Abstract

AbstractCladistic datasets of morphological characters are comprised of observations that exhibit varying degrees of consistency with underlying phylogenetic hypotheses, reflecting the acquisition and retention of character states (highly consistent characters), or the convergent evolution and loss of character states (less consistent characters). The consistency between phylogenetic history and individual character histories has a bearing both on the evolutionary process and on the relative ease with which phylogenetic history may be inferred from morphological data. We surveyed 486 tetrapod morphological cladistic datasets to establish an empirical distribution of consistency among characters and datasets. Average dataset size has increased in the number of characters and taxa through time. The Consistency Index measure of homoplasy decreases as more characters are added but the most significant decreases result from the addition of taxa. Retention Index and Homoplasy Excess Ratio remain relatively constant with changes in taxa and character number. Our sampling of larger datasets confirms that the positive relationship between dataset size and homoplasy is primarily caused by an increase in taxa, not an increase in characters. Genealogies of cladistic data matrices for early vertebrates, scalidophorans and crocodilians, which have been modified in succession, show a trend of generally consistent quality through research time. Thus, we find no support for the widely shared conjecture that in the search for phylogenetic resolution, high quality phylogenetic characters are quickly exhausted, with subsequent research leading to the inclusion of potentially misleading characters exhibiting high levels of homoplasy.

Highlights

  • This document is made available in accordance with publisher policies

  • Syntax Error: Invalid XRef entry ased our study on two published databases of morphological cladistic datasets (Wright et al 2016; Sansom et al 2018), for a total of 486 datasets, excluding a small number of MRP supertree matrices and categorical molecular datasets

  • To test the hypothesis that character consistency decreases over sampling time we identified three genealogies of matrices that are linked by successive modification based necessarily on our familiarity with the originating studies; this required extending our analyses beyond tetrapods

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Summary

Introduction

This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Cladistic datasets of morphological characters are comprised of observations that exhibit varying degrees of consistency with underlying phylogenetic hypotheses, reflecting the acquisition and retention of character states (highly consistent characters), or the convergent evolution and loss of character states (less consistent characters). Taxa can share superficially similar characters that are derived from separate ancestors and homologous characters can be absent as a consequence of loss, both of which contribute to the phenomenon of homoplasy which can misguide phylogenetic inference. When the proportion of homoplastic characters in a dataset is large, the homologous phylogenetic signal can be difficult to discriminate from homoplasy, resulting in recovery of an incorrect topology (Scotland & Steel 2015) that may, exhibit spuriously high statistical support in measures of phylogenetic fidelity, such as both the bootstrap or posterior probability (Philippe et al 2011).

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