Monophyly or polyphyly of the order Rodentia: Possible conflict between morphological and molecular interpretations

Abstract

Recent analyses of amino acid sequence data from selected proteins inCavia, Rattus, Homo, Bos, Sus, and a few additional rodents and other eutherians suggested that Rodentia is not a monophyletic taxon and thatCavia and other hystricognaths may have branched off earlier than the separation between Muroidea and Primates during mammalian evolution. Because this hypothesis of polyphyly is contrary to the otherwise unanimous recognition of rodent monophyly, we have reevaluated the morphological and developmental evidence from the cranium, dentition, postcranial skeleton, and fetal membranes for the taxa Hystricognathi, Muroidea, other Rodentia, Primates, Artiodactyla, and Lagomorpha, as well as for the eutherian morphotype. Our character analyses provide strong corroboration for the traditional hypothesis of rodent monophyly and lend additional support to the suggestion that Lagomorpha is the sister taxon of Rodentia. Our survey of published molecular data furnishes little or no support for the proposed hypothesis of rodent polyphyly. We conclude that this hypothesis is the result of poor sampling of sequence data from rodents and other eutherians, rather than any inherent difficulties in the use of molecular evidence for the assessment of mammalian evolution. The available molecular data suggest thatCavia differs considerably from other hystricognaths in many proteins, but the reasons for this remain to be investigated.