WASHINGTON – A fossil site in New Mexico, rich with dinosaurs including the giant Alamosaurus, dates to before the asteroid impact that ended the age of dinosaurs, research shows. This underscores that these creatures were still thriving on the brink of extinction.
Paleontologists have long debated the age of fossils found at the Naashoibito site in northwestern New Mexico. The new study utilized two dating methods to determine the fossils are approximately 340,000 years old – a brief period in geological time – before the asteroid struck off the coast of Mexico’s Yucatan Peninsula 66 million years ago at the end of the Cretaceous Period.
The impact wiped out three-quarters of Earth’s species,including all dinosaurs except for their bird descendants.
One dating technique analyzed the direction of earth’s magnetic field at the time, as recorded in the Naashoibito rock.The other measured the decay of naturally occurring radioactive isotopes within sand grains embedded in the site’s rock.
“The age of the Naashoibito dinosaur fauna has long been controversial, with some researchers estimating its age at 70 million years, while others estimated samples dated to the late Cretaceous period,” said paleontologist dan Peppe of Baylor University in Texas, a study author published in the journal Science.
The study provides further evidence against the once-popular idea among paleontologists that dinosaurs were experiencing a global population decline before the asteroid impact. The Naashoibito fossils, discovered near Farmington, New Mexico, represent a diverse range of dinosaurs and ecological niches. The largest was Alamosaurus, weighing over 30 tons and reaching 100 feet (30 meters) long – one of the largest sauropods, known for their long necks, tails, and pillar-like legs.
Other inhabitants of Naashoibito included the apex predator Tyrannosaurus, the horned Torosaurus, as well as duck-billed, armored, and various bird-like dinosaurs.