The dinosaurs may have already been going extinct before the cataclysmic space rock hit Earth, new findings suggest

dinosaur asteroid meteor
An artist’s depiction of the moment the Chicxulub asteroid struck present-day Mexico 66 million years ago.

It’s tempting to ponder what life on Earth might have looked like had a space rock not hit 66 million years ago. That impact in present-day Mexico doomed the dinosaurs and a majority of land and marine species. In its absence, would humans and other mammals have eventually duked it out with T. rex and triceratops?

The answer is probably not, according to a study published Tuesday.

That research found that six major groups of dinosaurs were slowly going extinct over the 10 million years prior to the crash. The impact’s consequences – mile-high tsunamis, raging fires, and a choking cloud of thick dust and sulfur that blotted out the sun – were merely a nail in the dinosaurs’ coffin.

“The meteorite is seen as a coup de grĂ¢ce for dinosaurs, which finished them off,” Fabien Condamine, a research scientist at the University of Montpellier in France who co-authored the new study, told Insider.

Condamine and his collaborators suggest that a period of global cooling may have contributed to a decline in the overall number of dinosaur species, which then made it impossible for the animals to recover after the cataclysmic event.

“Many paleontologists think dinosaurs would have continued to live if the asteroid did not hit Earth. Our study brings new information for this question, and it seems that dinosaurs were not in good shape before the impact,” Condamine said.

Dinosaurs were already on their way out

T. rex
A full-grown Tyrannosaurus rex weighed between 6 and 9 tons and was up to 43 feet long.

The researchers behind the new study looked at 1,600 fossils from 247 dinosaur species that lived during the late Cretaceous period – from about 100 million to 66 million years ago. That group includes two-legged carnivores like the T. rex, triceratops, and duck-billed dinosaurs.

The team grouped them into six large families, then analyzed how the diversity of species in those families changed over time. The results show that across all six groups, the number of species started to gradually decline 76 million years ago, prior to the space-rock impact.

“We do not find that dinosaur diversity was high and diversifying toward the end of the Cretaceous, as previously thought,” Condamine said.

His isn’t the first group of scientists to suggest that dinosaurs actually went extinct gradually. A 2016 study found that as species of dinosaurs that had been around on Earth a while went extinct, no newer species replaced them. Although questions lingered as to whether that conclusion was simply the product of an incomplete fossil record, this new study shows that older species did indeed have higher extinction rates than younger ones.

An herbivore monopoly

Arctic dinosaur hadrosaur
A painting of Ugrunaaluk kuukpikensis, a species of duck-billed dinosaur that lived during the Cretaceous period.

In the late Cretaceous period, the planet began to cool: Starting 80 million years ago, global temperatures dropped by about 13 degrees Fahrenheit (7 degrees Celsius).

Given that dinosaurs relied on the temperature of their environment to regulate their body heat, Condamine said, that change in climate might have played a role in their extinction rates.

“Warm periods favored dinosaur diversification whereas cooler periods led to enhanced extinctions,” the study authors wrote.

Another possible explanation for the dinosaurs’ decline is a change in the number of herbivore species in the ecosystem. Hadrosaurs, or duck-billed herbivores, seem to have dominated between 76 million and 66 million years ago – out-competing their fellow leaf-eaters like triceratops and the clubbed-tailed, armored ankylosaurs. That contributed to the decline of those other herbivores.

“Removing herbivores can make the entire ecosystems more prone to extinction cascades,” Condamine said.

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T. rexes liked to walk as slowly as humans do – at a leisurely 3 miles per hour, a new study finds

The skeleton of a T. rex named Trix at Naturalis Biodiversity Center in the Netherlands.

For all the awe Tyrannosaurus rex inspires, the “king of the dinosaurs” wasn’t very speedy.

Paleontologists already knew this predator was slow: It could only reach a maximum speed between 10 and 25 miles per hour. A 2017 study suggests that if a T. rex went any faster than 12 mph, the predator’s bones would have shattered – so it walked quickly to pursue its prey when needed.

But according to a study published Wednesday, T. rexes didn’t like walking fast if they could help it.

The researchers calculated that the dinosaur’s preferred walking speed was a 3-mph stroll.

That’s just under the average preferred walking speed for a human. So you could probably out-walk a T. rex, or at least keep up with one during its evening jaunt.

