Age of the Dinosaurs

Mesozoic (251.9 to 66 million years ago)

The Mesozoic Era, also called the Age of Reptiles and the Age of Conifers, began in the wake of the Permian-Triassic extinction event, the largest mass extinction in Earth’s history, and ended with the Cretaceous-Paleogene extinction event, whose victims included the non-avian dinosaurs. The Mesozoic was a time of significant tectonic, climate, and evolutionary activity. The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would move into their current positions during the next era. The climate of the Mesozoic was varied, alternating between warming and cooling periods.

The Mesozoic is subdivided into three periods: the Triassic, Jurassic, and Cretaceous. Click below to expand and read more about those periods.

The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events.



The Triassic began in the wake of the Permian-Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period.

The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south.

The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic-Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic.

The Triassic is separated into Early, Middle, and Late Triassic Epochs, and the corresponding rocks are referred to as Lower, Middle, or Upper Triassic. The faunal stages from the youngest to oldest are:



Dinosaurs lived in the Triassic period:

• Chindesaurus • Coelophysis • Coloradisaurus • Eoraptor • Guibasaurus • Herrerasaurus • Liliensternus • Lycorhinus • Melanorosaurus • Mussaurus • Plateosaurus • Procompsognathus • Riojasaurus • Saltopus • Staurikosaurus • Thecodontosaurus

The Jurassic constitutes the middle period of the Mesozoic Era and is named after the Jura Mountains, where limestone strata from the period were first identified.



The start of the Jurassic was marked by the major Triassic-Jurassic extinction event, associated with the eruption of the Central Atlantic Magmatic Province. The beginning of the Toarcian stage started around 183 million years ago, and is marked by an extinction event associated with widespread oceanic anoxia, ocean acidification, and elevated the temperatures likely caused by the eruption of the Karoo-Ferrar large igneous provinces. The end of the Jurassic however has no clear boundary with the following Cretaceous and is the only boundary between geological periods to remain formally undefined.

By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north, and Gondwana to the south. The climate of the Jurassic was warmer than the present, and there were no ice caps. Forests grew close to the poles, with large expanses of desert within the lower latitudes of the continents.

On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and pseudosuchian archosaurs, to one dominated by dinosaurs alone. The first birds appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards and the evolution of therian mammals. Crocodilians made the transition from a terrestrial life to an aquatic mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates.

The Jurassic is separated into Early, Middle, and Late Jurassic Epochs, and the corresponding rocks are referred to as Lower, Middle, or Upper Jurassic. The ages of the Jurassic from the youngest to oldest are:

Dinosaurs lived in the Early Jurassic period:

• Aardonyx • Ammosaurus • Anchisaurus • Barapasaurus • Cryolophosaurus • Dilophosaurus • Heterodontosaurus • Jingshanosaurus • Kotasaurus • Lesothosaurus • Lophostropheus • Lufengosaurus • Massospondylus • Pantydraco • Sarcosaurus • Scelidosaurus • Scutellosaurus • Vulcanodon • Yimenosaurus • Yunnanosaurus

Dinosaurs lived in the Middle Jurassic period:

• Amygdalodon • Bellusaurus • Brachytrachelopan • Cetiosauriscus • Cetiosaurus • Datousaurus • Emausaurus • Eustreptospondylus • Gasosaurus • Huayangosaurus • Lapparentosaurus • Megalosaurus • Monolophosaurus • Nqwebasaurus • Omeisaurus • Patagosaurus • Podokesaurus • Poekilopleuron • Proceratosaurus • Rhoetosaurus • Segisaurus • Shunosaurus • Sinraptor • Yandusaurus • Yinlong • Yuanmousaurus

Dinosaurs lived in the Late Jurassic period:

• Agilisaurus • Allosaurus • Apatosaurus • Archaeopteryx • Barosaurus • Brachiosaurus • Camarosaurus • Camptosaurus • Ceratosaurus • Chaoyangsaurus • Chinshakiangosaurus • Chirostenotes • Chungkingosaurus • Coelurus • Compsognathus • Dacentrurus • Dicraeosaurus • Diplodocus • Dryosaurus • Dubreuillosaurus • Elaphrosaurus • Euhelopus • Europasaurus • Gargoyleosaurus • Giraffatitan • Guanlong • Haplocanthosaurus • Hesperosaurus • Janenschia • Juravenator • Othnielia • Piatnitzkysaurus • Saurophaganax • Stegosaurus • Torvosaurus • Tuojiangosaurus • Yangchuanosaurus • Yingshanosaurus

The Cretaceous is the third and final period of the Mesozoic era, as well as the longest. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period.



The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites, and rudists, while dinosaurs continued to dominate on land. The world was ice free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous-Paleogene extinction event, a large mass extinction in which many groups, including nonavian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the abrupt Cretaceous-Paleogene boundary, a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic eras.

The Cretaceous is separated into Early and Late Jurassic Epochs, and the corresponding rocks are referred to as Lower or Upper Jurassic. The ages of the Cretaceous from the youngest to oldest are:

Dinosaurs lived in the Early Cretaceous period:

• Acrocanthosaurus • Afrovenator • Amargasaurus • Aragosaurus • Archaeoceratops • Atlascopcosaurus • Austrosaurus • Baryonyx • Becklespinax • Beipiaosaurus • Caudipteryx • Cedarpelta • Chubutisaurus • Confuciusornis • Deinonychus • Eotyrannus • Equijubus • Erketu • Fukuiraptor • Fukuisaurus • Gastonia • Giganotosaurus • Gobisaurus • Harpymimus • Hylaeosaurus • Hypsilophodon • Iguanodon • Irritator • Jinzhousaurus • Jobaria • Laeallynasaura • Liaceratops • Ligabuesaurus • Lurdusaurus • Malawisaurus • Microraptor • Minmi • Muttaburrasaurus • Neovenator • Nigersaurus • Probactrosaurus • Protoarchaeopteryx • Psittacosaurus • Rebbachisaurus • Sauropelta • Shamosaurus • Shanag • Silvisaurus • Sinocalliopteryx • Sinornithosaurus • Sinosauropteryx • Sinovenator • Stenopelix • Suchomimus • Supersaurus • Tenontosaurus • Utahraptor • Valdosaurus • Zephyrosaurus

Dinosaurs lived in the Late Cretaceous period:

• Abelisaurus • Achelousaurus • Achillobator • Aegyptosaurus • Alamosaurus • Albertaceratops • Albertosaurus • Alectrosaurus • Alioramus • Alvarezsaurus • Ampelosaurus • Anchiceratops • Ankylosaurus • Anserimimus • Antarctosaurus • Aralosaurus • Archaeornithomimus • Argentinosaurus • Arrhinoceratops • Auchasaurus • Avaceratops • Avimimus • Bacrosaurus • Bagaceratops • Bamiraptor • Borogovia • Brachylophosaurus • Buitreraptor • Carcharodontosaurus • Carnotaurus • Centrosaurus • Chasmosaurus • Citipati • Conchoraptor • Corythosaurus • Daspletosaurus • Deinocheirus • Deltadromeus • Dromaeosaurus • Dromiceiomimus • Dryptosaurus • Edmontonia • Edmontosaurus • Einiosaurus • Eolambia • Erlikosaurus • Euoplocephalus • Gallimimus • Garudimimus • Gasparinisaura • Gilmoreosaurus • Gorgosaurus • Goyocephale • Graciliceratops • Gryposaurus • Hadrosaurus • Heyuannia • Homalocephale • Hypacrosaurus • Indosuchus • Isisaurus • Jaxartosaurus • Khaan • Kritosaurus • Lambeosaurus • Leptoceratops • Lophorhothon • Magyarosaurus • Maiasaura • Majungasaurus • Mapusaurus • Masiakasaurus • Maxakalisaurus • Microceratus • Micropachycephalosaurus • Mononykus • Nanshiungosaurus • Nedoceratops • Nemegtosaurus • Neuquenosaurus • Nipponosaurus • Noasaurus • Nomingia • Nothronychus • Opisthocoelicaudia • Ornithomimus • Orodromeus • Oryctodromeus • Oviraptor • Pachycephalosaurus • Pachyrhinosaurus • Panoplosaurus • Paralititan • Parasaurolophus • Parkosaurus • Pentaceratops • Pinacosaurus • Prenocephale • Prosaurolophus • Protoceratops • Protohadros • Quaesitosaurus • Rhabdodon • Rinchenia • Rugops • Saichania • Saltasaurus • Saurolophus • Saurornithoides • Secernosaurus • Segnosaurus • Shantungosaurus • Shuvuuia • Sonidosaurus • Spinosaurus • Stegoceras • Struthiomimus • Struthiosaurus • Styracosaurus • Talarurus • Tanius • Tarbosaurus • Tarchia • Telmatosaurus • Therizinosaurus • Thescelosaurus • Torosaurus • Triceratops • Troodon • Tsagantegia • Tsintaosaurus • Tylocephale • Tyrannosaurus • Udanoceratops • Unenlagia • Urbacodon • Velociraptor • Zalmoxes • Zuniceratops