14 recent discoveries that have changed the way we think about dinosaurs

T. rexes preferred a leisurely pace most of the time, strolling around at about 3 mph, according to a study published in 2021.

Scientists built a 3D computer model to understand the ideal "resonance" of the T. rex bodies.

Every animal has an ideal resonance, meaning the walking speed at which they can move their body forward most comfortably while spending the least energy.

"Many animals have a roughly similar preferred walking speeds," between 2.2 and 3.1 mph, Pasha van Bijlert, an author on the study, told Insider at the time.

If the study calculation are correct, T. rex would have been no exception.

"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 at the time.

That doesn't mean the dinosaurs could not outrun a human: scientists think they could speed up their walk, hitting peak speeds of about 25 mph, Insider previously reported.

That's much faster than the average human's running speed.

But any strut above 12 mph and the tons-heavy predators would risk shattering their bones, a 2017 study found.

Because birds and crocodiles lay hard-shelled eggs, paleontologists had assumed their ancestors did too.

But a 2020 analysis of egg fossils found in the Gobi desert upended that theory.

It revealed the eggs, from a 75-million-year-old, sheep-sized herbivore called Protoceratops, were likely soft-shelled, like those of turtles, lizards, and snakes.

That may why it has been difficult to find eggs from some species of dinosaurs.

"We have all these other animals, but we don't have any eggs. It's bizarre," Mark Norell, lead author of the study, told Insider at the time. "My guess is they were all laying soft-shelled eggs."

As many as 2.5 billion T. rexes may have lived in total, a 2021 study estimated.

The study looked at the average size of a T. rexes' territory — about 40 miles — how much they would have eaten, and the other resources they needed over the 2.5 million years they existed.

The scientists estimated that as many as 20,000 adult T. rexes were alive at any one time.

According to a 2021 study, fossils of 100 eggs and 80 skeletons were found at one site in Patagonia, suggesting these dinosaurs, of the Mussaurus patagonicus species, may have lived in a herd.

The eggs were clustered by groups of 8 or 30, close enough to suggest this may have been a breeding ground.

Remains of juveniles and adults were also found at the site.

"I went to this site aiming to find at least one nice dinosaur skeleton. We ended up with 80 skeletons and more than 100 eggs (some with embryos preserved inside!)" Diego Pol, a researcher with the Egidio Feruglio paleontology museum in Patagonia and the lead author of the new study, told Insider via email.

According to a 2019 exhibit at the American Museum of Natural History, called "T. rex: The Ultimate Predator," hatchlings were surprisingly vulnerable.

They had a 60% chance of dying within their first year of life, and were only the size of a turkey. They had an incredible growth spurt, gaining up to 1,700 pounds per year until they reached full adult size at age 20.

A 2022 study described the skeleton of a new species of carcadontosaurs called Meraxes gigas. Like a T. rex, it had an enormous head and was very big: about 36 ft long.

And like the T. rex, it had tiny little arms.

The surprise was that this animal died 20 million years before the T. rex. So the tiny arms evolved independently.

Paleontologists have known since the late 2000s that another branch of the dinosaur family, the abelisaurs, were also "armless."

"This is a real repeated pattern among giant carnivores: They are shrinking the arms down," said Dave Hone, a paleontologist from Queen Mary University in London who was not involved in the paper, speaking to Insider at the time.

"Once is a novelty. Twice is: huh! Third time? Okay, this is happening again and again," said Hone.

That three huge carnivorous with tiny heads could have evolved independently to have tiny little arms probably means they had an evolutionary purpose.

Scientists have put forward many ideas for their use.

Some have suggested that the arms were used to help grasp a mate during sex, or to counterbalance their massive heads during attacks.

Others said that perhaps the arms helped the predator rise from a fall, or to topple triceratopses over during hunting (this is called the "cow-tipping" hypothesis).

Hone is doubtful about any of them.

"I'm all in favor of the possibility of a mechanical function in these reduced arms. But I want a reason that stands up to even 10 seconds of thought and scrutiny and I've yet to see one," he said at the time.

The site, nicknamed "Tanis" after the last resting place of the Ark of the Covenant in the 1981 film "Raiders of the Lost Ark," was highlighted in a 2022 BBC documentary that showed its fossils of incredible quality.

Tanis, in North Dakota, has yielded some amazing fossils.

These include triceratops skin, pictured above, and a Thescelosaurus leg, seen in a video here.

Tiny glass-like particles of molten rock were found lodged in the gills of fish fossils found at the site. The scientists that study the site have said these were kicked up in the sky following the impact of the 7.5 mile-wide meteorite that hit the earth 66 million years ago, wiping out the dinosaurs.

Kate Wong, science editor of Scientific American, said in a 2019 tweet that the findings from the site "have met with a good deal of skepticism from the paleontology community."

According to a 2019 New Yorker article about the site, the owner of the fossils had an inremarkable academic career until the discovery of the site.

Robert DePalma, a relative of cinematographer Brian de Palma, insisted on contractual clauses that give him oversight over the specimens.

He has submitted very few academic papers about his findings, limiting the scrutiny other scientists can give to the findings.

Results of a dig in southernmost Chile, published in 2021 revealed a new type of dinosaur with a tail "unlike any dinosaur."

The 6.5-ft-long dinosaur, named Stegouros, had a tail "resembling an Aztec war club, with seven pairs of blades lining the tail."

It would have supposedly used the tail to fight off predators.

A 2016 study using cutting-edge technology was able to recreate the actual color of this dinosaur, called Psittacosaurus, meaning "parrot lizard."

This was the third time scientists were able to figure out the color of a dinosaur from melanosomes, bits of cells that make the component that color the skin, like melanin in humans.

Using this technology, scientists think this 120 million-year-old dinosaur, which has a parrot beak and was about 5 ft. long with a bushy tail, was mainly brown with a slightly lighter underbelly, per Reuters.