The cartilaginous nasal capsule of mammals becomes highly modified during ontogeny by resorption and ossification that finally results in the ethmoid bone. A deeper understanding of the early ontogeny of the ethmoidal region helps to elucidate morphological patterns and homologies in the adult cranium. However, the perinatal development of the ethmoidal region is not well studied though this is a craniogenetic crucial time frame. This is especially the case in the most species-rich rodent group, the Muroidea. In order to elucidate the perinatal transformation of the nasal capsule histological serial sections of 23 muroid species, one dipodid species, and two geomyoid species were investigated, some of which are represented by more than one ontogenetic stage. In addition adult crania of selected Muroidea were analyzed by µCT. The muroid grundplan of the ethmoidal region is already determined at birth and comprises a general pattern of six olfactory turbinals (two frontoturbinals, three ethmoturbinals, one interturbinal between the first two ethmoturbinals). Apomorphic patterns are restricted to the number of turbinals in the frontoturbinal recess: three in Abrothrix longipilis, one in Apodemus flavicollis, Apodemus sylvaticus, Micromys minutus, Mus musculus, and Rattus norvegicus . Perinatal stages of all altricial muroid species under study have a less mature ethmoidal region compared to precocial rodents e.g., caviomorphs. However, in muroids resorption of the nasal capsule and ossification of the turbinals, nasal septum and lamina cribrosa already start around birth and follow a distinct pattern observed in many other rodents. In around 14 days old stages of some investigated muroids the paries nasi and tectum nasi are almost completely resorbed except for the anterior nasal cartilages and those parts that become ossified and part of the ethmoid bone (e.g., roots of turbinals). Surprisingly, the precocial Sigmodon hispidus and Acomys sp. resemble generally the developmental pattern of altricial muroids although e.g., paries nasi resorption starts clearly earlier in Acomys. Furthermore, the perinatal maturity of Mesocricetus auratus that has the shortest gestation period among placental mammals corresponds to that of other altricial muroids. This observation supports an accelerated development in the golden hamster.

Acomys ; altricial; chondrification; ethmoid bone; Mesocricetus auratus ; nasal cavity; ossification; Peromyscus maniculatus ; precocial; Sigmodon hispidus ; turbinals