Introduction

Much has been written about the molecular revolution in phylogenetics and the ongoing conflict between molecules and morphology (Hillis 1987; Patterson 1987; Springer et al. 2004). With reference to therian mammals at least, the supposed conflict has been largely overblown: there is in fact general agreement between the two data sources, something unfortunately overshadowed by a handful of persistent ‘problem children’. The taxonomic content of most mammalian orders and other traditional higher-level taxa originally proposed purely on the basis of morphology has remained unscathed by the application of molecular sequence analysis. Even within these taxa, conflicts between molecular and morphological hypotheses of relationships are comparatively rare and usually relatively minor. For instance, a comparative study within Carnivora (Bininda-Emonds, 2000) revealed that most data sources and methods of analysis pointed at the same general solution, a few admittedly problematic taxa (e.g. Felidae) notwithstanding. In the end, the frequency and nature of disagreements over tree topology is arguably of the same order of magnitude within the separate spheres of molecular and morphological systematics as it is between them (Patterson et al. 1993). In many ways, the situation in mammals parallels that in vertebrates, where a fairly robust tree including gnathostomes, actinopterygians, sarcopterygians, tetrapods, amniotes and diapsids (among many other groups) has been supported by comparative anatomy since the 1800s (Asher and Müller, this volume).

Instead, many of the more celebrated conflicts in mammals tend to represent a lack of information, especially on the morphological side. The evolutionary tree of eutherian mammals presented by Novacek (1992), which exemplified the state-of-the-art morphological opinion at the time, is conspicuous today not for being very wrong (although some clades within it have been overturned by molecular information), but for its lack of resolution. Insectivora was long recognized to be a taxonomic wastebasket for any small brown mammal with sharp teeth that wasn't a rodent and couldn't fly.