A single fossilized paw print, discovered in volcanic mud on a remote Antarctic island, represents the first known mammal track in Antarctica and the earliest evidence of a carnivorous mammal on the continent. The study’s findings were published in the journal Polar Biology.
The new specimen—a partial set of fore- and hind-paw prints—dates back to the Eocene epoch, approximately 55 million years ago.
Designated T-373, the specimen was found in the Fossil Hill Formation on the Fildes Peninsula of King George Island.
This paleontological site is so rich in preserved plants, feathers, and animal tracks that it is protected as an Antarctic Specially Protected Area.
“Although the oldest tracks of mammals or mammal-like animals date back to the Late Triassic, the end of the Mesozoic saw a significant increase in the diversity and number of such tracks, accompanied by direct evidence in the form of teeth and skeletal remains,” stated Héctor Mansilla-Vera of the Chilean Antarctic Institute (at the Paleontological Museum of Antarctica and Patagonia) and his colleagues from Chile and Argentina.
Following the mass extinction event at the Cretaceous-Paleogene boundary, the global fossil record of terrestrial mammals—including bones, teeth, and ichnological evidence such as paw prints—expanded significantly.
Fossil mammal discoveries in South America that are phylogenetically linked to finds from the Antarctic continent stand in stark contrast to the much more limited data documented in Antarctica itself. The entire fossil record of terrestrial mammals from Antarctica consists primarily of isolated teeth and, to a lesser extent, skeletal remains.
Notably, all these materials have been found solely in Eocene-Oligocene strata on Seymour (Marambio) Island in West Antarctica; this highlights a strong geographical bias in the Paleogene mammal record of a continent where terrestrial mammals are currently entirely absent.
The T-373 print itself is small—roughly the size of a large coin—but its shape offers a clue as to what made it.
The specimen exhibits three rounded toe pads arranged in an arc and a triangular heel pad, with no visible claw marks—features consistent with a cat-sized mammal moving on its toes.
Using a formula that estimates body mass based on footprint area, the authors calculated that the animal weighed only about 1.3 kg.
These dimensions and shape closely resemble those of a group of extinct South American predators known as sparassodonts—weasel-like marsupials related to opossums that were widespread in Patagonia during the same era.
“Specimen T-373 is a natural cast of a small, partially preserved manus or pes print, characterized by a rounded-triangular metapodial pad impression, at least three round toe impressions arranged in an anterior arc, and a digitigrade posture,” the paleontologists stated. “The estimated body mass of the T-373 track-maker aligns precisely with the size range of small sparassodonts from the family Hathliacynidae, such as Pseudonotictis.”
However, researchers argue that this footprint provides the most compelling evidence yet that these animals migrated to Antarctica via a land bridge that once connected the continent to South America, before the two landmasses drifted apart and Antarctica’s climate turned cold.
Until now, paleontologists believed that the only terrestrial predators in Eocene Antarctic forests were small ancestors of modern falcons and flightless predatory birds.
The new discovery suggests that mammals also occupied a predatory niche in this ecosystem, adding a previously unknown layer to the Antarctic food web.
“The T-373 footprint represents the first direct ichnological evidence of a terrestrial mammal in Eocene Antarctic ecosystems,” the scientists concluded. “This discovery supports the idea that these endemic South American predators had reached high southern latitudes as early as the beginning of the Paleogene.”
This allows for a more refined reconstruction of the trophic structure of the West Antarctic ecosystem, revealing a complex food web that integrated herbivores, small mammals, birds, and—now identified—a mammalian apex predator within a transitional coastal environment.
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