How has the biogeography of Gondwanan mammalian clades varied over deep time?

My proposed project will focus on resolving biogeographical trends in Gondwanan mammalian clades. Specifically, I will quantitatively compare the potential for marsupials and placentals to engage in intercontinental dispersal, which could explain their disjunct distributions. South America and Australasia were both adjacent to Antarctica until the Eocene, with many clades continuously dispersing between the three continents (e.g. Reguero et al. 2014, Goin et al. 2015). Thus, it is unlikely that significant physical barriers prevented marsupials and placentals from establishing a homogenous distribution across Gondwana. As such, my initial hypothesis is that mammalian dispersal across Gondwana was dictated primarily by the limitations of and interactions among ecological niches, establishing in turn a baseline from which the present-day distributions of marsupials and placentals originated. I will specifically test the following: A) I hypothesize that the dispersal of clades was facilitated by 'dispersal corridors' of more suitable habitat. To test for this, I will model the habitat suitability for marsupials and placentals in Australasia, South America and Antarctica during the Mesozoic and Cenozoic. B) I hypothesize that clades with greater niche breadths were those that could have dispersed more successfully between continents, and indeed those more capable of dispersing in the present-day. Consequently, I will examine how niche breadths of placentals and marsupial groups differ in Australasia, South America and Antarctica (e.g. Garcia-Navas and Rodriguez-Rey 2019). C) I hypothesize that Australasian marsupials have filled the entire range of niches occupied by placentals elsewhere. I plan to test for this, perhaps demonstrating in the process the extent to which marsupials have been ecologically excluded in South America and elsewhere. D) Finally, I hypothesize that marsupials generally show greater niche conservatism - a tendency for a clade to retain a consistent ecological niche (e.g. Crisp and Cook 2012) - explaining at least some limitations to their diversity and biogeography. Thus, I will compare niche conservatism in marsupials and placental clades.