Almost 40% of the world’s mammals belong to the order Rodentia. These are not just rats and mice though. The order is divided into three suborders, the mouse-like rodents (Myomorpha), the squirrel-like rodents (Sciuromorpha) and the cavie-like rodents (Caviomorpha). The Myomorphs are by far the larger of the two groups, with about 1200 species in five families. The Sciuromorphs are divided into seven families and contain about 400 species and the Caviomorphs have about 200 species in 18 families. The largest of the rodents is the beaver, which can weigh in at up to 30 kg. The smallest is the African Pygmy Squirrel which is only 10 grams soaking wet. The most primitive of all living rodents is probably the Mountain Beaver, which is found in the American Pacific Northwest.
Rodents are found world-wide, in virtually every habitat, fill many different niches and eat just about anything. They evolved relatively recently with the earliest fossils known from about 25 to 40 million years ago and their diversity is related to their adaptablility. They have been extraordinarily adaptable to humans and have thus caused us a lot of grief. They eat our stored foods, live in our dwellings and spread diseases. Rat-borne diseases have probably killed more humans than wars and thus may have had a greater effect on history than most generals and tyrants. Science has paid them back by using rats, mice and guinea pigs in laboratories the world over to study and find cures for many diseases.
Suborder Sciuropmorpha
The majority of the squirrel-like rodents are indeed squirrels and belong to the family Sciuridae. There are about 270 species of squirrels which are adapted to living in trees in forests and woodlands. They are mostly seed eaters and the most common arboreal rodents, but there are also a number of ground-dwelling species. They are small, lithe and have long bushy tails, especially the tree dwellers.
The other families in this suborder share some primitive characteristics with the sciurids but are so different in other ways that this group may not be natural and may eventually be broken up. They include the beavers 3 species in two families, the Castoridae and the Aplodontidae), the pocket gophers (35 species, Geomyidae), the pocket mice (Heteromyidae, about 70 species), the scaly-tailed squirrels (7 species, Anomaluridae) and the springhare (Pedetidae).
Suborder Myomorpha
Most of the Myomorpha belong to the Old World rat and mice family, Muridae. Originally restricted to Africa, Europe and Asia, these are now found virtually everywhere, a few species having made it to even to remote islands by journeying there on ships. As well as rats and mice, this family contains the lemmings, voles and hamsters. There are four other families of mice: dormice (Gliridae and Seleviniidae), jumping mice (Zapodidae) and jerboas (Dipodidae). Arguably the ugliest rodent is the naked mole rat which belongs to the African mole-rat family.
Suborder Caviomorph
The cavie-like rodents include a variety of interesting families. The most well known are the new and old world porcupines, which are unique in having deadly spines for protection. The capybara is the largest rodent in this group. With it are numerous South American families, including true cavies or guinea pigs, coypu, hutias, pacarana, pacas, agoutis, chinchilla rats, spiny rats, chinchillas and viscachas, degus and tuco-tucos. The best known of these are the guinea pigs, which are a common food source in South America and which have been exported as pets to many other parts of the world.
This article can only touch on the incredible diversity found in the Order Rodentia. Many species have been little studied, especially the South American rodents. They are a highly successful group, having found niches on every continent except Antarctica. They are important in many food chains, providing food for numerous carnivores. Some even make good pets. While some have suffered at the hands of humans, others have adapted, survived and flourished. We might as well get used to them because rodents are here to stay.
