Fossil organisms offer our only direct insight into how the distinctive body plans of extant organisms were assembled. However, realizing the potential evolutionary significance of fossils can be hampered by controversy over their interpretation. Here, as a guide to evaluating palaeontological debates, we outline the process and pitfalls of fossil interpretation. The physical remains of controversial fossils should be reconstructed before interpreting homologies, and choice of interpretative model should be explicit and justified. Extinct taxa lack characters diagnostic of extant clades (...) because the characters had not yet evolved, because of secondary loss, or because they have rotted away. The latter, if not taken into account, will lead to the spurious assignment of fossils to basally branching clades. Conflicting interpretations of fossils can often be resolved by considering all the steps in the process of anatomical analysis and phylogenetic placement, although we must accept that some fossil organisms are simply too incompletely preserved for their evolutionary significance to be realized. (shrink)

Paulin and Cahill‐Lane explore the origins of event processing and event prediction in animal evolution. They propose that the evolutionary benefit of being able to predict and thus to quickly react to anticipated events may have triggered the evolution of the earliest nervous systems.

The origin of chordates and the consequent genesis of vertebrates were major events in natural history. The amphioxus (lancelet) is now recognised as the closest extant relative to the stem chordate and is the only living invertebrate that retains a vertebrate‐like development and body plan through its lifespan, despite more than 500 million years of independent evolution from the stem vertebrate. The inspiring data coming from its recently sequenced genome confirms that amphioxus has a prototypical chordate genome with respect to (...) gene content and structure, and even chromosomal organisation. Pushed by joint efforts of amphioxus researchers, amphioxus is now entering a new era, namely its maturation as a laboratory model, through the availability of a large amount of molecular data and the advent of experimental manipulation of the embryo. These two facts may well serve to illuminate the hidden secrets of the genetic changes that generated, among other vertebrates, ourselves. (shrink)

A recent paper by Shu et al.(1) reinterprets the fossil Vetulicola and related forms, all from the Lower Cambrian, as basal deuterostomes, assigning them their own phylum, Vetulicolia. Their conclusion is based on the presence of structures resembling gill slits and a trunk‐like region that shows evidence of segmentation. This report summarizes the fossil evidence for their interpretation and evaluates a possible alternative, that vetulicolians may instead be tunicate‐like chordates. Implications for our understanding of the nature of the primitive deuterostome (...) (and chordate) body plan are discussed. BioEssays 24:208–211, 2002. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/bies.10064. (shrink)