75mya Glires (Rodents and Lagomorphs)

RATS, MICE, LEMMINGS, BEAVERS, SQUIRRELS.

Rodentia comprise the largest number of species in mammalia, more than 40 percent of all mammalian species. Members include rats, mice, lemmings, beavers, squirrels, etc.

Lagomorpha is a mammal order. It includes pikas, rabbits and hares. Although the lagomorphs look like rodents, they are not so, but are closely related to them. They have four incisors on the upper jaw, not two as in rodents. Also, they only eat plant material, not meat as rodents do to some extent.

Glires is the sister group to Euarchonta (which include tree shrews, cologus and primates) and thus, from a phylogenetic standpoint, a promising source of animal models for human research. An additional point in their favor is that they are easily bred under laboratory conditions. The rabbit was an important model of reproduction in a historic context and there has been a recent resurgence of interest, but lagomorphs have been overshadowed by rodents, especially the laboratory mouse. 

Recent developments of computer simulated models for research have reduced the number of rodents being bred for research and there are some groups working to eliminate them completely.  Rabbits are still bred and killed for their meat in many countries and other food animals from this group include Guinea pigs and capybara.