Since the days of Charles Darwin, researchers are interested in reconstructing the "Tree of Life", and in understanding the development of animal and plant species during their evolutionary history. In the case of vertebrates, this research has already come quite a long way. But there is still much debate about the relationships between the animal groups that made their apparation very early in evolutionary history, probably in the late Precambrian, some 650� million years ago. An international research group led by LMU Munich Geobiology Professor Gert Wrheide and colleagues from France and Canada has now managed to explain the relationships between some of these very early animal groups with a high degree of confidence. In the most comprehensive study of its kind, the researchers show that all sponges descended from a unique sponge ancestor, who in turn was not the ancestor of all other animals. That means that humans did not descend from a sponge like organism either, as some scientists have put forward. Moreover, the results also suggest that the nervous system only evolved once in animal history.
The most ancient animal groups (phyla) include the Porifera (sponges), Placozoa, Cnidaria, and Ctenophora (comb jellies). The sponges are extremely simply built, and have no organs. The placozoans also have a very simple structure. They have a flat, disk-shaped body, and no organs either. Comb jellies, the ctenophores, are life forms that resemble jellyfish. The true jellyfish, however, are part of the cnidarians, a phylum that also includes corals and sea anemones. The exact relationships among these early animal groups are still controversial, as different research groups have often obtained conflicting results. In particular, results from morphological studies, which look for structural similarities between different organisms, frequently contradict the results from molecular biological studies. The latter explore the functions of genes, and de
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| Contact: Luise Dirscherl dirscherl@lmu.de 49-892-180-2706 Ludwig-Maximilians-Universitt Mnchen Source:Eurekalert |
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