In terms of number of species, the mouse-like rodents are the most successful group of mammals alive today. The group is typically considered to consist of six families, with the vast majority of species crammed into just two - the mouse family itself, and the cricetids, which includes the voles and hamsters. These, however, are
relatively late arrivals, and there are two families that split from the main line of mouse-like rodents long before the ancestors of the mice and voles diverged from one another.
One of these consists of a grand total of three species (
maybe), living in the forests of southern Asia. The other goes by the technical name of the Spalacidae, and it consists of animals that have the rather unusual trait of spending almost their entire lives underground. There are at least 35 species of these animals, found in various places across Europe, Asia, and Africa. This is a fairly wide distribution, which raises the interesting question of how they managed to spread that far when they seem to have fairly narrow habitat preferences. Until recently, the evolutionary history of these oddities has been something of a mystery but now, it seems, we are starting to get enough information to piece together
an overview.