Dunn's team checked and rechecked their results and added more data to their study, their results still suggested that the comb jelly, which has tissues and a nervous system, split off from other animals before the tissue-less, nerve-less sponge.
The presence of the relatively complex comb jelly at the base of the tree of life suggests that the first animal was probably more complex than previously believed, says Dunn.
While cautioning that additional studies should be conducted to corroborate his team's findings, Dunn says that the comb jelly could only have achieved its apparent seniority over the simpler sponge via one of two new evolutionary scenarios: 1) the comb jelly evolved its complexity independently of other animals, after it branched off ont
|Contact: Lily Whiteman|
National Science Foundation