Metazoan evolution–a new model

Within their limits of resolution, different methods to reveal biochemical evolution appear to give reliable results where they can be controlled, as in the case of the Vertebrata. Compounds such as cytochrome c, SS rRNA and globins yield closely comparable results, which further strengthens the reliability. When the methods are applied to biochemical data from as many metazoan phyla as possible, the result is a phylogenetic tree which contrasts in certain respects with phylogenetic trees based on comparative zoology data. Important conclusions seem to include the following: (1) many metazoan phyla appear to have branched off from a shared, very conservative spiralian/protostome ancestral stock through the adoption of basically new feeding and locomotory strategies; (2) this origination makes it almost impossible to use a comparative zoology approach to solve problems of interphylum (in contrast to intraphylum) affinities, as similarities tend to be due only to shared derived Characters and similar life strategies, while dissimilarities are due to different basic life strategies; (3) protostome characters constitute a synapomorphy for triploblastic metazoans, and where absent they are secondarily lost, which means that protostome and deuterostome characters are irregularly distributed and mixed; (4) true deuterostomes form a sister group of the Mollusca, and they are only a top branch of the evolutionary tree.