Moeritherium

Moeritherium Temporal range: Late Eocene, 37–35 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Skeleton of Moeritherium at the National Museum of Nature and Science, Tokyo, Japan
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Proboscidea
Family:	†Moeritheriidae C.W. Andrews, 1906
Genus:	†Moeritherium C.W. Andrews, 1901
Type species
Moeritherium lyonsi Andrews, 1901
Species
†M. gracile C.W. Andrews, 1902 †M. trigodon C.W. Andrews, 1904 †M. andrewsi Schlosser, 1911 †M. chehbeurameuri Delmer et al., 2006

Moeritherium ("the beast from Lake Moeris") is an extinct genus of basal proboscideans from the Eocene of North and West Africa. The first specimen was discovered in strata from the Fayum fossil deposits of Egypt. It was named in 1901 by Charles William Andrews, who suggested that it was an early proboscidean, perhaps ancestral to mastodons, although subsequent workers considered it everything from a relative of manatees to a close relative of both clades' common ancestor. Currently, Moeritherium is seen as a proboscidean that, while fairly basal, predates the split between elephantiforms and deinotheres. Seven species have been named, though only three (M. lyonsi, M. gracile, and M. chehbeurameuri), are currently considered valid.

Moeritherium is unusual even among basal proboscidean standards. Like many later members of the group, it had two sets of tusks: the ones on the upper jaw pointed downwards, while those of the mandible (lower jaw) were flat and formed a spade shape. In addition to these trunks, it retained its upper canines, though had lost the lower set. The morphology of the skull, particularly the nasal cavity (which was only slightly retracted), suggests that Moeritherium lacked a trunk. It may have instead possessed a small, tapir-like proboscis, formed from the fusion of the upper lip and the nose, an evolutionary precursor of trunks. Though poorly described in the literature, Moeritherium's torso is known to have been very long, and its limbs were short. These divergent traits have led to comparisons with desmostylians, a lineage of extinct mammals formerly believed to have been relatives of manatees.

Moeritherium has been suggested to have led a semi-aquatic lifestyle. While this originally stemmed from perceived similarities to sirenians (manatees and dugongs), morphological data and isotope analysis has since lent it a great deal of support. The elongated body of Moeritherium, and the high position of its eyes and ears, are likely a result of its lifestyle, and its unusual dentition is likely an adaptation for feeding on water plants.