Fossilized Footprints Capture Prehistoric Man Hunting A Giant Sloth

An artistic recreation of the sloth hunt on the Alkali Flat playa. Matthew Bennett, Bournemouth University

At the tail end of the last ice age 11,700 years ago, a set of enormous mammals known as Pleistocene megafauna roamed Eurasia and North America alongside human tribes. However, without a written record or even a wealth of cave paintings like those found in Europe, researchers must examine a lot of indirect evidence in order to reconstruct what human-animal interactions were like shortly after the settlement of the Americas.

As such, it’s pretty exciting that an international group of researchers has uncovered more than 200 fossilized human and ground sloth footprints in the wilds of modern-day Utah that appear to have been formed during a hunt. In their subsequent analysis of the find, published in Science Advances, the authors estimated that the tracks, formed in hardened gypsum and silicate sands bordering the Alkali Flats in White Sand National Monument, were formed between 15,560 and 10,000 years ago.

The tracks at Alkali Flat. Matthew Bennett, Bournemouth University

Because animals evolve to be larger in cold climates, the chilly, 2.5 million year-long Pleistocene epoch produced towering specimens such as wooly mammoths, 3-meter-tall (10-foot-tall) bears, and car-sized armadillos. Though many of their smaller relatives survived, none of the megafauna species remained by the onset of a warm period some 8,000 years ago. The massive die-offs were likely not solely caused by the changing environment. Paleontologists have dug up a wealth of evidence suggesting that hungry hunter-gatherer groups, recently arrived across the land bridge and thrilled to find large, slow-moving prey, played a major role in the wipeout. 

(C) A circular mark made by a sloth reaching forward with its forelimbs and leaving knuckle and claw impressions. (E) Superimposed human and sloth track. Bustos et al./Science Advances, 2018

When these tracks were made, the large lake that previously covered the area had already evaporated, leaving an exposed, flat floor of sediment where water would have collected each wet season. It was into this damp soil that a 2.7- to 3 meter-long (9- to 10 foot-long) ground sloth – from either the Nothrotheriops or Paramylodon genus – appears to have wandered, with a human in pursuit.

According to the authors, the tracks indicate that the human was stalking the sloth, rather than passively following behind, because human tracks were made inside of the sloth’s immediately afterward, implying the walker adopted an uncomfortably long stride length in order to keep up. Moreover, once the human tracks appear, the sloth’s tracks begin to show “sharp direction changes that suggest evasion” and circular prints consistent with the sloth defensively rearing up on its hindlimbs.

“It is possible that the behavior was playful, but human interactions with sloths are probably better interpreted in the context of stalking and/or hunting,” the paleontologists wrote. “Sloths would have been formidable prey. Their strong arms and sharp claws gave them a lethal reach and clear advantage in close-quarter encounters.”


They conclude that the array of tracks could also represent a group of sloths being "collectively" harassed. Sadly, the actual outcome of this particular sloth-human showdown is lost to the ages.


  • tag
  • Pleistocene,

  • megafauna,

  • climate,

  • history,

  • early humans,

  • Clovis