| Paenungulata Temporal range: Eocene - Recent |
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|---|---|
| Elephants are the largest land mammals | |
| Scientific classification | |
| Kingdom: | Animalia |
| Class: | Mammalia |
| Subclass: | Eutheria |
| Superorder: | Afrotheria |
| (unranked): | Paenungulata |
| Orders | |
Paenungulata is a taxon that groups some remarkable mammals, including three orders that are extant: Proboscidea (including elephants), Sirenia (sea cows, including dugongs and manatees), and Hyracoidea (hyraxes, such as the African Rock Hyrax, Procavia habessinica). At least two more orders are known only as fossils, namely Embrithopoda and Desmostylia. Both of these extinct orders were as unique in their ways as the surviving orders. 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 terrestrial plants and had a posture similar to other large hoofed mammals.
Of the five orders, hyraxes are the most basal, followed by embrithopods; the remaining orders sirenians, desmostylians and elephants 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.
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 (tenrecs and golden moles), Macroscelidea (elephant shrews) and Tubulidentata (aardvarks).
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George Gaylord Simpson, using traditional taxonomic techniques, in 1945 succeeded in grouping these spectacularly diverse mammals in the superorder he named Paenungulata ("almost ungulates"). 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 odd-toed ungulates (Perissodactyla, such as horses and rhinos). 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. This would mean that paenungulates are not a clade.
Later, genetic techniques were developed for inspecting amino acid differences among haemoglobin sequences. 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 (Eutheria). The amino acid sequences do not support a connection with perissodactyls (odd-toed ungulates).