Reconstruction of the Ancestral Xenarthran Karyotype


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 2n=48 chromosomes has been recently proposed as ancestral to all Xenarthra. This complement is very similar to the 2n=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 2n=48.

  • The 2n=48 XAK closely resembles the proposed ancestral eutherian karyotype (AEK) with 2n=46, which further supports the idea that Xenarthra is basal to all eutherians.

Keywords: ancestral karyotypes; Eutheria; Xenarthra; mammals; chromosome evolution; chromosome painting

Figure 1.

Phylogenetic relationships of the extant xenarthran genera.

Reproduced with permission from Azevedo et al.2012. Drawings by Rosa Maria Alves Pereira. © BMC Evolutionary Biology
Figure 2.

Ancestral Eutheria karyotype (AXK). The numbers refer to the corresponding human chromosomes, which are represented by different colours. The chromosomes are drawn only roughly to scale.

Reproduced in part from Svartman 2012 with permission of S. Karger AG, Basel. © S. Karger AG, Basel.
Figure 3.

Diagram of the chromosomes of Ch. hoffmanni (2n=50), at the top, and of the ancestral eutherian karyotype with 2n=48, at the bottom. The numbers and colour code for the human chromosomes are the same as in Figure . In the bottom diagram, the numbers on the left of each ancestral chromosome represent the corresponding Ch. hoffmanni chromosomes. The asterisks and lines show the chromosomes that differ between the karyotypes of Ch. hoffmanni (CHO) and those proposed as ancestral (ANC) for Eutheria (CHO 14 and ANC 10q and 10p (black asterisks); CHO 13 and 19 and ANC 8q (green asterisks) and CHO 20 and 21 and ANC 7b/16p (red asterisks)).

Reproduced with permission from Svartman et al.2006. © BMC Evolutionary Biology
Figure 4.

Ancestral Xenarthra karyotypes (AXK) proposed in the literature. The complement at the top represents the AXK with 2n=54 (Liu et al., ) and the one at the bottom, the AXK with 2n=48 (Azevedo et al., ). The numbers and colour code for the human chromosomes are the same as in Figure .

Reproduced in part from Svartman 2012 with permission of S. Karger AG, Basel. © S. Karger AG, Basel.


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Further Reading

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How to Cite close
Svartman, Marta(Sep 2013) Reconstruction of the Ancestral Xenarthran Karyotype. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0024972]