The treeshrews are small mammals native to the tropical forests of South and Southeast Asia. They make up the entire order Scandentia, which split into two families: the Tupaiidae (19 species, "ordinary" treeshrews), and the Ptilocercidae (one species, the pen-tailed treeshrew).
Though called 'treeshrews', and despite having previously been classified in Insectivora, they are not true shrews, and not all species live in trees. They are omnivores; among other things, treeshrews eat fruit.
Treeshrews have a higher brain to body mass ratio than any other mammal, including humans, but high ratios are not uncommon for animals weighing less than 1 kg (2 lb).
Among orders of mammals, treeshrews are closely related to primates, and have been used as an alternative to primates in experimental studies of myopia, psychosocial stress, and hepatitis.