Index to Assignments Index to Assignment 1
Traditionally, the rodents have been divided into three sub-orders based on the comparitive physiology of their masseter (chewing) muscle:
However, the discovery of new fossils over the past fifty years have made this classification unsatisfactory; some rodents simply will not fit into the three-fold classification:
"The current status of rodent phylogeny is such that anyone can point out inconsistencies in anybody else's classification."
A.E. Wood (1966)(World authority on rodents)
One solution has been to retain the three original sub-orders and place the leftovers in a series of new sub-orders. Although untidy, this classification expresses with honesty the lack of knowledge concerning rodent relationships, and is open to adjustments as we learn more about the troublesome rodents.
Click here for an illustration of the rodent evolutionary tree according to comparitive physiology. The three basic sub-orders are highlighted in red. The new sub-orders are in black.
Last updated 2nd Apr '96