According to a paleontologist from the University of Alberta, non-avian dinosaurs were likely on the decline long before the catastrophic asteroid impact in the Yucatan Peninsula 66 million years ago. This fascinating insight into the ancient narrative can be explored through a remarkable three-hour drive along the Red Deer River, encompassing three significant sites.
The foundation for this exploration stems from a 2021 study conducted by an international research team, which included input from Phil Currie. The study proposes that the dinosaurs’ failure to recover from the devastating asteroid impact was amplified by their inability to adapt to a changing environment.
Currie elaborates on the concept of gradual extinction, which emerged approximately four decades ago, soon after the widespread acceptance that a massive asteroid impact in Chicxulub, Mexico, was responsible for the swift and catastrophic annihilation of dinosaurs at the conclusion of the Cretaceous Period.
“Since then, some experts argue that there was no sudden catastrophe—considering it a misleading distraction—and posit that dinosaurs gradually died out due to other reasons, although they may have ultimately succumbed to the asteroid strike. Others believe the extinction happened rapidly,” he explains.
“In any case, Alberta plays a significant role in unraveling this mystery.”
Tracing a trail of gradual extinction
Currie, alongside a team led by Fabien Condamine from the Institute of Evolutionary Science of Montpellier, France, conducted a thorough analysis of 1,600 dinosaur fossils to examine speciation and extinction rates for six major dinosaur families found in Alberta: Ankylosauridae, Ceratopsidae, Hadrosauridae, Dromaeosauridae, Troodontidae, and Tyrannosauridae.
“Our findings indicate that these dinosaur families were indeed in decline, not over a short span of time in the last million years before extinction, but over a period of 10 million years that commenced 76 million years ago,” explains Currie.
This decline can be traced along the course of the Red Deer River, commencing from the heartland of Alberta’s Badlands—Dinosaur Provincial Park, situated southeast of Calgary. This remarkable location has yielded over 50 dinosaur species dating back 76 million years.
“It is difficult to conceive of an ecosystem today that could support 50 species of large animals, let alone 150 species of other vertebrates including mammals, birds, pterosaurs, lizards, snakes, turtles, and fish,” remarks Currie. “Undeniably, Dinosaur Provincial Park stands as one of the most fossil-rich sites for dinosaurs worldwide, if not the most.”
Continuing along Veterans Memorial Highway (H36), enthusiasts of the Cretaceous era journey upstream to the Drumheller region, which is stratigraphically approximately four million years younger than Dinosaur Provincial Park. Despite once hosting a diverse range of environments, paleontologists have unearthed only 30 dinosaur species in this area.
“You can observe rather significant changes over a relatively short distance (145 kilometers) and within a comparatively brief timeframe,” adds Currie.
A brief hour-long drive north along Highway 56, between the Red Deer River and the Rumsey Natural Area—an expanse that boasts Canada’s largest remaining undisturbed aspen parkland and highly productive waterfowl habitats—culminates the tour at Dry Island Buffalo Jump Provincial Park. The park’s fossil record represents the period immediately preceding the asteroid impact, spanning from 145 million to 66 million years ago, which is approximately 10 million years younger than Dinosaur Provincial Park. By the end of the Cretaceous period, a mere dozen dinosaur species persisted in Alberta.
“Here in Alberta, it becomes quite evident that the number of species experienced a significant decline during the last 10 million years of the Cretaceous period,” states Currie.
Declining diversity
Numerous theories circulate regarding the reasons behind the decline of dinosaurs, but Currie holds the belief that a climatic shift during the late Cretaceous played a significant role, rendering conditions less favorable for large animals.
“Large animals thrive in environments that are highly stable, with favorable climates and abundant and diverse food resources,” he explains. “However, when the climate begins to deteriorate, the diversity of plants declines, which, in turn, affects the diversity of animals, particularly larger ones.”
Currie further elucidates that during the Cretaceous period, North America was characterized by extensive inland seas that spanned from the Gulf of Mexico to the Arctic Ocean. However, the growth of mountain ranges in the western region eventually pushed the inland seas southward, while the resulting elevation of land obstructed the warm southern currents from flowing into the Arctic.
“This led to a more continental climate, which typically results in a reduction in animal diversity,” he states.
“I believe the asteroid impact was the final blow, but its impact would not have been as severe if it had occurred 10 million years earlier when dinosaurs exhibited much greater diversity.”
Source: University of Alberta