CONICET researcher describes the evolution of a group of marsupials that lived during the Paleogene

The study, which was recently published in Zoological Journal of the Linnean Society, was led by CONICET researcher Laura Chornogubsky who works at the ‘Argentine Museum of Natural Sciences “Bernardino Rivadavia”’ (MACNBR). The scientist analyzed a group of extinct marsupials that were first described by Florentino Ameghino in 1897. The study describes the evolution of polydolpides, their kinship relationship and a hypothesis about their extinction.

During the Paleogene, between 66 and 23 million years ago, the polydolopids inhabited southern South America, which includes Chile, Argentine Patagonia and the Antarctic Peninsula.

“It seems to be unthinkable that a marsupial -and most of the terrestrial mammals- could survive in this continent but at the time when the polydolopids lived there were large forests similar to the Andean-Patagonians, even compatible with warmer climates” Chornogubsky explains. The researcher;s hypothesis is that with the passage of time the temperature dropped, as did humidity, causing a desertification of the region where the group of marsupials evolved. According to this theory, the extinction of polydolopids could be related to climatic deterioration during the early Oligocene.

There are currently three hundred species of marsupials in the world, most of them in Oceania. The kangaroo and koala are the most popular specimens. Nevertheless, in Argentina twenty-five species are located, among which the opossums or weasels stand out. “In the past, South American marsupials were much more abundant than they are today, with hundreds of species of widely varying shape and size,” says Chornogubsky.

Despite the fact that the debate is still open, some of the hypotheses focus on the relationship of polydopids with Australian marsupials. This situation accounts for the complex relationships that could have been established millions of years ago when the world was divided into two supercontinents: “Towards the end of the Cretaceous and beginning of the Paleogene, 66 million years ago, the southern South America and the Antarctica were united. The polydolopids could have evolved in a large continental mass without having major barriers that isolate them. For this reason the current records of Antarctica show us remains of these groups,” says Chornogubsky.

From a phylogenetic analysis carried out on dental remains, the researcher managed to describe a genus and the three new species: Hypodolops, Hypodolops sapoensis, Amphidolops intermedius and Amphidolops minimus, respectively. Chornogubsky’s research piece showed advances on the understanding of the evolutionary history of marsupials, “studying the past to understand the relationships between living beings that we cannot see today,” concludes the scientist.