Paleocene Marsupials Demonstrate Social Behavior

Evidence of lifestyle and social behavior is almost never preserved in the fossil record. Now, a group of researchers from the Muséum national d'Histoire naturelle (Paris), CNRS (Paris) and Museo de Historia naturel Alcide d'Orbigny de Cochabamba (Bolivia) has excavated a remarkable collection of dozens of small mammal skulls and skeletons from the Tiupampa site in the central Andes in Bolivia that provides compelling fossil evidence of social behavior. A study of these remains, published this week in Nature, reveals the oldest example of group-living in mammals.

Today, many mammals live in groups. Others, such as most marsupials (which include the South American opossums and Australian koalas and wombats), are strictly solitary. We know very little about social behavior of fossil mammals, because only rarely is the number of preserved individuals large enough to provide evidence of community life.

Now, the discovery of a population of a mouse-sized ancient relative of marsupials (Pucadelphys andinus) from the early Tertiary (64 million years ago) in Bolivia demonstrates that group-living appeared early in the mammalian history, and may even represent the ancestral condition for mammals as a whole.

Basal synapsids have already been shown to be social, just an fyi.