The incisive foramen as character in distinguishing morphologically similar species of mammals

Abstract

An analysis of the morphology and variability of the size and shape of a key morphological structure in the rostral part of the skull—the incisive foramen—has been carried out. It is shown that incisive foramina are variable morphological structures, the features of which are group-specific (at the level of genera and families), and in some cases also species-specific. At both these levels, the shape and size of the incisive foramen have features that can serve as criteria for species identification by osteological patterns. Their location is important for diagnosis because these structures are preserved in most specimens that have suffered various kinds of damage (e.g. in fodder residues of carnivorous mammals or in owl pellets), and their placement in the anterior part of the bony palate as well as them being protected from the sides with rows of teeth makes these structures invulnerable to trauma-related variation. It is shown that there is a specific structure (size, location, and shape) of incisive foramina at the level of taxonomic groups of all ranks, from orders to species. The analysis was performed mainly on the examples of different groups of rodents as an order, represented by the largest number of pairs of close species. Examples with several different groups, in particular with different pairs of species of voles, mice, mole rats, ground squirrels, and others are considered. Examples with differences in close pairs of species in other groups (white-toothed shrews, polecats, roe deer, etc.) are also known. In all pairs of related species, a pattern was found, according to which species that are restricted to steppe ecosystems have the smallest incisive foramina, while species from wetland habitats have large ones. In many cases, groups of genera and families well differ in the shape and location of incisive foramina, and close pairs of species differ well in the size of these structures (primarily in length), although it is important to always consider the ontogenetic age of specimens: in young individuals, the incisive foramina are naturally small, similar to incisive foramina in other species, which are characterized by small incisive foramina in general. Based on the known data on the role of incisive foramina and the Jacobson organ in the life of mammals, hypotheses have been considered that may explain the differences in species and genera by the structure (size, location, and shape) of incisive foramina.