Arthropod Phylogeny And The Origin Of Tracheata (= Atelocerata) From Remipedia-Like Ancestors

This review summarizes some major events in the evolution of body plans along the backbone of the arthropod tree, with a special focus on the origin of insects. The incompatibility among recent molecular phylogenies motivates a discussion about possible causes for failures: there is a worrisome lack of information in alignments, which can be visualized with spectra of split-supporting positions, and there are systematic errors occurring even when using correct models in maximum likelihood methods (Kuck et al., this book). Currently, these problems cannot be avoided. Combining information from the fossil record and from extant arthropods, the morphology- based evolutionary scenario leads from worm-like stem-lineage arthropods via first euarthropods to the crown group of Mandibulata. The evolution of the man-dibulate head is well documented in the Cambrian Orsten fossils. The evolution within crustaceans is also the evolution that leads to characters of the bauplan of myriapods and insects. It is argued that morphologically myriapods do not fit to the base of the mandibulatan tree and that this placement is also not plausible from a paleontological point of view. Available morphological evidence suggests that myriapods are the sister-group to Hexapoda and that tracheates evolved from a marine ancestor that was similar in many ways to Remipedia. In the extant fauna, the Remipedia are the sister-group of Tracheata.