Featured Article Summary #153

Rodents are mammals from the order Rodentia, named for “gnawing.” They have one continuously growing pair of incisors in both the upper and lower jaws, and they make up about 40% of all mammal species. Rodents live on nearly all major landmasses except Antarctica and some remote islands, but many were later brought there by people. Most rodents are small, sturdy animals with short limbs and long tails, and they use their teeth to gnaw, dig burrows, and defend themselves. They can live in many different environments, including forests, underground areas, and even near or inside human spaces, and their social and breeding habits vary widely. Rodent fossils date back to the Paleocene, and they diversified strongly in the Eocene, spreading across continents and even reaching places like Australia. Rodents are identified by continuously growing, sharp incisors that wear down as they chew; enamel on the front and exposed softer back make the teeth stay chisel-shaped instead of growing into the skull. They have 12–28 teeth total, usually no canines, and a gap between the incisors and cheek teeth that helps with removing inedible bits; their molars are built for grinding, with strong jaw muscles that can’t gnaw and chew at the same time due to head shape. Rodents also tend to have strong senses (especially smell and hearing), often whiskers and cheek pouches, efficient digestion (including breaking down cellulose with gut bacteria and reusing nutrients by eating fecal pellets), and body features like sturdy bodies, flexible elbows, and varied tails and ways of moving; many species show differences between males and females in size that can vary by species and even by population. Rodents are found nearly worldwide, on every continent except Antarctica, and they are the only land placental mammals to reach Australia and New Guinea without humans. They can live in almost any habitat, from snowy tundra to deserts, including trees, underground burrows, and water, and they also do well in human areas like farms and cities. Besides sometimes being pests, rodents help ecosystems by spreading fungal spores and supporting plant–fungus partnerships, aerating soils and creating wetlands through species like prairie dogs and beavers. Most rodents eat mainly plants, but some are omnivores or even predators. Examples include field voles that eat grasses and gnaw bark in winter, pocket gophers that gather and store roots in burrows, and African pouched rats that collect food in cheek pouches before eating it. Some rodents also store large amounts of food for hard seasons, and many small rodents eat insects or other animals when available—some species are even specialized hunters. Many rodents live in groups, such as prairie dogs and brown rats, while others are more solitary, like hamsters and red squirrels. Solitary species may defend resources, whereas brown rats live in small colonies where males defend nearby territory; high crowding can change the social structure so males form dominance hierarchies, and females usually stay while males leave. Some rodents are highly cooperative: ground squirrels share protection and alarm calls, prairie dogs form large “towns” with territorial family groups, and naked mole-rats and Damaraland mole-rats live in eusocial underground colonies with one breeding female, while most others care for the tunnels, food, and young.