The hamster, a member of the cosmopolitan rodent family, was extremely successful and widespread. The compact built of this species suggests that it may have been a burrower, although some have also suggested an aquatic lifestyle. Numerous species of hamster are known and it is likely that there are many more yet to be discovered. It has been suggested that the word hamster may actually refer to a paraphyletic grouping of rodents, as the fossil record indicates that hamsters were found only in Western Asia for much of their history. It is quickly becoming accepted that hamsters, rather than undergoing a massive dispersal across the word, may actually be as many as twenty convergent rodents which all evolved from a mouse-like ancestor sometime during the late Holocene. The various hamster species all seem to have been generalists, eating anything they could find. There are even fossils of hamsters with what appear to be baby hamsters within their stomachs indicating that the hamster was a cannibal. This contrasts with previous ideas that rodents were social animals. Hamsters, like their rat relatives, appear to have been crepuscular or nocturnal and likely possessed excellent low light vision. They would wait in their subterranean burrows, sleeping during the day and using trapped heat to warm themselves out of their torpor at night. This is generally thought to be an adaptation to avoid cold blooded predators such as the jackal and lynx; which would become sluggish just as the hamster became active.
Mammals, traditionally, are thought to have been ectotherms. Some researchers propose that at least small mammals were endothermic and sported some sort of filamentous integument. It is also suggested that mammals may have had thicker deposits of fat than normally depicted to help insulate them in cold climates. Mainstream scientists consider this absurd as we all know the Cenozoic was an age of tropical swamps, rainforests, and hot deserts. The restoration on the right represents these new ideas; however unlikely they may be.