Are the Fossil Data Really at Odds with the Molecular Data/ Morphological Evidence for Cetartiodactyla Phylogeny Reexamined

The phylogenetic position of Cetacea within the mammalian tree has long been a subject of debate. The traditional pale-ontological view is that an extinct order of mammals, the Mesonychia, is the sis-ter taxon to Cetacea (e.g., Van Valen, 1966; Prothero et al., 1988). This view has recently been supported by morphological studies that examined both fossil and extant ma-terial (Geisler and Luo, 1998; O’Leary and Geisler, 1999). The molecular evidence, by contrast, supports a phylogenetic hypothesis in which Cetacea is nested deeply within the Artiodactyla, implying that Artiodactyla is paraphyletic with respect to Cetacea (Sarich, 1985; Milinkovitch et al., 1993; Gatesy et al., 1999, and references therein). Furthermore, several molecular studies have suggested that hippopotamids are the sister taxon to Cetacea (e.g., Irwin and Arnason, 1994;