The evolution of the Canidae began in North America, as documented in Eocene sediments (40 Ma) with fossils of Hesperocyon (Wang et al., 2008). The vast North American fossil record strongly suggests that not only the origin but also the early diversification of canids took place on this continent. Successive radiation events soon gave rise to the three recognized subfamilies, Hesperocyoninae, Borophaginae and Caninae, by the late Oligocene (Wang et al., 2004). The first two subfamilies were endemic to North America and have been extinct since the middle Miocene and early Pleistocene respectively (Wang & Tedford, 2007; Wang et al., 2008). The sole surviving subfamily, Caninae, is now distributed worldwide and includes all 36 extant species of the family.
After being confined to North America for a period of about 30 Myr, canid lineages spread across the world. Members of the genus Eucyon reached the Asian continent through the Beringian land bridge around 6 Ma and continued on to colonize Europe (Wang et al., 2008). In South America, canid records are found much later, in late Pliocene sediments (ca. 3 Ma) (Wozencraft, 2005; Lucherini & Vidal, 2008). Despite the North American origin and the recent invasion, the largest extant canid diversity is actually found in the South American continent, with six genera and 11 species recognized (Wozencraft, 2005).
Extant canid diversity in South America certainly originated from more than one incursion from the north, given the presence of different lineages. Obvious representatives of North American species, such as the grey fox (Urocyon cinereoargentus) and the extinct Canis dirus, are found in South America (Berta, 1987; Prevosti & Rincon, 2007). The remaining assemblage of South American canids includes the so-called endemic fauna: the maned wolf (Chrysocyon brachyurus), the bush dog (Speothos venaticus), the crab-eating fox (Cerdocyon thous), the small-eared dog (Atelocynus microtis) and the South American foxes (Lycalopex spp.) (Wozencraft, 2005). The monophyly of the South American endemic fauna is well supported by molecular studies (e.g. Wayne et al., 1997; Lindblad-Toh et al., 2005), although some morphology-based phylogenies have included the Asian Nyctereutes procyonoides, the raccoon dog, within the group (Berta, 1987; Tedford et al., 1995).
Knowledge of the timescale of the evolution of the South American endemic fauna is critical to comprehend the history of the lineage. Nevertheless, most canid molecular studies focused solely on the phylogenetics of the group, neglecting divergence time issues (Bardeleben et al., 2005; Lindblad-Toh et al., 2005). The time of entry in the continent must be considered as important as a robust phylogenetic proposal if the scenario of canid diversification in South America is to be unveiled.
In this paper, we have attempted to reconstruct the evolutionary history of South American canids, establishing a chronological line for the cladogenetic events within the Canidae. In addition, in order to investigate the phylogenetic position of the canid fossils endemic to South America, we conducted a phylogenetic analysis that combines molecules and morphology for extinct and extant canid species.