A single fossilized footprint found in volcanic mud on a remote Antarctic island is the first known trackway from a mammal in Antarctica, and the earliest evidence anywhere on the continent of a carnivorous mammal.
Track-bearing slab T-373 from King George Island, Antarctica. Sclae bar – 10 mm. Image credit: Mansilla-Vera et al., doi: 10.1007/s00300-026-03539-1.
The new specimen, a partial hand-and-foot (manus-pes) print set, dates back to the Eocene epoch, some 55 million years ago.
Labeled T-373, it was collected from the Fossil Hill Formation on King George Island’s Fildes Peninsula.
This paleontological site is so rich in preserved plants, feathers and animal traces that it is protected as an Antarctic Specially Protected Area.
“Although the oldest mammalian or mammal-like footprints date from the Late Triassic, a remarkable increase in the diversity and abundance of their record occurs towards the end of the Mesozoic, together with direct evidence in the form of teeth and skeletal remains,” said Dr. Héctor Mansilla-Vera from the Instituto Antártico Chile at the Museo Colección Paleontológica de Antártica y Patagonia and his colleagues from Chila and Argentina.
“Following the Cretaceous-Paleogene mass extinction event, the fossil record of land mammals, including bones, teeth, and ichnological evidence, such as footprints, becomes markedly more abundant worldwide.”
“The mammalian fossil records from South America, which are phylogenetically linked to those from the Antarctic continent, clearly contrast with the much scarcer record documented there.”
“The complete land-mammal fossil record from Antarctica is represented mainly by isolated teeth and, to a lesser extent, by skeletal remains.”
“Notably, all these materials are restricted to Eocene-Oligocene layers on Seymour (Marambio) Island, West Antarctica, highlighting the strong geographic bias of the Antarctic Paleogene mammalian record in a continent where terrestrial mammals are now entirely absent.”
The T-373 print itself is small — about the size of a large coin — but its shape offers clues to who made it.
The specimen shows three rounded toe pads arranged in an arc, a triangular heel pad, and no claw marks, features consistent with a cat-sized mammal walking on its toes.
Using a formula that estimates body mass from footprint area, the authors calculated that the animal weighed only about 1.3 kg.
These size and shape closely match a group of extinct South American predators called sparassodonts, pouched, weasel-like mammals related to opossums that were common in Patagonia during the same era.
“T-373 represents the natural cast of a small, partially preserved manus and pes imprint, characterized by a rounded triangular metapodial pad impression, at least three circular digit impressions arranged in an anterior arch, and a digitigrade posture,” the paleontologists said.
“The estimated body mass for the T-373 trackmaker aligns precisely with the size range of small Hathliacynidae sparassodonts, e.g., Pseudonotictis.”
No fossilized bones or teeth from a sparassodont have ever been found in Antarctica.
But the researchers argue the footprint is the strongest evidence yet that these animals crossed into Antarctica over a land bridge that once connected the continent to South America, before the two landmasses drifted apart and Antarctica’s climate turned frigid.
Until now, palentologists believed the only land predators in Antarctica’s Eocene forests were small ancestors of today’s falcons and flightless terror birds.
The new find suggests mammals also occupied a predatory niche in that ecosystem, adding a previously unknown layer to the Antarctic food web.
“The T-373 footprint constitutes the first direct ichnological evidence of a land mammal in the Eocene ecosystems of Antarctica,” the scientists concluded.
“The discovery supports the idea that these endemic South American predators had reached high southern latitudes by the early Paleogene.”
“It further refines the reconstruction of the trophic structure of the West Antarctic ecosystem by revealing a more complex food web integrating herbivores, small mammals, birds, and now a mammalian apex predator within a transitional coastal environment.”
The discovery is reported in a paper published this month in the journal Polar Biology.
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H. Mansilla-Vera et al. 2026. First mammal tracks from the Eocene of Antarctica. Polar Biol 49, 101; doi: 10.1007/s00300-026-03539-1
