One Saturday morning in 1982, Ascanio Rincón left half way through a football game with his friends to go to watch TV. He was only expecting to catch whichever National Geographic documentary was running, but what he saw that day changed the direction of his life.

"I watched this guy brushing off dirt from a skull in the most desolate landscape and right then I just knew," Rincón said of his first encounter with palaeontology. "I wanted to do that."

Three decades later, Rincón, 39, is one of a handful of palaeontologists working in Venezuela, and his findings have helped reframe scientists' idea of the Americas in the ice age.

Venezuela, rich in oil, is also rich in tarpits: pools of viscous asphalt where for millions of years seeds, birds or giant mammals have got stuck and died. Rincón's main excavation site at the moment is the Mene de Inciarte, a tarpit about half a mile wide, which lies in the Sierra de Perijá mountain range on the border with Colombia.

It is an inhospitable region, not least because it is a stronghold of Colombian guerrilla groups, but Mene de Inciarte has proved to be a jackpot of prehistoric remains: in just one cubic metre, Rincón and his team have excavated close to 16,000 specimens, ranging from microscopic seeds to fossilised bones.

Rincón lists his most significant findings with the contagious enthusiasm of a child reciting the cast of the Ice Age movies: the giant femur of a six-tonne mastodon, a giant ground sloth, a 10-ft pelican, caimans the size of buses and the almost intact skull of a sabre-toothed tiger.

"A famous palaeontologist used to say our work is a lot like hunting, except we resurrect rather than kill our game," Rincón said. "Seeing that tiger that no one else had ever seen before was like that. It gives you a thrill that only another palaeontologist can relate to."

The tiger or scimitar cat, Homotherium venezuelensis, has proved Rincón's most significant discovery so far because it pushes back the date, by more than a million years, by which time a wave of mega-fauna was originally thought to have appeared in South America.

"It showed us how little we understood of our palaeoenvironment and opened a wider window through which to take a look," said Rincón.

Traditionally, the view has been that animals migrated between the Americas through the Isthmus of Panama, in what is known as the great American biotic exchange, in seven significant waves. The scimitar cat – known to Rincón and his team as Richard Parker after the Bengal tiger in Yann Martel's novel Life of Pi – changes all this .

"Richard Parker tells us that there was an additional wave of migration that we knew nothing about. We now have to see what prompted it to arrive when it did," he said, referring to changes in climate or access to resources that might have caused the migration.

The answer to why these giant creatures disappeared could rest on one of his team's recent discoveries: arrowheads.

Their presence would mean that humans lived and hunted in the American continent earlier than thought. "We always find deposits of mega-fauna and, on occasion, we find arrowheads next to them," said Rincón. "We are still working on that."

For Rincón, studying the way the environment looked could help, among other things, to work out how much global warming is induced by humans and what aspects of it obey the natural rhythms of the planet.

"Life is cyclical – ours and the planet's. When you study modern ecosystems you're just looking at a snapshot. Palaeontology gives you the whole picture."