Paenungulata is a clade of "sub-ungulates", which groups three extantmammal orders: Proboscidea, Sirenia, and Hyracoidea. At least two more possible orders are known only as fossils, namely Embrithopoda and Desmostylia. Although morphological evidence continues to support the position of paenungulates with the ungulates, the molecular evidence suggests that Paenungulata is part of the cohort Afrotheria, an ancient assemblage of mainly African mammals of great diversity. The other members of this cohort are the orders Afrosoricida, Macroscelidea and Tubulidentata. Of the five orders, hyraxes are the most basal, followed by embrithopods; the remaining orders are more closely interrelated. These latter three are grouped as the Tethytheria, because it is believed that their common ancestors lived on the shores of the prehistoric Tethys Sea; however, recent myoglobin studies indicate that even Hyracoidea had an aquatic ancestor.
History
In 1945, George Gaylord Simpson used traditionaltaxonomic techniques to group these spectacularly diverse mammals in the superorder he named Paenungulata, but there were many loose threads in unravelling their genealogy. For example, hyraxes in his Paenungulata had some characteristics suggesting they might be connected to the Perissodactyla. Indeed, early taxonomists placed the Hyracoidea closest to the rhinoceroses because of their dentition, and even some recent evidence suggested a possible affinity of Hyracoidea to Perissodactyla rather than to the rest of the Paenungulata. If true, this would mean that paenungulates are not a clade. When genetic techniques were developed for inspecting amino acid differences among haemoglobinsequences the most parsimonious cladograms depicted Simpson's Paenungulata as an authentic clade and as one of the first groups to diversify from the basal placental mammals. The amino acid sequences reject a connection between extant paenungulates and perissodactyls. However, a :Image:Cooper et al. parsimony analyses consensus tree for anthracobunid phylogeny.png|2014 cladistic analysis placed anthracobunids and desmostylians, two major extinct groups that have been considered to be non-African afrotheres, close to each other within Perissodactyla.
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Extinct orders
Each of the extinct orders, the Embrithopoda and Desmostylia, was as unique in its members' ways of making a living as the three orders that survive. Embrithopods were rhinoceros-like herbivorous mammals with plantigrade feet, and desmostylians were hippopotamus-like amphibious animals. Their walking posture and diet have been the subject of speculation, but tooth wear indicates that desmostylians browsed on terrestrialplants and had a posture similar to other large hoofed mammals.