“Humans and T. rex would not, if the study is right, have had very different walking speeds,” John Hutchinson, an evolutionary biomechanics expert at the Royal Veterinary College in London who was not involved in the research, told Insider.

T. rexes preferred walking at the same speed that elephants do

myths about dinosaurs jeff goldblum jurassic world dinosaur trex
Jeff Goldblum in front of a model dinosaur to promote “Jurassic World: Fallen Kingdom” in London, England.

An animal’s preferred walking speed enables it to move about using the least amount of energy possible, according to Pasha van Bijlert, the new study’s co-author.

While it may seem like the slower you walk, the less energy you use, that’s not necessarily the case. The best way to achieve maximum energetic efficiency is by finding a locomotion sweet spot known as resonance.

Imagine you’re swinging on a swing, trying to get it moving by swaying your legs back and forth. If you sway too quickly or too slowly, nothing happens. But undulating at just the right rhythm gets your body parts to resonate, and swing most efficiently.

A similar resonance happens when you’re walking at your preferred speed and your body finds a natural step rhythm.

“Many animals have a roughly similar preferred walking speeds: ostriches, elephants, giraffes, horses, gnus, and gazelles are the animals we’ve found data for, and they’re all not that fast when they don’t have to be,” van Bijlert told Insider. These animals prefer to walk between 2.2 and 3.1 mph, just like T. rex – and just like us.

jurassic park t rex
A shot from the 1993 movie “Jurassic Park.”

That means the iconic scene from the 1993 film “Jurassic Park,” in which a T. rex chases a group of park visitors driving away, isn’t very accurate.

“I don’t think anybody believes a T. rex could outrun a Jeep, but it sure does make for a good movie,” van Bijlert said.

T. rex’s tail helped it walk efficiently

Researchers previously calculated T. rex’s walking speed by looking at fossilized footprints, then using the distance between those tracks to estimate the length of the dinosaur’s stride. Those earlier estimates suggested T. rex could walk as fast as 6.7 mph.

But instead of focusing on what T. rex’s legs were doing, van Bijlert’s group looked at the predator’s tail. A T. rex’s tail bobs up and down as it walks.

According to the study authors, every time T. rex’s tail sways up, ligaments inside the tail pull its legs backward, and store energy that then gets released when the tail swings back down. That energy propels the dinosaur forward.

The pace of that tail sway indicates T. rex’s natural step rhythm.

T.rex illustration
A depiction of a full-grown Tyrannosaurus rex.

To figure how fast a T. rex tail would move, van Bijlert’s team created a 3D-model of an adult T. rex skeleton named Trix from the Naturalis Biodiversity Center in the Netherlands. The team reconstructed where all of Trix’s muscles and ligaments would start and end between her tail and legs, and used that model to help calculate her preferred walking speed: 2.9 mph.

Hutchinson said there’s some uncertainty around that result, however, because van Bijlert’s group didn’t take into account whether Trix’s tail would also be swinging side-to-side, and whether the muscles driving that motion might impact her top walking speed.

The new study doesn’t offer further insights into T. rex’s maximum speed, he added.

“There’s a big difference between a casual stroll in no rush versus a sprint,” Hutchinson said.

It would take an adult T. rex more than 13 hours of walking to patrol its territory

T. Rex’s preferred walking speed could tell us how long it took for the dinosaur to forage or scout an area, according to van Bijlert.

A new study from paleontologists the University of California, Berkeley suggested a single adult T. rex lived in an area roughly 40 square miles in size. So if a T. Rex went on a stroll to survey every part of its territory, the endeavor could take more than 13 hours.

t rex
A model of an adult T. rex on display at the American Museum of Natural History in New York City.

T. rex was still a deadly predator, though, when moving at maximum speed.

A fully-grown T. rex was one of the largest carnivorous land animals that ever walked the Earth, standing about 12 to 13 feet tall at the hip and measuring up to 43 feet from tooth to tail. An adult T. rex could weigh between 5.5 and 9 tons – about the size of an adult African elephant.

T. rexes also had a keen sense of smell, acute vision, and excellent hearing, making it hard for prey to avoid detection. On top of that, their jaws had a bite force of 7,800 pounds, equivalent to the crushing weight of about three Mini Cooper cars. No other known animal could bite with such force.

