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Faculty Advisor

Noe U. de la Sancha

Abstract

Ontogeny is described as the history of an organism through its lifetime including development, growth, and allometry. The ontogenetic approach in cranial dimensions has proved useful in interpreting evolutionary patterns. Among the largest Didelphidae family of Neotropical marsupials, the species of Gracilinanus agilis and Cryptonanus chacoensis are poorly known. In this study, we address three questions; Is there sexual dimorphism in these species? What is the pattern of allometry? Which allometric patterns best describe the patterns in the skull and mandible? We applied geometric morphometrics to describe and test these differences using MorphoJ. A discriminant function analysis was performed to explore the comparisons between males and females on the ventral, dorsal, lateral, and mandible views of the skull. The analysis included the difference between means using the Mahalanobis and Procrustes distance, and permutation tests (n = 1000 permutation runs). Evidence of sexual dimorphism in G. agilis was not found, contrary to C. chacoensis where males and females differ the most at the parietal, occipital, and width of the temporal bones, the corpus, and three processes of the ramus. Age dimorphism was found in the cranium and mandible of both species, where the adults and juveniles differed the most in the parietal and occipital bones, the corpus, and the three processes of the ramus. In summary, we are closing the gap between two poorly understood species in South America. These findings will be important to better understand the ecology and evolution of these marsupials and other closely related species.

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