External morphology and chondrocranial development in therian mammals

FORASIEPI, A.M.; WERNEBURG, I.; SANCHEZ-VILLAGRA M.; HÜPPI, E.; TZIKA, A.C.

Greifswald

Jornada; 91st Annual Meeting Deutsche Gesellschaft für Säugetierkunde; 2017

Deutsche Gesellschaft für Säugetierkunde

Embryonicstaging of model organisms gives just a coarse picture of the varieties inexternal morphology of developing mammals. As opposed to traditional staging, we documented embryogenesisusing a standardized staging system, which serves to compare timing inorganogenesis analytically. Internally, placentals and marsupials revealmajor differences, exemplified in the shape of the developing cranium. Thebrain region represents a large portion of the head in a placental embryo,whereas the snout region with anterior oriented nares is relatively smaller. In contrast, in thepouch young of marsupials, the snout region is pronounced, whereas the brainoccupies a proportionally smaller space of the head. The nares are orientedlaterally and change shape during development. We hypothesized that functional requirements at the timeof birth shape the embryonic cranium of marsupials,and lead to apomorphicfeatures in the development of the anterior part of the chondrocranium, namely themouth region and nasal passage. To test this hypothesis and to address otherissues in comparative anatomy, we documented the development of the non-modelspecies Atelerix albiventris, Acomys dimidiatus, and Echinops telfairi (Placentalia) and Petaurus breviceps, Macropus eugenii, and Caluromysphilander (Marsupialia). We studied,using histological sections, the anterior part of the chondrocranium. Three-dimensionalreconstructions of the chondrocranium display derived disparity in chondrocrania proportions but conservatismin shape of the cupula nasi in marsupials. The diversity in external development is partly mirrored inchondrocranial developmental disparity. As such, both can, to a certain extent,serve as morphological proxy for one another through development.