How Long Were Dinosaurs on Earth?

Other than the gigantic bones they left behind, dinosaurs are lost to history. Yet, they still exert a powerful hold on our imaginations. They grew larger than any other land animal in Earth’s history and dominated the planet’s landmasses for millions of years. Dinosaurs have been integral to the fields of paleontology, archeology, geology, and biology since they were first discovered. Yet, many of us still wonder how long dinosaurs were on Earth before their dramatic end.

Dinosaur Discoveries

Although there were discoveries prior to the 1820s, the recognized scientific study of non-avian dinosaurs dates back to 1824. William Buckland, a professor of geology at Oxford, became the first person to describe and name a dinosaur, Megalosaurus, in an address to the Geological Society of London. The term “dinosaur” was coined by the British paleontologist Richard Owen in 1841. The name is derived from a combination of the Greek words deinos, meaning terrible or fearfully great, and sauros, which means lizard or reptile.

Soon after the dinosaurs were discovered, scientists began piecing together their history. They devised a system in which all of dinosaur history, from their evolution to their extinction, neatly fits into the Mesozoic Era between 250 million and 66 million years ago. This is why the Mesozoic Era is sometimes called “The Age of the Dinosaurs.”

How Long Were Dinosaurs on Earth?

The Mesozoic Era is composed of three different periods: the Triassic, the Jurassic, and the Cretaceous. While all dinosaurs lived during this time, different species lived during different periods. For example, Stegosaurus, shown in the bottom right of the image above, had been extinct for around 80 million years before the first Tyrannosaurus rex was ever born. Below, we’ll discuss the history of each period, as well as the dinosaurs that lived then.

Triassic Period (252 to 201 Million Years Ago)

Dinosaurs first arose in the Middle to Late Triassic Period about 230 to 240 million years ago. At this time, the landmass of Earth was one large continent called Pangea. A massive extinction event called the Permian mass extinction occurred about 252 million years ago. It was said to have wiped out more than 90% of all life on the planet. Scientists now believe the reason for the event was massive volcanic activity in modern-day Siberia that caused catastrophic changes to the environment.

Despite everything we know about the dinosaurs, their actual evolutionary origins are still something of a mystery. Widespread changes in the ecosystem made it possible for mammal-like animals and reptiles to dominate the land. The archosaurs, a subclass of reptile that included dinosaurs and flying reptiles, also appeared during this period. Early dinosaur species appearing in the fossil record include the small, bipedal Eoraptor and the larger Herrerasaurus.

However, at the end of the Triassic, another massive extinction event took place. Researchers believed it was also most likely caused by volcanic activity. This event wiped out many of the earliest archosaurs, but some would survive to become dominant forms of life in the Jurassic Period.

Jurassic Period (201 to 145 Million Years Ago)

The Jurassic Period is most often associated with dinosaurs in popular culture. During this period, Pangaea fractured into multiple continents. The Jurassic Period was marked by cooling temperatures, increased rainfall, and the growth of different kinds of vegetation. As a result of the changing ecosystems, dinosaurs would greatly diversify in this period.

The plentiful plant life allowed for the rise of herds of herbivorous sauropods like Brachiosaurus and Diplodocus. These long-necked giants are believed to be some of the largest land animals that ever lived. Theropods, which were bipedal and primarily carnivorous, also got bigger during this period. Allosaurus and Ceratosaurus were two common predatory theropods.

Due to the rising sea levels, there are not as many animals in the fossil record for the Middle Jurassic. So the origins of armored dinosaurs like Stegosaurus are unclear, although they lived and thrived in this important period of dinosaur history. Most paleontologists believe modern birds evolved from dinosaurs. The process may have begun in the Early Jurassic, although that debate is ongoing. However, Archaeopteryx, from the Late Jurassic Period, is often thought to be the first bird.

Cretaceous Period (145 to 66 Million Years Ago)

The Cretaceous Period was the final and, in some sense, the greatest period for dinosaur dominance. By this point, the continents had broken apart into distinct landmasses. The climate had cooled slightly, and most of the planet was still covered in dense forests all the way to the poles. This led to dinosaurs evolving into many diverse forms all over the globe. Triceratops, Iguanodon, duck-billed Hadrosaurs, and the Tyrannosaurus rex are a few of the more well-known dinosaurs that lived during the Cretaceous Period.

Other groups also evolved and diversified during the Cretaceous Period. Snakes first appeared during this period, and insects, including bees, helped distribute flowering plants. Terrestrial mammals, specifically placental mammals, also evolved during the Late Cretaceous Period.

Around 66 million years ago, the dinosaur age came to a catastrophic end. About 75% of all plant and animal species, including the remaining dinosaurs, became extinct. As an asteroid slammed into the planet with the force of 180 trillion tons of TNT, it spewed an enormous amount of ash into the atmosphere, interrupting plant photosynthesis for years afterward. Whether the extinction of non-avian dinosaurs was immediate remains an open question. Regardless, the avian dinosaurs were the only lineage to survive into the Cenozoic Era, or the “Age of Mammals.” We are still in the Cenozoic Era today.