Reconstruction of the Ancestral Xenarthran Karyotype

Abstract

Xenarthra is the group of mammals that reunites anteaters, armadillos and sloths. According to the most recent phylogenetic schemes, Xenarthra is considered one of the four main supraordinal eutherian clades. This group, found in Central and South America, is considered especially important as it may be at the base of the eutherian tree. Although most cytogenetic studies in Xenarthra have been restricted to a few specimens and poor resolution techniques, recent chromosome painting analyses in some Xenarthra species resulted in important data regarding mammalian karyotypic evolution. An ancestral karyotype with 2 n =48 chromosomes has been recently proposed as ancestral to all Xenarthra. This complement is very similar to the 2 n =46 proposed as ancestral to all eutherian mammals, which may be a further indication of the basal phylogenetic position of Xenarthra in the eutherian tree. Key Concepts: Xenarthra is a Central and South American group of mammals represented by anteaters, armadillos and sloths. Xenarthra is phylogenetically important because of its likely basal position in the tree of eutherian mammals. In general, cytogenetic data on Xenarthra are restricted to a few specimens and to low resolution techniques. However, the recent use of molecular cytogenetics, namely chromosome painting, in Xenarthra has provided data that allowed the reconstruction of a hypothetical Xenarthra ancestral karyotype (XAK) with 2 n =48. The 2 n =48 XAK closely resembles the proposed ancestral eutherian karyotype (AEK) with 2 n =46, which further supports the idea that Xenarthra is basal to all eutherians.