Extract

This exchange stems from an on-going debate between advocates of crown clade (e.g., Gauthier et al., 1988; Rowe, 1988; Laurin, 1998) and those of apomorphy-based (e.g., Ahlberg and Clack, 1998; Lee, 1999; Padian et al., 1999; Anderson, 2001) definitions of widely used taxon names (see Table 1 for a glossary of terms). Both types of definitions have advantages: apomorphy-based definitions usually retain a composition of taxa similar to that proposed in most paleontological studies (Lee, 1999), whereas crown clade definitions correspond more closely to the usage of these names by comparative biologists working on extant taxa (de Queiroz and Gauthier, 1992; but see Bryant, 1994; Lee, 1996). Here, we concentrate on the name Tetrapoda, which has been the subject of recent discussion (Anderson, 2001, 2002; Laurin, 2002), but many of the arguments presented here could be applied to other widely used names, such as Mammalia, Aves, and Vertebrata.

Laurin (1998, 2002) adopted the crown clade definition of the name Tetrapoda (the last common ancestor of amniotes and lissamphibians, and all its descendants) proposed by Gauthier et al. (1988). Anderson (2002) objected to the crown clade definition of Tetrapoda and, following Lee (1999), advocated adoption of an apomorphy-based definition of this name (the first sarcopterygian to have possessed digits homologous with those in Homo sapiens, and all its descendants). The following exchange is aimed at clarifying the respective advantages of both types of definitions.

Associate Editor: Chris Simon
Chris Simon
Associate Editor
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