Paenungulata
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| Paenungulata Fossil range: Eocene - Recent |
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 Elephants are the largest land mammals
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Paenungulata is a taxon that groups some remarkable mammals constituting three orders: Proboscidea (elephants), Sirenia (sea cows, including dugongs and manatees), and Hyracoidea (hyraxes, such as the African Rock Hyrax, Procavia habessinica).
All three still exist but at least two additional orders are known only as fossils, namely Embrithopoda and Desmostylia.
Both of these 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 creatures, the walking posture and diet of which have been the subject of speculation. However tooth wear indicates that desmostylians browsed on terrestrial plants and had a similar posture to other large hoofed mammals.
George Gaylord Simpson (1945), working with traditional taxonomic techniques, did succeed in grouping these spectacularly diverse mammals in the superorder he named Paenungulata ("almost ungulates"), but there were many loose threads in unravelling their genealogy. The hyraxes in his Paenungulata offered hints that they might be connected to the odd-toed ungulates (Perissodactyla) — horses and rhinos and kin. 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 this were so, then paenungulates would not be most closely related to one another.
Subsequently, genetic techniques were developed for inspecting the differences among amino acid differences among haemoglobin sequences. The most parsimonious cladograms depicted Simpson's Paenungulata as an authentic clade and as one of the most anciently diversified among the placental mammals (Eutheria): that is, among the first group to diversify from the basal placental mammals. The hypothetical connections with perissodactyls were not supported by the amino acid sequences, and although morphology continues to support the position of paenungulates with the rest of 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).
Of the five paenungulate orders, hyraxes are the most basal, followed by embrithopods, while 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.
[edit] Paenungulata Gallery
 A bull bush elephant |
 A manatee and her calf |
 The desmostylians are the only extinct order of marine mammals |
 The rhino-like embrithopods |
 The rodent-like hyrax |
[edit] References
- Simpson, G. G. 1945. "The principles of classification and a classification of mammals", in Bulletin of the American Museum of Natural History 85:1-350. (pdf version)
- McKenna, M. C., and S. K. Bell (editors). 1997. Classification of Mammals Above the Species Level. New York: Columbia University Press. ISBN 0-231-11013-8
