Dinosaurs: Facts about the reptiles that roamed Earth more than 66 million years ago

March 14, 2025

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Quick facts about dinosaurs

Where they lived: Dinosaur fossils have been found on every continent, including Antarctica.

What they ate: Some ate plants, while others ate animals, including other dinosaurs.

How big they were: The smallest dinosaurs were the same size as hummingbirds at only 2 inches (5 centimeters) long, while the longest reached over 120 feet (37 meters) in length.

Dinosaurs are the extinct relatives of birds that roamed the lands and seas of ancient Earth. They first appeared around 240 million to 230 million years ago in the Triassic Period, and went extinct around 66 million years ago, at the end of the Cretaceous Period, when a massive asteroid slammed into Earth.

During the Triassic Period, when dinosaurs first evolved, all the continents we know today were clumped together in a single landmass called Pangaea. Over tens of millions of years, Pangaea split apart, eventually coming to resemble the map of the world we know today. Dinosaur fossils have been found on every continent around the globe, including Antarctica.

Some of the most famous types of dinosaurs include Tyrannosaurus rex, Triceratops, Stegosaurus and Velociraptor, many of which were featured in the popular “Jurassic Park” movies. Most of these dinosaurs lived tens of millions of years apart from each other.

Dinosaurs belong to a group of animals known as archosaurs, which also includes modern-day animals such as birds and crocodiles.

5 fast facts about dinosaurs

The heaviest known dinosaur is thought to be Argentinosaurus, a supermassive titanosaur that lived during the Cretaceous period. It may have weighed up to 180,800 pounds (82,000 kilograms).
An asteroid wiped out the dinosaurs. The crash left a giant crater around 110 miles (180 kilometers) wide off Mexico’s coast.
The word “dinosaur” means “terrible lizard” in Latin, and it was first made up in 1842 by paleontologist Richard Owen.
Birds are actually dinosaurs. They evolved from theropods, a group of mostly meat-eaters that included Velociraptor and T. rex.
Pterodactyls are flying reptiles that lived at the same time as the dinosaurs, but they are not actually dinosaurs.

Everything you need to know about dinosuars

Did dinosaurs have feathers?

Dinosaurs were once thought to look like modern lizards, covered in green scales. However, some dinosaur species were actually covered in feathers, just like birds today.

We know this because some fossils from creatures such as Archaeopteryx and Sinosauropteryx — both theropod dinosaurs — have preserved feather imprints. And some Velociraptor fossils have tiny bumps on their arm bones where feathers were attached, just like in modern birds.

At first, paleontologists thought only theropod dinosaurs had feathers. However, scientists have found traces of downy feathers on fossils of a plant-eating dinosaur, suggesting that feathers may have been more common in dinosaurs than we thought.

Some dinosaurs may have used feathers to stay warm, court mates or even fly. For instance, paleontologists think a tiny chicken-size dinosaur named Microraptor had feathers on all four limbs to help it glide or even fly.

Feathers may have been very colorful in some species. Fossils of Sinosauropteryx even had preserved pigment structures named melanosomes, which allowed scientists to figure out it had an orange and white striped tail. These bright colors could have been used for mating displays, or intimidation of others, just like how modern birds use their colorful feathers today.

A model of a dinosaur with feathers

Paleontologists believe that some dinosaur species had feathers. (Image credit: brandstaetter images via Getty Images)

Why were dinosaurs so big?

Many species of dinosaurs were enormous. The largest group of all the dinosaurs were the titanosaurs, which included Argentinosaurus and Patagotitan.

Patagotitan is one contender for the longest dinosaur discovered so far, measuring 37.5 meters 123 feet (37.5 m) long, weighing (62 tons) 57 metric tons, and standing 8 meters (26 feet) tall. Argentinosaurus may have been heavier though; it reached lengths of 115 feet (35 m) and weights of up to 110 tons (100 metric tons). Some other dinosaurs, such as Supersaurus and Giraffatitan, may have grown even longer or taller than these species.

It’s not clear why some dinosaurs were so big, though scientists think that their upright posture, wide hips, light bones and unique foot structure may have made it easier to grow so large.

Dinosaurs also probably had very efficient breathing thanks to air sacs within their light bones. These sacs helped them take up oxygen during both inhalation and exhalation. This may have contributed to their growth to such gigantic sizes.

And the long necks of titanosaurs allowed them to graze on food right on the tops of trees where no others could reach, meaning they could consume lots of food without moving much and burning much energy.

How did the dinosaurs go extinct?

Most dinosaurs suddenly went extinct about 66 million years ago after an asteroid struck Earth. You can see evidence of this impact at the Chicxulub crater on the Yucatán Peninsula in Mexico, which measures about 110 miles (180 km) across.

The asteroid was likely between 6.2 and 9.3 miles (10 and 15 km) wide, and its collision with Earth triggered intense wildfires, tsunamis, and massive earthquakes around the world. The impact also threw huge amounts of dust and debris into the atmosphere, blocking sunlight for years. With less sunlight, temperatures dropped, plants died, and food chains collapsed. Additionally, sulfur in the atmosphere from the asteroid impact then fell as acid rain, killing off tiny plants that drift in the ocean known as plankton, which many animals relied on for food. These effects wiped out 75% of animals on Earth in a short period of time.

While a lot of volcanoes were also erupting around the same time, most scientists think the asteroid caused the mass extinction.

Only small theropod dinosaurs survived the extinction; the ancestors of modern-day birds. Our small mammal ancestors probably survived extinction because they could burrow and eat a wide range of foods.

An illustration of a T. rex watching an asteroid hit earth.

Most dinosaurs went extinct after an asteroid hit Earth. (Image credit: MARK GARLICK/SCIENCE PHOTO LIBRARY via Getty Images)

Do dinosaurs still exist?

Dinosaurs still exist today — as birds. Modern birds evolved from the small, feathered theropod dinosaurs that survived the mass extinction event 66 million years ago.

Unlike giant dinosaurs, most early birds were small, which meant they required less food to survive. After the asteroid impact, food became scarce, but smaller birds could survive on seeds and insects. And unlike ground-dwelling dinosaurs, birds could fly to new areas to find food and shelter, giving them a huge survival advantage when ecosystems collapsed.

With all the larger non-avian dinosaurs dead, the earliest birds rapidly evolved, and today there are about 11,000 bird species. Modern birds share many traits with dinosaurs, including hollow bones and wishbones.

Early birds were also better able to survive the cold conditions after the asteroid strike than many reptiles. This is because like mammals, birds are also warm-blooded, meaning they can regulate their body temperature during extreme climate changes.

Some animals around today are not considered dinosaurs, but stayed quite similar since the age of the dinosaur. Both crocodiles and dinosaurs belong to a group called archosaurs and share a common ancestor that lived around 250 million years ago. However, crocodiles have changed very little in the last 200 million years or so, making them one of the closest things we have to prehistoric reptiles.