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Fossils from La Brea Tar Pits show climate change drove evolution of ice age predators

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Climate change was a driving force in the evolution of some predators of the ice age such as the saber-toothed cat and the dire wolf, and the findings could yield clues to how modern animals will be affected by similar changes, researchers say.

Researchers examining fossils from the La Brea Tar Pits located in Los Angeles, including those of the ferocious dire wolf ancestors of today's wolves and the large-fanged felines, discovered significant changes in the properties and shape of the animals' skulls as the final ice age ended around 11,000 years ago.

During that time, researchers say, the climate was unstable, with rapid cooling and warming periods having a significant impact on the animals' evolution.

"When we compare fossils deposited at different times, we see big changes," Robin O'Keefe, the wolf study's lead author, said.

Dire wolves evolved to become smaller and more agile, adjusting to the predominance of smaller prey as the ice age ended, the researchers have reported.

Saber-toothed cats also went through an evolutionary change, says Julie Meachen from Des Moines University, lead researcher in a separate study on the large felines.

"Saber-toothed cats show a clear correlation between climate and shape," she says. "Cats living after the end of the ice age are larger, and adapted to taking larger prey."

The La Brea Tar Pits have long yielded fossil remains of both the cat and wolf predators and their prey, including mammoths and ground sloths.

Different tar pits at La Brea accumulated their fossil remains at different times, O'Keefe says, right up until the time humans appeared on the scene.

"We can see animals adapting to a warming climate at La Brea," he says. "Then humans show up and all the big ones disappear."

More research is needed to determine if the arrival of humans joined with climate change in the extinction of some La Brea species at the end of the ice age, he says.

"We haven't been able to establish causality there yet. But we are working on it."

Both O'Keefe and Meachen are research associates with the Page Museum, a satellite facility of the Natural History Museum of Los Angeles County located at the tar pits.

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