Abstract
AbstractThe distinctly non‐random diversity of organismal form manifests itself in discrete clusters of taxa that share a common body plan. As a result, analyses of disparity require a scalable comparative framework. The difficulties of applying geometric morphometrics to disparity analyses of groups with vastly divergent body plans are overcome partly by the use of cladistic characters. Character‐based disparity analyses have become increasingly popular, but it is not clear how they are affected by character coding strategies or revisions of primary homology statements. Indeed, whether cladistic and morphometric data capture similar patterns of morphological variation remains a moot point. To address this issue, we employ both cladistic and geometric morphometric data in an exploratory study of disparity focussing on caecilian amphibians. Our results show no impact on relative intertaxon distances when different coding strategies for cladistic characters were used or when revised concepts of homology were considered. In all instances, we found no statistically significant difference between pairwise Euclidean and Procrustes distances, although the strength of the correlation among distance matrices varied. This suggests that cladistic and geometric morphometric data appear to summarize morphological variation in comparable ways. Our results support the use of cladistic data for characterizing organismal disparity.
Highlights
The distinctly non-random diversity of organismal form manifests itself in discrete clusters of taxa that share a common body plan
Given our small sample size and the fact that recognized monophyletic groups among caecilians are represented by very few taxa in our study, we opted for data set resampling to establish whether cladistic and geometric morphometric data produce: (1) similar relative disparities within subsamples; and (2) similar relative differences in disparity between two subsamples
Taxa are more dispersed in the plot based on Wilkinson’s revised cladistic data set (Wilkinson 1997; Fig. 1C), while analysis of the geometric morphometric data set (Fig. 1D) produces a clustering more similar to those obtained from the two alternative codings of the original data set
Summary
The distinctly non-random diversity of organismal form manifests itself in discrete clusters of taxa that share a common body plan. We use caecilian amphibians as an empirical case study of the extent to which geometric morphometric and discrete character data sets may be seen as ‘equivalent’ in terms of providing congruent inferences of patterns of disparity, as well as exploring the impact of character design and revision on analyses of organismal disparity.
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