Evolution and systematics

Elephant shrews, or "sengis," are not shrews at all, despite their long inclusion by taxonomists within the order Insectivora, which does include shrews (family Soricidae). As of 2001, extensive genetic comparison studies, along with morphological studies, strongly support placing sengis in their own order, Macroscelidae, and family, Macroscelididae. Scientific and popular literature are now using the new common name "sengi," from Swahili so as to disassociate the species from the Soricidae shrews.

The same and related genetic and morphological comparison studies support the inclusion of several African mammal orders into the superorder Afrotheria: the sengis (order Macroscelidea); elephants (Proboscidea); manatees and dugongs (order Sirenia); hyraxes (order Hyracoidea); aard-varks (order Tubulidentata); and Afrosoricida (or Tenreco-morpha), including golden-moles (family Chrysochloridae) and tenrecs and otter-shrews (family Tenrecidae).

Although still a widespread, vigorous family of mammals, the glory days of the Macroscelididae were in the past, when there were many more species, including an additional four families. The 15 species that remain are but leftovers of an extensive pan-African radiation of sengis that began as far back as the Eocene Epoch, then peaked during the Miocene and Pliocene Epochs (24 to 2 million years ago [mya]). By 2 mya, all but the present living sengi species had become extinct.

Studies of the teeth of fossil and modern sengis indicate that the earliest ancestral sengis were primarily or exclusively consumers of plant material, some forms gradually changing over the ages to a more insectivorous diet. Present-day sen-gis eat only animal food, mostly invertebrates, or a combination of that and plant food.

The earliest known fossils in the sengi line are Chambius kasserinensis from the early Eocene of Tunisia and Herodotius pattersoni from the Late Eocene of Egypt (Eocene Epoch: 55 to 34 mya). The dental anatomy of these and other sengi fossils support (but do not confirm) a common ancestry of sengis with condylarths, primitive, extinct ungulate animals that gave rise to numerous lines of more recent and modern ungulates.

A bushveld sengi (Elephantulus intufi) at Kalahari Gemsbok National Park, South Africa. (Photo by Nigel J. Dennis/Photo Researchers, Inc. Reproduced by permission.)

There are two subfamilies within the single surviving family of Macroscelididae: Rhynchocyoninae, the giant sengis, with the single genus Rhynchocyon; and Macroscelidinae, the soft-furred sengis, with the genus Elephantulus and the monotypic genera Petrodromus and Macroscelides.

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