Fossil discovery points to 'origin of modern world'

One of the most mysterious chapters in the Earth's history is being illuminated following the discovery of a massive trove of fossils in the US state of Colorado, researchers announced Thursday.

The find paints a clearer picture of how mammals and plants expanded after an asteroid struck the planet 66 million years ago, killing off the dinosaurs and wiping out three-quarters of all living species.

The skulls and bones of 16 mammal species were identified and are related to modern-day hoofed mammals like pigs, cows and deer. The fossils also consisted of pollen, leaf impressions and petrified wood.

The discovery points to "the origin of the modern world," said Tyler Lyson, an author of a paper reporting the fossil finds on Thursday in the journal Science.

"We just know so little about this everywhere on the globe," he said. "At least now we have at one spot a fantastic record."

The rise of the mammals

Scientists uncovered thousands of well-preserved plant and animal fossils at a site outside of Colorado Springs that show what life was like in North America before and after the asteroid struck.

Before the mass extinction, the area was a forest that was home to dinosaurs like the T. rex, while mammals were no bigger than 17 pounds (8 kilograms) or the size of small dogs.

Shortly after the asteroid struck off the coast of Mexico, the Earth entered a warming period and the area was blanketed with ferns, while the biggest animal in the post-apocalyptic landscape was the size of a rat.

Around 100,000 years after the impact, palm trees populated the forest and mammals were almost as big as they were before the asteroid hit, in what Lyson described as "a pretty rapid recovery."

With no dinosaurs around, mammals continued to grow. Some 300,000 years later, they were the size of large beavers. By 700,000 years after the mass extinction, the largest mammals were 100 times heavier than the mammals that survived the asteroid and were around the size of a wolf.

The first legume plants, like peas and beans, also appeared at that time.

'Biologic reset button'

The asteroid that led to the extinction of the dinosaurs was the second-worst mass extinction on the planet, but set in motion the evolutionary events that much later led to the rise of primates and eventually the appearance of Homo sapiens, or humans.

The worst mass extinction on record was one that occurred 252 million years ago that is believed to have been caused by extreme volcanism and paved the way for the first dinosaurs.

"Mass extinctions," Lyson said, "are the biologic reset button."

rs/rc (AP, Reuters)

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