What Are Dinosaurs?

Dinosaurs were a group of reptiles that existed on Earth from about 250 million years ago to 65 million years ago.

While we often imagine dinosaurs as big, lumbering lizards, they had a wide variety of forms and sizes in ancient times. There were not only giant dinosaurs, but also small ones that could run quickly.

It’s thought that some small dinosaurs even evolved to fly and became the ancestors of birds.

Bipedal and Quadrupedal

Dinosaurs are classified into two main groups based on how they walked: bipedal (walking on two legs) and quadrupedal (walking on four legs).

The bipedal group, known as theropods, includes famous dinosaurs like Tyrannosaurus and Velociraptor.

Tyrannosaurus

The quadrupedal group, known as ornithischians, includes dinosaurs like Triceratops and Brachiosaurus.

Triceratops

Differences from Reptiles

Dinosaurs evolved from a common ancestor shared with modern reptiles like turtles, crocodiles, and lizards. However, dinosaurs had a distinct advantage: they had two legs that extended straight down from their hips, which allowed them to move quickly.

Two legs extending straight down from their hips, allowing them to move quickly.

It is also believed that some dinosaurs had feathers and were warm-blooded. Unlike cold-blooded reptiles that rely on sunlight to warm their bodies, these dinosaurs were endothermic, meaning they could warm their own bodies internally.

Considered to be endothermic (warm-blooded) creatures

Relationship with Birds

Relationship with Birds

Modern birds are considered to be the direct descendants of dinosaurs.

Birds are considered to be the survivors of dinosaurs.

Birds and dinosaurs are closely related in terms of evolution, and some features seen in birds today are shared with their ancient dinosaur ancestors.

Extinction of Dinosaurs

Dinosaurs were wiped out by a massive extinction event that occurred about 65 million years ago. This event, known as the Cretaceous–Paleogene extinction event, is believed to have been caused by the impact of a giant asteroid.

The “Asteroid Impact Theory” is said to have driven the dinosaurs to extinction.

This event caused the disappearance of most dinosaurs from Earth and had a huge impact on subsequent biological evolution.

Discovery and Research

Dinosaur fossils have been discovered all over the world and are studied by paleontologists.

Dinosaur fossils are being discovered all over the world.

This research has provided a great deal of information about dinosaur ecology and evolution.