Dinosaurs were thriving in North America before the mass-extinction asteroid strike, study suggests

"Scientists have long debated whether dinosaurs were in decline before an asteroid smacked the Earth 66 million years ago, causing mass extinction. New research suggests dinosaur populations were still thriving in North America before the asteroid strike, but it's only one piece of the global picture, independent experts say. Dinosaurs were quite diverse and now we know there were quite distinct communities roaming around before being abruptly wiped out, said Daniel Peppe, a study co-author and paleontologist at Baylor University."

"The latest evidence comes from analyzing a portion of the Kirtland Formation in northern New Mexico that's been known for around 100 years to contain several interesting dinosaur fossils. Scientists now say those fossils and the surrounding rocks date from around 400,000 years before the asteroid struck, which is considered a short interval in geologic time. The age was determined by analyzing small particles of volcanic glass within sandstone and by studying the direction of magnetic minerals within mudstone of the rock formation."

Analyses of the Kirtland Formation in northern New Mexico show dinosaur fossils and surrounding rocks date to roughly 400,000 years before the asteroid impact at the end of the Cretaceous. Dating used volcanic glass particles within sandstone and paleomagnetic direction of magnetic minerals in mudstone. The fossils indicate diverse, distinct dinosaur communities lived regionally close to the extinction boundary. Differences between species in New Mexico and contemporaneous Montana sites argue against a broad, long-term North American dinosaur decline. The findings were published in Science and emphasize that North American dinosaur populations remained varied shortly before the mass extinction event.

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