Hoyo Negro
Inside Hoyo Negro, the underwater cavern where the skeleton was found. Roberto Chavez Arce

A 12,000-year-old human skeleton discovered nestling among the remains of mountain lions, sabre-toothed tigers and bears in an underwater cave in Mexico has revealed insights into how giant extinct species lived and migrated in the Americas.

Cave divers discovered what is thought to be the remains of the oldest and most complete early human skeleton found in the Americas. They descended the 55-metre flooded cave known as Hoyo Negro, or Black Hole, in the Yucatán Peninsula.

The hole acted as a trap for animals during the ice age, 13,000 years ago. Animals including mountain lions and tapirs as well as several extinct species including sabretooth cats, short-faced bears, an elephant-like gomphothere and a previously unknown species of giant ground sloth.

The layout is such that in the previous ice age, when sea levels were lower, the animals could walk comfortably along horizontal tunnels, only to find the cavernous and inescapable Black Hole at the end.

Cave palaeontologists from East Tennessee State University are presenting the findings on Saturday (26 August) at the annual meeting of the Society of Vertebrate Paleontology held this year in Alberta, Canada.

The find of the human skeleton – an adult woman – is perhaps one of the most exciting finds.

"This represents the oldest and most complete early human skeleton in the Americas, and she co-existed with a variety of megafauna," said Schubert.

"The preservation of the fossil material is extraordinary, and will allow us to reconstruct various aspects of anatomy, evolutionary relationships, and behaviour. The diversity of the fauna gives us an exciting new picture of this region in the midst of rapid climatic and environmental change," Schubert said.

The bones date from a period long after the Panamanian land bridge had formed, joining Central and South America about 3 million years ago. This allowed large animals to cross the bridge both ways, extending their range by thousands of kilometres.

The remains of the short-faced bear, a relative of today's spectacled bear, are a case in point of this migration of the American megafauna.

"The remains of the short-faced bear Arctotherium are particularly significant, representing not only the most complete and abundant material from one location, but also the first evidence that they crossed from South America into North America," Schubert said.