When Did the Dinosaurs Live?

Updated February 21, 2017 | Factmonster Staff

Dinosaurs lived throughout the Mesozoic Era, which began 245 million years ago and lasted for 180 million years. It is sometimes called the Age of the Reptiles. The era is divided into three periods.


245 to 208 million years ago

  • During the Triassic period, all land on Earth existed as one enormous mass. It was called Pangaea. The supercontinent slowly began to break up during the Triassic Period.
  • Some reptiles, frogs, turtles and crocodiles existed earlier, but dinosaurs didn’t appear until late in the Triassic period.
  • The period marked the rise of small, lightly built dinosaurs.
  • The first mammals evolved during the Triassic period.
  • Most of the plants that existed were evergreens.
  • The period ended with a mass extinction that wiped out most animals and reptiles. An entire order of plants or animals dies out in a mass extinction. The dinosaurs that survived flourished in the next period, the Jurassic.

Dinosaurs that lived during the Triassic period include:

Coelophysis (“hollow form”; found in the U.S.): a 9-foot long carnivore that was quick on its feet

Desmatosuchus (“link crocodile”; found in Texas): a reptile that looked like a crocodile and had sharp spikes on its back

Eoraptor (“dawn thief”; found in Argentina): the earliest-known dinosaur; walked on two feet

Ichthyosaurs (“fish lizards”; found in England, Germany, Greenland and Canada): this order of marine reptiles dominated the ocean during the Triassic period

Iguanadon (“iguana teeth”; found in North America, Europe and Asia): the first dinosaur to be discovered; its bones and teeth are different from any other known reptile

Plateosaurus (“flat lizard”; found in dozens of sites in Europe): an herbivore that had five-fingered hands with a clawed thumb

Proganochelys (found in Germany and Thailand): the earliest-known turtle


208 to 146 million years ago

  • The supercontinent continued to break apart
  • Dinosaurs ruled the land and flourished during the period
  • Herbivores and carnivores increased in size; some of the largest dinosaurs emerged during the Jurassic period
  • Birdlike dinosaurs first appeared
  • Flowering plants began to appear late in the period
  • The Jurassic period also ended with an extinction, but it was not as extensive as the one in the Triassic period. Only a few types of dinosaurs died out.

Dinosaurs that lived during the Juraissic period include:

Allosaurus (“different lizard”; found in western North America): the biggest meat-eater of the period, measuring about 40 feet long

Apatosaurus formerly called Brontosaurus (“deceptive lizard”; found in the western U.S.): the dinosaur measured between 70 and 90 feet, but its head was only about 2 feet long

Archaeopteryx (“ancient wing”; found in Germany): one of the earliest-known birds, this creature shared many characteristics with dinosaurs

Compsognathus (“pretty jaw”; found in Germany, France and Portugal): the smallest-known dinosaur was about the same size as a chicken

Diplodocus (“double-beamed”; found in western North America): At 90 feet long, this was one of the longest land animals

Mamenchisaurus (“Mamenchin lizard”; found in China): this dinosaur’s neck measured an amazing 46 feet long

Stegosaurus (“plated lizard”; found in U.S., Europe, India, China and Africa): a three-ton giant with the brain the size of a walnut


146 to 65 million years ago

  • Pangaea continued to separate into smaller continents
  • A wide variety of dinosaurs roamed the land
  • Birds flourished and spread all over the globe
  • Flowering plants developed
  • Mammals flourished
  • Dinosaurs became extinct by the end of the period. The extinction, the second largest of all time, marked the end of the Age of Reptiles and the beginning of the Age of Mammals.

Dinosaurs that lived during the Cretaceous period include:

Ankylosaurus (“bent/crooked lizard”; found it Montana and Alberta, Canada): the most heavily armed dinosaur, with bony plates, studs and spikes lining its entire back

Giganotosaurus carolinii: (“giant southern lizard”; found in Argentina): measuring about 45 feet long and weighing about 8 tons, it holds the record as the largest carnivore

Hadrosaurus (“bulky lizard”; found in New Jersey): this herbivore had a toothless bill but many cheek teeth

Megaraptor (“huge robber”; found in Argentina): a fast runner with a sickle-shaped claw on each foot

Orinthomimus (“bird mimic”; found in China): at an estimated 40 to 50 miles per hour, this was the fastest dinosaur

Seismosaurus (“seismic lizard”; found in New Mexico): considered the largest dinosaur, it measured 120 feet long and stood about 18 feet high

Triceratops (“three-horned face”; found in Canada and western U.S.): this quadraped (four-footed) dinosaur walked on its four stumpy legs and used the three horns on its head for protection.

Troodon (“wounding tooth”; found in North America and Asia): largest brain-to-body ration of all known dinosaurs; believed to be as intelligent as modern birds

Tyrannosaurus rex (“tyrant lizard”; found in North America and Asia): T. rex, king of the dinosaurs, dominated the period.

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