Marsupials are living mammals restricted to America (~75 species) and Australasia (~200 species). They are member of the Metatheria, a group including extinct forms and marsupials which is first represented in the fossil record in the Early Cretaceous. The main feature distinctive of marsupials is reproductive: they borne in an undeveloped state, and climb to the mother’s nipple where they remained attached for a long time. They show a variety of size ranging from ~100 mm in the smallest, to around 270 mm in the largest (in both cases including tail length). Species in this group have also a variety of diets with carnivorous forms eating insects and small vertebrates or in some cases middle-sized vertebrates. Omnivorous forms also include fruits in their diets. There are also strictly vegetarian species that eat leaves as is the case of several kangaroos and the koala, whereas the largest kangaroo and wombats have a diet based on grass.
Dorsal and lateral views of the skull of a juvenile (top), subadult (center) and adult (below) of the South American marsupial Caluromys lanatus.
Specimens from the American Museum of Natural History.
I am member of a research team formed by David Flores from the Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Buenos Aires and Norberto Giannini from the Universidad Nacional de Tucuman. We developed quali/quantitative studies of post-weaning cranial morphological changes in different species of extant marsupials. The basic methodology implies study of samples including different sizes (ages) of the same species. We explore qualitative changes by inspecting the cranial morphology represented in the smallest specimen of the sample and comparing with that of largest specimens (assumed to be adults). For the quantitative approach we record a series of cranial measurements in all the specimens of the sample and use these measurements for bivariate and multivariate analyses of allometry. In the frame of this project we already studied the ontogeny of four South American species: Didelphis albiventris, Lutreolina crassicaudata, Dromiciops gliroides and Caluromys lanatus, and one species from Australasia: Dasyurus albopunctatus. This research allowed the recognition of similar ontogenetic trends in species of different lineages of marsupials, as well as of ontogenetic modifications which are present in only some of the studied species. The future direction for this project is increase the number of species with similar kind of studies and finally provides a synthesis about ontogenetic changes and allometric variations represented in the skull of different lineages of marsupials.