Metatheria versus eutheria: uma comparação trófica e morfológica

Abstract

The clade Theria has slept around 170 Mya into the two most diverse taxonomic groups of mammals: Metatheria e Eutheria. Since them, and especially during the Cenozoic, metatherians and eutherians followed towards very different evolutionary paths. Metatherians had a large portion of their evolutionary history restricted in South America and Oceania, while eutherians have dispersed and diversified throughout the whole globe. Nowadays, in South America, these two groups coexist at broad scale, frequently using the same natural habitat, like the didelphid marsupials and sigmodontine rodents. In the first two chapters of this document I present a comparison between didelphids and sigmodontines in relation to their trophic niche, using stable isotopes, and their scapular morphology. Both clades frequently occupy the same ecological and evolutionary space, culminating in overlapping patterns of trophic and morphological niche. On the one side, didelphids isotopic niche is smaller than that of sigmodontines. This is specially related to the higher amplitude of carbon enrichment of rodents, an indicative on the consumption of C4 and CAM plants within the trophic chain. On the other side, didelphids have more morphological disparity than sigmodontines in scapula shape, which is a consequence of the higher size variation among didelphids species and their intimate and strong relationship between shape and size. The large size variation of didelphids is also a good predictor of δ15N enrichment. In summary, larger didelphid species have higher levels of δ15N, indication increased consumption of proteins. In my third chapter, and at global scale, I investigate patterns of mandibular morphological disparity between mid and large sized Metatheria e Eutheria (> 7kg). Overall, patterns of morphological disparity in both clades are strongly correlated with paleoclimatic fluctuations through the evolutionary time. Moreover, the evolutionary restrictions that have been reported for methaterians does not seem to have kept them to achieve high levels of morphological disparity in mandibular shape, in which their disparity variables are comparable in magnitude to those observed in eutherians. Both clades have evolved highly adapted hypercarnivorous morphologies, showing convergent morphospace. Thus, in spite of their different evolutionary paths, I could identify several similarities between Eutheria and Metatheria, evolutionary convergences to similar habits that are not necessarily related to the same time period or geographical space.