Morphology, Paleontology, and Placental Mammal Phylogeny

Abstract

Placental mammals constitute the most intensively studied large clade of organisms. Deciphering their relationships has important implications not only to understand evolutionary processes (Bininda-Emonds et al., 2007) but also to inform many aspects of biomedical research (Springer and Murphy, 2007). Springer et al. (2007) have recently discussed limitations of morphological analysis of placental phylogeny compared with reconstructions based on molecular data. They presented a pessimistic view of the potential of morphological characters for use in high-level placental mammal phylogeny reconstruction, as the morphological data set they scrutinized (from Asher et al., 2003) does not recover the four major clades of mammals (Afrotheria, Xenarthra, Laurasiatheria, and Euarchontoglires) that these authors regard as overwhelmingly supported. In their contribution to the recurring debate on the “adequacy of morphology” (from their title), Springer et al. (2007) have provided empirical data to support their claims of the inadequacy of a morphological data set for resolving high-level mammalian phylogeny. Here, we would like to address several issues relevant to the arguments of Springer et al., including (1) their use of congruence of individual partitions to a “true” tree; (2) their generalization across morphological data sets based on their evaluation of one matrix; (3) their emulation of extinction as a heuristic tool; and (4) the role of paleontology and neontology in eutherian systematics. We end our commentary by discussing how “morphology” (comprising both paleontological and neontological characters) has not yet been fully exploited as a source of data for phylogenetic research.