A molecular phylogeny of two extinct sloths

Xenarthra (Edentata) is an extremely diverse mammalian order whose modern r epresentatives are the armadillos, anteaters, and sloths. The phylogeny of these groups is poorly resolved. This is particularly true for the sloths ( phyllophagans), originally a large and diverse group now reduced to two gen era in two different families. Both morphological analyses and molecular an alyses of rDNA genes of living and extinct sloths have been used with limit ed success to elucidate their phylogeny. In an attempt to clarify relations hips among the sloths, DNA was extracted and mitochondrial cytochrome b gen e sequences were determined from representatives of two extinct groups of s loths (Mylodontidae and Megatheriidae), their two living relatives (two-toe d sloths [Megalonychidae], three-toed sloths [Bradypodidae]), anteaters and armadillos. A consistent feature of the latter two species was the nuclear copies of cytochrome b gene sequences. Several methods of phylogenetic rec onstruction were applied to the sequences determined, and the results were compared with 12S rDNA sequences obtained in previous studies. The cytochro me b gene exhibited a phylogenetic resolving power similar to that of the 1 2S rDNA sequences. When both data sets were combined, they tended to suppor t the grouping of two-toed sloths with mylodontids and three-toed sloths wi th megatheriids, The results strengthen the view that the two families of l iving sloths adapted independently to an arboreal lifestyle. (C) 2000 Acade mic Press.