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.
