Members of this family, the hedgehogs and gymnures, are perhaps the most similar of all extant mammals to the very earliest mammals. Erinaceid fossils, however, date back only to the Eocene, while their extinct ancestors, the Adapisoricidae, are known from the Cretaceous. The family is made up of 17 species grouped in 7 genera, and can be found in Africa, Eurasia, southeastern Asia and Borneo. Hedgehogs and gymnures range in size from that of a mouse to a small rabbit.
Erinaceids can be identified by their dental formula (2-3/3, 1/1, 3-4/2-4, 3/3 = 36-44), complete zygomatic arches (the jugal is present), eyes and ears of moderate size, and plantigrade foot posture. The anterior incisors in some species are enlarged, but not to the degree seen in their smaller cousins, the shrews. The upper molars are quadritubercular and appear bunodont; the lowers include well developed trigonids and talonid basins.
Hedgehogs (but not gymnures) are covered with sharp spines. Many species of hedgehogs can roll up into a ball, hiding all vulnerable areas of the body under the protective spines. Gymnures lack spines but when threatened, produce a foul smell. Erinaceids live under logs or in burrows that they dig. They eat a wide variety of foods, including invertebrates, reptiles (hedgehogs are curiously resistant to snake venom and other environmental toxins), carrion, roots, and fruits. Hedgehogs are active only at night, and some species hibernate in the winter. They appear to be facultatively heterothermic. Gymnures may be active during the day. Even though they are mainly terrestrial, erinaceids tend to be good climbers and swimmers. Most have one or two breeding seasons per year. In most species this is the only time adults associate, at other times they are solitary. The young are born with soft spines that quickly harden.
References and literature cited:
Nowak, R.M., and J.L. Paradiso. 1983. Walker's Mammals of the World, 4th ed., Vol. I. Baltimore, Johns Hopkins University Press.
Vaughan, T.A. 1972. Mammalogy. Philadelphia, W.B. Saunders Co.
Yates, T. L. 1984. Insectivores, elephant shrews, tree shrews, and dermopterans. Pp. 117-144 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.
Deborah Ciszek (author), University of Michigan-Ann Arbor, Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
having the capacity to move from one place to another.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate