What is it that defines an animal? The definition provided here, made on the basis of developmental biology, suggests methods for resolving phylogenetic problems.
REVIEWS I n recent years, considerable progress has been made in the field of molecular phylogen-etics. A significant driving force has been the increasing technical ease of DNA sequencing, which has led to the dominance of primary sequence data as indicators of the historical relationships between taxa. Important advances have also occurred in the… (More)
When and how did the mechanisms controlling regional identity in the vertebrate neural tube arise during evolution? The anatomy and embryology of the major deuterostome phyla (echinoderms, hemichordates, chordates) suggest that a true neural tube with dorsoventral and mediolateral regionalization arose with the chordates. We suggest that this was intimately… (More)
The chaetognaths, or arrowworms, constitute a small and enigmatic phylum of marine invertebrates whose phylogenetic affinities have long been uncertain. A popular hypothesis is that the chaetognaths are the sister group of the major deuterostome phyla: chordates, hemichordates, and echinoderms. Here we attempt to determine the affinities of the chaetognaths… (More)
Combining fields as diverse as comparative embryology, palaeontology, molecular phylogenetics and genome analysis, the new discipline of evolutionary developmental biology aims at explaining how developmental processes and mechanisms become modified during evolution, and how these modifications produce changes in animal morphology and body plans. In the… (More)