Intermolar palatal ridges in Norway rat (Rattus norvegicus) populations from 28 American cities - the configuration of the first ridge and prevalence of dark pigmented sections

摘要

The configurations of intermolar palatal ridges of 617 Norway rats ( Rattus norvegicus) from 29 discrete rat populations from 28 US cities were examined and compared with palatal ridge patterns of other rodent species of the genus Rattus. This detailed study of the intermolar palatal ridges confirmed that the first intermolar ridge ( I) has a distinguishing shape, which can be used as an aid in identifying Norway rats and revealed some minor morphological variations in shape, presence or absence of additional ridges, and occurrence of accessory denticles. Mammalian palatal ridges are generally flesh-colored; however, in these specimens an unusual feature was discovered, 13 of the 29 populations showed irregularly shaped, dark brown-pigmented parts of the intermolar ridges.