“All evidence suggests it would have no issues capturing similar-sized prey,” Hutchinson said.

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A whopping 2.5 billion fully grown T. rexes walked the Earth in the course of the species’ existence, paleontologists found

Jurassic Park T Rex
A T. rex depicted in the 1993 film “Jurassic Park.”

An adult Tyrannosaurus rex required a lot of space – and the prey therein – to survive.

According to new calculations from paleontologists the University of California, Berkeley, each adult T. rex lived in an area roughly 40 square miles in size.

The study, published Thursday in the journal Science, uses that math to offer an estimate of the total number of these predators that walked the Earth during the Cretaceous Period, between 66 and 68 million years ago: an impressive 2.5 billion.

“The total number did catch me off guard,” Charles Marshall, a paleontologist at Berkeley who co-authored the study, told Insider.

Marshall’s analysis suggests that the entire island of Manhattan or city of San Francisco would be the territory of a single T. rex.

He said he’d been wondering for years how unusual it really is to find a T. rex fossil: “When I hold a fossil in my hand, I always said to myself, ‘I know this is freakishly rare.’ But just how rare is it – one in a million or one in a trillion?”

Comparing the T. rex to the Komodo dragon

The T. rex was one of the largest carnivorous land animals that ever walked the Earth. (That accolade currently goes to the polar bear.) An adult Tyrannosaurus rex could weigh at least 5 tons. It stood about 12 to 13 feet tall at the hip and was about 40 to 43 feet long.

The larger predators are, the fewer of them can live in the same area, since there just isn’t enough food to sustain their massive size. This is known as Durham’s Law. So if researchers know how many calories a meat-eater needs to survive, they can calculate the number of predators per square mile.

While there’s no living predator that resembles the T. rex in size, Marshall compared the dinosaur’s energy needs to those of a Komodo dragon, the largest lizard on Earth.

Komodo Dragon
A Komodo dragon in Indonesia’s Komodo National Park.

Using that benchmark, he calculated that there could have been roughly 3,800 T. rex in an area the size of California at any given time – or just two in an area the size of Washington, DC.

There were about 20,000 adult T. rexes living at one time

Marshall’s team also needed to calculate three other variables to determine the total number of rexes that ever walked the planet: the total land area of suitable T. rex habitat, the dino’s average life span as an adult, and how long these predators existed on Earth.

T.rex illustration
A full-grown Tyrannosaurus rex weighed about 6 to 9 tons, stood about 12 to 13 feet high at the hip, and measured about 40 to 43 feet long.

By reviewing the locations of every T. rex fossil ever found, the study authors determined that the predator lived in about 888,000 square miles of North America – and nowhere else on Earth. Although the animal might have been able to survive in the area that’s now Siberia, Marshall said, he’d be surprised if any rex fossils were ever found outside the one continent.

Using that assumption about the T. rex’s geographic range, Marshall calculated that there could have been about 20,000 adult T. rexes alive at any given time in the species’ existence.

Figuring out how long the T. rex species was around was a bit easier – the oldest rex fossil ever found suggests the dinosaur walked the Earth for the last 2.5 million years of the Cretaceous Period, starting 68 million years ago. Then it went extinct after the Chicxulub space rock struck.

Finally, Marshall’s team calculated how long one generation of adult rexes lasted by looking at the average time span between when rexes became fully grown – at around age 15 – and when they died in their early 30s.

An artist’s depiction of a juvenile Tyrannosaurus rex.

That means that in the 2.5 million years these animals were on Earth, there were about 127,000 generations of them. Multiply that number by 20,000, and you wind up with 2.5 billion T. rexes.

However, Marshall pointed out that this number doesn’t include baby or juvenile T. rexes. Those were excluded from the calculations because research suggests juvenile rexes were smaller and faster than their adult counterparts, so hunted different prey.

T Rex in New York City
A Tyrannosaurus rex skeleton, named STAN, displayed by Christie’s Auction House in New York City, September 15, 2020.

Marshall’s team’s estimate suggests that the remains of just one in every 80 million adult T. rexes have been found. Currently, there are about 32 well-preserved, adult T. rex skeletons in public museums worldwide, Marshall said.

That means we’ve only dug up 0.00000125% of all the adult T. rexes that ever lived.

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