Scientists have discovered the first direct evidence of a predatory land mammal in Eocene-era Antarctica — a tiny footprint, just two centimeters across, that reveals a hidden predator in the ancient polar food web.\n The track, described in a study published in Polar Biology, was found in the Fossil Hill Formation on King George Island in the South Shetland Islands. The footprint-bearing rock is estimated to be approximately 55.5 million years old, dating to the early Eocene when Antarctica was still connected to South America and covered in forests rather than ice.
The specimen, catalogued as T-373, consists of a partial footprint and handprint preserved as natural casts in fine-grained volcanic sediment. Despite its small size, it contains critical information: the track shows a digitigrade posture (walking on the toes), a compact metapodial pad, and at least three digital impressions arranged in an anteriorly convex arch.
Based on the footprint's preserved area, researchers estimated a minimum body mass of approximately 1.3 kilograms for the animal that made it. The combination of proportions, pad morphology, digit arrangement, and body size suggests the trackmaker was probably a small sparassodont metatherian — an extinct group of South American predatory mammals that occupied carnivorous niches during much of the Cenozoic era.
"The footprint is only about two centimetres long and wide, but it contains important information," the researchers wrote. "It provides evidence for a terrestrial mammal on King George Island, extends the known geographic record of Antarctic Paleogene mammals, and suggests that a small mammalian predator may have been part of the Eocene Antarctic food web."
The discovery is significant because Antarctica's land-mammal fossil record is remarkably sparse. Most known Paleogene mammalian remains come from Seymour Island and consist primarily of isolated teeth — remains that may have been transported by water rather than representing animals that actually lived on the continent. A footprint, by contrast, is direct evidence that an animal was physically present at the location where it walked.
During the early Eocene, Antarctica's high-latitude position did not mean extreme cold. Warmer climatic conditions and forested landscapes supported a terrestrial ecosystem that included mammals, birds, plants, and other organisms. Previous fossil discoveries had identified insectivorous, frugivorous, and herbivorous mammals, as well as large predatory birds known as "terror birds" (phorusrhacids). The new footprint adds a small mammalian carnivore to this picture.
The study also underscores how profoundly climate change has reshaped Antarctica. The Eocene–Oligocene transition, the establishment of the Antarctic Circumpolar Current, and the development of the Antarctic ice sheet ultimately drove land mammals to extinction on the continent. Today, no terrestrial vertebrates live in Antarctica.
The paper was published by Mansilla-Vera, H., de Valais, S., Goin, F., and Gelfo, J.N. in Polar Biology.
