Dinosaurs were thriving until asteroid struck, research suggests | Dinosaurs

Dinosaurs would not have become extinct had it not been for a devastating asteroid impact, researchers say, challenging the idea that the animals were already in decline.

About 66 million years ago, during the Late Cretaceous period, a massive space rock crashed into Earth, triggering a mass extinction that wiped out all dinosaurs except birds. But some experts suggest dinosaurs were already in decline.

Now researchers say dating a rock formation in New Mexico casts doubt on that idea and suggests dinosaurs had evolved leading up to that fateful collision.

First author of the study from New Mexico State University, Dr. Andrew Flynn said: “I think based on our new study it shows that they are not heading towards extinction, at least in North America.”

Writing an article in Science magazineFlynn and colleagues reported how they dated a rock unit called the Naashoibito Member in the San Juan basin using two methods.

The first involved analyzing the ratio of two isotopes of argon within crystals found in the rock; thus the maximum age for its formation was determined. The second involved analyzing the alignment of magnetic particles within the material that forms the rock; this is a feature that reflects the direction of the Earth’s magnetic field at the time it was placed.

“The extinction event actually occurs in the middle of a fairly brief period of polarity,” said Flynn. [where Earth’s magnetic poles are] reversed.”

Taken together, the results suggest that the part of the Naashoibito Member where the youngest dinosaur fossils were found formed no more than 350,000 years before the mass extinction. “These are the last dinosaurs in southern North America,” said Flynn.

The team says the results show dinosaurs from that period were more diverse than previously thought. “There’s no uniform North American dinosaur fauna that really makes them prone to extinction,” said Flynn.

In fact, although there were some species common to the north and south of North America, including large predators such as T rex, there were also distinct differences; researchers suggest this reflects changes in climate.

Prof Steve Brusatte, a co-author of the study at the University of Edinburgh, said: “In the north there were standard duck-billed dinosaurs such as triceratops and edmontosaurus with large numbers of horns. But in the south there were duckbills with elaborate crests and, most striking of all, the huge long-necked sauropods.”

He noted that alamosaurus, a sauropod, was almost 30 meters (100 ft) long and weighed more than a Boeing 737.

“There’s no sign that these dinosaurs were in trouble, that anything unusual was happening to them, or that they were in long-term decline,” Brusatte said.

The perception that overall dinosaur diversity was decreasing before the asteroid impact may be due to the fact that exposed rocks, and therefore fossils, were fewer at the end of the Cretaceous period than at the early part of the period, Flynn said.

“Apparently, as far as we can tell, there is no reason for them to become extinct; [the] asteroid impact,” he said.

Prof Michael Benton from the University of Bristol welcomed the study. The palaeontologist, who was not involved in the study, said: “The new evidence of very late-surviving dinosaurs in New Mexico is very exciting and shows that faunas were diverse in at least one area.”

But Benton noted that the paper only looked at one location and did not represent the complexity of dinosaur species in North America or around the world at the time.

“As the authors show in the paper, the diversity of dinosaurs in the last 6 million years of the Cretaceous was generally less diverse, falling from 43 species previously to 30 species in western North America,” he said.

“We suggest that towards the end of the Cretaceous there is evidence for a general decline in the number of dinosaurs, with individual rich faunas for which the climates were suitable.”