The End of Marsupials in the Americas: A Pleistocene Perspective

In the vast continent of South America, marsupials once thrived among unique and diverse ecosystems. However, the end of the Pleistocene saw the majority of these marsupial lineages become extinct. This article explores the extinction timeline of known marsupial species and their relatives, with a focus on those that barely missed the Pleistocene epoch.

Extinct Orders and Families

Some marsupial orders and families, such as Sparassodonta and Polydolopimorphia, came strikingly close to surviving into the Pleistocene. Sparassodonts, for example, were apex predators that coexisted with a range of other mammals, including marsupials and other placental mammals. However, these predators, like Thylacosmilus atrox, became extinct around 3.5 million years ago during the Chapadmalalan age.

Argyrolagus, a small, cute marsupial, also barely made it to the Pleistocene. Despite being much smaller and more herbivorous, this species persisted until the same period as Thylacosmilus. Polydolopimorphia, the order to which Argyrolagus belongs, had its heyday around 40 million years ago, yet it only just managed to survive into the middle Oligocene.

The Pleistocene and Marsupials

The Pleistocene epoch, spanning from 2.6 million to 11,700 years ago, saw a significant decline in marsupial populations in South America. By the time the Pleistocene began, placental mammals had already established a dominant presence, leading to the rapid decline of marsupials like sparassodonts. Other South American endemic groups such as litopterns, notoungulates, and ground sloths also faced extinction.

Marsupials in North America

While South America saw a major extinction event, North America also had its own marsupial lineages. Mammalian orders such as Herpetotheriidae and Peradectidae made it into the Miocene epoch, allowing a few species to survive into more recent times. The last herpetotheriid, Herpetotherium, disappeared around 17 million years ago in South Dakota, followed by the European species Amphiperatherium frequens about 13 million years ago.

Similarly, the last North American peradectid, Nanodelphys, became extinct around 23 million years ago in Nebraska. However, some European and Asian forms of peradectids survived slightly longer, indicating that marsupials coexisted with placental mammals for millions of years in different continents.

References

tGoin, F.J., and Pascual, R. (1987). News on the biology and taxonomy of the marsupials Thylacosmilidae. Anales de la Academia Nacional de Ciencias Exactas, Físicas y Naturales de Buenos Aires, 39, 219-246. tGoin, F.J., Abello, M.A., and Chornogubsky, L. (2010). Middle Tertiary marsupials from central Patagonia. In The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia (pp. 69–105). Cambridge University Press. tKorth, W.W. (1994). Middle Tertiary marsupials from North America. Journal of Paleontology, 68(2), 376-397. tJanis, C.M., Figueirido, B., DeSantis, L., and Lautenschlager, S. (2020). An eye for a tooth: Thylacosmilus was not a marsupial. PeerJ, 8, e9346.

The study of marsupial extinction in the Americas offers valuable insights into the complex evolutionary history of mammals. The persistence of a few species into the Pleistocene, albeit briefly, highlights the harsh environmental pressures that drove these unique taxa to extinction. Further research into these fascinating creatures continues to unravel the mysteries of their coexistence with placental mammals.