Amazonia as the Origin and Diversification Area of Didelphidae (Mammalia: Metatheria), and a Review of the Fossil Record of the Clade

Abstract

Didelphidae is the largest New World radiation of marsupials, and is mostly represented by arboreal, small- to medium-sized taxa that inhabit tropical and/or subtropical forests. The group originated and remained isolated in South America for millions of years, until the formation of the Isthmus of Panama. In this study, we present the first reconstruction of the biogeographic history of Didelphidae including all major clades, based on parametric models and stratified analyses over time. We also compiled all the pre-Quaternary fossil records of the group, and contrasted these data to our biogeographic inferences, as well as to major environmental events that occurred in the South American Cenozoic. Our results indicate the relevance of Amazonia in the early diversification of Didelphidae, including the divergence of the major clades traditionally ranked as subfamilies and tribes. Cladogeneses in other areas started in the late Miocene, an interval of intense shifts, especially in the northern portion of Andes and Amazon Basin. Occupation of other areas continued through the Pliocene, but few were only colonized in Quaternary times. The comparison between the biogeographic inference and the fossil records highlights some further steps towards better understanding the spatiotemporal evolution of the clade. Finally, our results stress that the early history of didelphids is obscured by the lack of Paleogene fossils, which are still to be unearthed from low-latitude deposits of South America.

Craniodental Morphology and Phylogeny of Marsupials

“…This estimate is also broadly congruent with the molecular node-dating analysis of Jansa et al (2014) and with the total evidence tip-and-node dating analysis of Beck and Taglioretti (2020); however, it is considerably younger than estimated divergence dates suggested by several other molecular studies, which have dated the last common ancestor of living didelphimorphians as having lived in the early Oligocene or Eocene (Steiner et al, 2005;Meredith et al, 2008b;Mitchell et al, 2014;Vilela et al, 2015). Our estimated divergence date is broadly congruent with the known fossil record of didelphids (recently reviewed by Beck and Taglioretti, 2020;Castro et al, 2021): the oldest probable (crownclade) didelphids described to date are from the early Miocene (Colhuehuapian SALMA, ~21.0-20.1 Mya; Goin et al, 2007a;Dunn et al, 2012;Castro et al, 2021). However, these specimens are highly fragmentary (isolated teeth only), and their affinities are correspondingly uncertain (Goin et al, 2007a;Beck and Taglioretti, 2020;Castro et al, 2021).…”

“…Our estimated divergence date is broadly congruent with the known fossil record of didelphids (recently reviewed by Beck and Taglioretti, 2020;Castro et al, 2021): the oldest probable (crownclade) didelphids described to date are from the early Miocene (Colhuehuapian SALMA, ~21.0-20.1 Mya; Goin et al, 2007a;Dunn et al, 2012;Castro et al, 2021). However, these specimens are highly fragmentary (isolated teeth only), and their affinities are correspondingly uncertain (Goin et al, 2007a;Beck and Taglioretti, 2020;Castro et al, 2021).…”