Cranial ontogeny of Lutreolina crassicaudata (Didelphidae): a comparison with Didelphis albiventris

Metatherians experience the greatest developmental changes during extrauterine life. Following previous studies on Didelphis albiventris Lund, 1840, we examined the postweaning cranial allometry of size of the Neotropical marsupial Lutreolina cras- sicaudata (Desmerest, 1804). Our aim was to compare growth patterns of both species to identify traits particular to each species and traits common to both species. This may contribute toward identifying a common developmental plan for didelphids. We mea­sured 15 cranial variables in 32-43 specimens from just-weaned young to old adult. Total length of the skull was the estimator of overall size in least squares and reduced major axis regressions. The skull of Lutreolina crassicaudata grows at a rate slower than the overall change in size in its neurocranial components, palate, and postcanine rows, and it grows relatively faster in the rest of the splanchnocranium. This pattern closely resembles that of Didelphis albiventris, from which it differs mainly in the allometry of the muzzle. In both species, allometry explains most postweaning changes of the trophic apparatus on functional grounds, in relation to interspecific differences in diet. We hypothesize that most local allometric departures from a generalized didelphid plan would relate to main dietary trends.