Recent Developments
That these groups of mammals are most closely related to each other has been questioned on anatomical and genetic grounds. Molecular phylogenetic studies have suggested that Perissodactyla and Cetartiodactyla are closest to Carnivora and Pholidota rather than to Pseudungulata.
Pseudungulata is united with Afrosoricida in the cohort or super-order Afrotheria based on molecular and DNA analysis. This means they are not related to other ungulates.
The orders of the extinct South American ungulates, which arose when the continent was in isolation some time during the mid to late Paleocene, are united in the super-order Meridiungulata. They are thought by some to be unrelated to other ungulates. Instead, they may be united with Afrotheria and Xenarthra in the supercohort Atlantogenata.
Embrithopods, desmostylians and other related groups are seen as relatives of paenungulates, thus members of Afrotheria. Condylarths are, as a result, no longer seen as the ancestors of all ungulates. Instead, it is now believed that condylarths are members of the cohort Laurasiatheria. So it seems that, of all the ungulates, only Perissodactyla and Artiodactyla descended from condylarths—assuming that the animals lumped by scientists into Condylarthra over the years are even related to one another.
As a result of all this, the typical ungulate morphology appears to have originated independently three times: in Meridiungulata, Afrotheria and the "true" ungulates in Laurasiatheria. This is a striking example of convergent evolution. This idea has met with skepticism by some scientists, because of the lack of an obvious morphological basis for splitting the ungulates into so many unrelated clades.
Read more about this topic: Ungulate
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