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)

The fossil record plays a key role in reconstructing deep evolutionary relationships through its documentation of the early diverging stem groups leading to extant phyla. In the middle Cambrian Burgess Shale, two famously problematic worms, Odontogriphus and Wiwaxia, have recently been reinterpreted as stem‐group molluscs based on their shared expression of a putative radula and putative ctenidia in Odontogriphus.1 More detailed analysis of these fossil structures, however, reveals pronounced anatomical and histological discrepancies with molluscan analogues, such that they are more (...) reliably interpreted as primitive features of the superphylum Lophotrochozoa. In the absence of any obviously derived characters, Odontogriphus could be placed in the stem group of the Lophotrochozoa or on the stem of any of its constituent phyla, whereas the dorsal covering of chaetae in Wiwaxia identifies it as a stem‐group polychaete. Despite their close relationship, these two jawed, segmented worms could conceivably represent the early stages of two separate phyla. BioEssays 28: 1161–1166, 2006. © 2006 Wiley Periodicals, Inc. (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)