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.
Insectivores, members of the order Insectivora, are some of the smallest mammals in existence. Two hundred fifty of the three hundred fifty species of this order are shrews. Moles, tenrecs and hedgehogs make up the remainder. One of the largest members of this order, the solenodon (found in Cuba and Haiti) and some shrews secrete poison from a gland above their teeth to subdue prey. Although most insectivores eat insects exclusively, some prey on other invertebrates such as worms and small vertebrates. Insectivores are very beneficial to humankind because some consume up to three time their weight in insects per day.
The skulls of insectivores are often long and slender. The eye orbit is generally open posteriorly and the zygomatic arches (cheek bones) are reduced or absent. The teeth are generally primitive in structure and all teeth are rooted. The dental count is normally 44 to 48, with many variations.
The order Erinaceomorpha contains the single family of Erinaceidae, which is comprised of the hedgehogs and gymnures. The 17 species belonging to this order can be found in Africa, Eurasia, southeastern Asia and Borneo. This order was once considered part of the now obsolete order Insectivora.