By Phil Myers
Almost all Mesozoic mammals were insectivorous. Insects are by far the largest group of organisms, both in terms of number of species and in biomass. They are marvelously diverse in habit and morphology. They provide a rich resource for anything that eats them, and their diversity alone suggests that their predators might exhibit similar variety. And so it is. Many mammals, including members of almost all orders, sometimes feed on insects. Members of one order, the Insectivora, feed almost entirely on invertebrates, especially insects. The Insectivora includes such groups as shrews, moles, hedgehogs, and tenrecs; these groups include around 375 species arranged in six living families. Tree shrews and elephant shrews have also sometimes been placed in this order; now, however, they are now classified separately (orders Scandentia and Macroscelidea, respectively). To complicate matters, recent research (Murphy et al., 2001) suggests that tenrecs and golden moles also do not belong in this group; rather, they should be classified with other African groups such as hyraxes, elephants, sea cows, aardvarks, and elephant shrews (the "Afrotheria"). For now, however, we leave them with the Insectivora.
What traits characterize members of the Insectivora? Most insectivores are small; shrews, for example, are among the smallest mammals. Most rely more on their senses of hearing, smell, and touch than on vision. Some shrews can echolocate. The part of the brain that houses the sense of smell is especially well developed. The ear region of insectivores lacks an ossified bulla. The tympanic membrane is attached to a bony tympanic ring, and the middle ear may be partially enclosed by processes from adjacent bones. The jugal is reduced or may be absent, and the zygomatic arch is sometimes incomplete. The cheek teeth of many are dilambdodont, and even those with more derived molariform teeth tend to have cusps that can easily be identified according to the tribosphenic pattern. The incisors of some Insectivora are enlarged (but they are reduced in others), and the canines also vary considerably in morphology. The eyes are usually very small, the feet are plantigrade and have five digits, and neither the hallux or pollex is opposable.
Many of the traits used to define Insectivora are probably primitive for mammals. Whether the order is a natural (monophyletic) group is still open to question.
Members of the order are found through much of the world. They are missing from Australia and all but the northernmost part of South America. Most species eat invertebrates.
Families included in the database
Literature and references cited
Murphy, W.J., E. Eisirik, S.J. O'Brian, O. Madsen, M. Scally, C.J. Douady, E. Teeling, O.A. Ryder, M.J. Stanhope, W.W. de Jong, and M.S. Springer. 2001. Resolution of the early placental mammal radiation using Bayesian phylogenetics. Science 294238-2351.
Vaughan, T. A. 1986. Mammalogy. Third Edition. Saunders College Publishing, Fort Worth. vii+576 pp.
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.
Contributors
Phil Myers (author), Museum of Zoology, University of Michigan.
