Dino Twist! Fossils Show the Giants Were Flourishing Moments Before Mass Extinction

A latest research shows that dinosaurs were still alive and well on the eve of extinction, as evidenced by a fossil site in New Mexico that contains many dinosaurs, including the enormous Alamosaurus, and dates to just before the asteroid strike that ended the dinosaur era.

The age of the fossils discovered at the Naashoibito site in northwest New Mexico has been disputed by paleontologists. The fossils date to approximately 340,000 years ago, which is a blip 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, according to the new study, which employed two dating techniques.

Except for their bird descendants, the disaster wiped out three-quarters of all species on Earth, including the dinosaurs.

The direction of Earth’s magnetic field at the time, as recorded in Naashoibito rock, served as the basis for one dating method. The other was determining how naturally occurring radioactive isotopes, which are elemental forms, decayed in sand grains that were embedded in the site’s rock.

Paleontologist Dan Peppe of Baylor University in Texas, one of the authors of the study published in the journal Science, said, “The age of the Naashoibito dinosaur faunas has been controversial for a long time, with some researchers suggesting that it was as much as 70 million years old, while others have suggested that it sampled the latest Cretaceous.”

The study offers the most recent data that challenges the long-held belief among paleontologists that dinosaur populations were declining globally prior to the asteroid impact.

Numerous dinosaurs from a variety of ecological niches can be found in the Naashoibito fossils near Farmington, New Mexico. At more than thirty tons and about one hundred feet (30 meters) in length, Alamosaurus was the largest of the plant-eating dinosaurs known as sauropods, which are distinguished by their long necks and tails as well as their four pillar-like legs.

Duckbilled dinosaurs, armored dinosaurs, and various bird-like dinosaurs are among the other Naashoibito inhabitants, along with the massive apex predator Tyrannosaurus and the horned dinosaur Torosaurus.

Fossils from the contemporaneous Hell Creek rock formation, which covers Montana, North Dakota, South Dakota, and Wyoming, were used in the study to show that the dinosaur community in the southern region of North America was different from that that exists further north on the continent.

Tyrannosaurus and Torosaurus were among the dinosaurs that these two communities had in common, but they differed in other respects and were clearly divided north-south. For example, sauropods were totally nonexistent up north, but Alamosaurus was a common resident at Naashoibito. Additionally, the southern duckbilled dinosaurs differed from the northern ones.

“This shows that dinosaurs were not a single homogeneous community spread across North America that was prone to extinction. Instead they were diverse and abundant leading up to the end of the Cretaceous,” Peppe added.

University of Edinburgh paleontologist and study co-author Steve Brusatte said, “They were doing what dinosaurs had been doing for over 150 million years, adapting to their local conditions, dividing up niches in the food chain, varying in size and shape and diet and exhibiting rich diversity across the landscape. There is no sign that these dinosaurs were in any trouble, or that anything unusual was happening to them, or that they were in any type of long-term decline.”

The last known sauropod dinosaur from North America, Alamosaurus, is also known from fossils discovered in Texas and Utah. It seems that it was only found in warm climates.

“Nothing illustrates how dinosaurs were thriving up to the very end more than the fact that Alamosaurus, one of the biggest dinosaurs ever – in fact, one of the very biggest animals to ever live on land in the entire history of the Earth – was there to witness the asteroid,” Brusatte said.

“So not only were sauropods still around when the asteroid hit, they were still thriving, still sublime, still colossal, still glorious,” Brusatte said. “I can imagine the scene: one minute, a jet plane-sized dinosaur was shaking the ground as it walked, the next minute the whole Earth was shaking with the energy unleashed by the asteroid.”