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Scanning over the data in this table, it is clear that some groupings are indicated by several synapo-morphies, but there are contradictions. For example, the diapsid skull (see p. 447) supports a pairing of lizard and chicken, but warm-bloodedness suggests a pairing of chicken and mammal. Both pairings are not possible, and one of these synapomorphies must be wrongly interpreted. The method of testing at this point is to seek the most parsimonious pattern of relationships, that is, the one that explains most of the data and implies least mismatch, or incongruence. The data may be run through a computer program, such as PAUP (Swofford 2007) that finds the most parsimonious cladogram (Fig. 5.10a), and highlights the incongruent (i.e. probably misinterpreted) characters. The cladogram is of course a best effort, and further study of the specimens, and the discovery of new characters, can confirm or refute it.

The cladogram can be made into a phylogeny by the addition of a time scale (Fig. 5.10b). Here, the fossil evidence for dates of origin of the various groups is used to give a picture of the true shape of this part of the phylogeny of life.

Read more about cladistics in Forey et al. (1998), and about cladistics as applied to fossil organisms in Smith (1994). Cladistic software includes PAUP (Swofford 2007), the most-used program, and basic cladistic routines are available in PAST (Hammer & Harper 2005). Read more at http:// www.blackwellpublishing.com/paleobiology/.

1. fins

1. fins

4. bone

7. lungs or swim bladder 10. marginal teeth

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