(subclass Theria, infraclass Eutheria)
A cohort that comprises mammals possessing incisors that are ‘rootless’, i.e. they continue to grow throughout life and are worn away by gnawing. The cohort includes the orders Rodentia and Lagomorpha, presumed to have diverged from the insectivorous eutherian stock during the Cretaceous and subsequently differentiated into rodent and lagomorph forms; but similarities between the two orders may be superficial, implying no close relationship, so their inclusion in a single cohort is somewhat arbitrary.
Subjects: Zoology and Animal Sciences.