Dinosaur Timelines
Earth’s history is divided into chunks of time and the dinosaurs ruled for about 185 million years, the timeline shows the various eras, ages or aeons. Click on a button and you will be taken to description of the main evolution of that period.
Below shows the ages placed into their four main eons.
PRECAMBRIAN: 4600-570 Million Years Ago
In the Precambrian period the single celled organisms like algae and bacteria first appeared. The Precambrian era also included the Proterozoic eon and the Archean eon. By the end of the Archean eon soft bodied animals began to appear such as worms and jellyfish.
CAMBRIAN PERIOD: 570-505 Million Years Ago
The Cambrian period saw life in the seas begin with a very large and diverse variety of life but as yet life had not evolved on land. The highest forms of life existing at this time were the trilobites, (pictured right) which reached lengths up to two feet. Green and red algae started to appear along with sponges, gastropods, and segmented worms.
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ORDOVICIAN PERIOD: 505-438 Million Years Ago
During the early Ordovician period the occurrence of widespread graptolite, conodont, and trilobite species appeared. At this point the beginnings of vertebrate fish have been found.
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SILURIAN PERIOD: 438-408 Million Years Ago
The Silurian period sees the first macro fossils of extensive terrestrial biota, in the form of moss forests along lakes and streams. Some evidence suggests the presence of predatory trigonotarbid arachnoids and myriapods in Late Silurian facies. Predatory invertebrates would indicate that simple food webs were in place that included non-predatory prey animals.
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DEVONIAN PERIOD: 408-362 Million Years Ago
Sea levels in the Devonian were generally high. Marine faunas continued to be dominated by bryozoa, diverse and abundant brachiopods, the enigmatic hederelloids, and corals. Lily-like crinoids were abundant, and trilobites were still fairly common. Among vertebrates, jaw-less armoured fish (ostracoderms) declined in diversity, while the jawed fish (gnathostomes) simultaneously increased in both in sea and fresh water. Armoured placoderms were numerous during the lower stages of the Devonian Period and became extinct in the Late Devonian, perhaps because of competition for food against the other fish species. Early cartilaginous (Chondrichthyes) and bony fishes (Osteichthyes) also become diverse and played a large role within the Devonian seas. The first abundant genus of shark, Cladoselache, appeared in the oceans during the Devonian period. The great diversity of fish around at the time, have led to the Devonian being given the name "The Age of Fish" in popular culture.
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CARBONIFEROUS PERIOD: 362-290 Million Years Ago
FISH:
Many fish inhabited the Carboniferous seas; predominantly Elasmobranchs (sharks and their relatives). These included some, like Psammodus, with crushing pavement-like teeth adapted for grinding the shells of brachiopods, crustaceans, and other marine organisms. Other sharks had piercing teeth, such as the Symmoriida; some, the petalodonts, had peculiar cycloid cutting teeth. Most of the sharks were marine, but the Xenacanthida invaded fresh waters of the coal swamps.
Terrestrial Invertebrates
Fossil remains of air-breathing insects and arachnids are known from the late Carboniferous, but so far not from the early Carboniferous. Their diversity when they do appear, however, shows that these arthropods were both well developed and numerous. Their large size can be attributed to the moistness of the environment (mostly swampy fern forests) and the fact that the oxygen concentration in the Earth's atmosphere in the Carboniferous was much higher than today. (The oxygen concentration in the Earth's atmosphere during the Carboniferous was 35% whereas the oxygen concentration in earth's current atmosphere is 21%.) This required less effort for respiration and allowed arthropods to grow larger with the up to 2.6 metres long millipede-like Arthropleura being the largest known land invertebrate of all time. Among the insect groups are the huge predatory Protodonata (griffin flies), 
among which was Meganeura, a giant dragonfly-like insect and with a wingspan of ca. 75 cm — the largest flying insect ever to roam the planet. Further groups are the Syntonopterodea (relatives of present-day mayflies), the abundant and often large sap-sucking Palaeodictyopteroidea, the diverse herbivorous "Protorthoptera", and numerous basal Dictyoptera (ancestors of cockroaches). Many insects have been obtained from the coalfields of Saarbrücken and Commentry, and from the hollow trunks of fossil trees in Nova Scotia. Some British coalfields have yielded good specimens: Archaeoptitus, from the Derbyshire coalfield, had a spread of wing extending to more than 35 cm; some specimens (Brodia) still exhibit traces of brilliant wing colors. In the Nova Scotian tree trunks land snails (Archaeozonites, Dendropupa) have been found.
Tetrapods
Carboniferous amphibians were diverse and common by the middle of the period, more so than they are today; some were as long as 6 meters, and those fully terrestrial as adults had scaly skin.[16] They included a number of basal tetrapod groups classified in early books under the Labyrinthodontia. These had long bodies, a head covered with bony plates and generally weak or undeveloped limbs. The largest were over 2 meters long. They were accompanied by an assemblage of smaller amphibians included under the Lepospondyli, often only about 15 cm long. Some Carboniferous amphibians were aquatic and lived in rivers (Loxomma, Eogyrinus, Proterogyrinus); others may have been semi-aquatic (Ophiderpeton, Amphibamus, Hyloplesion) or terrestrial (Dendrerpeton, Tuditanus, Anthracosaurus).
One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. These included the earliest sauropsid reptiles (Hylonomus), and the earliest known synapsid (Archaeothyris). These small lizard-like animals quickly gave rise to many descendants. The amniote egg allowed these ancestors of all later birds, mammals, and reptiles to reproduce on land by preventing the desiccation, or drying-out, of the embryo inside. By the end of the Carboniferous period, the amniotes had already diversified into a number of groups, including protorothyridids, captorhinids, aeroscelids, and several families of pelycosaurs.
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PERMIAN PERIOD: 290-248 Million Years Ago
The climate in the Permian period was quite varied. At the start of the Permian, the Earth was still at the grip of an Ice Age from the Carboniferous. Glaciers receded around the mid-Permian 
period as the climate gradually warmed.
During the Permian, all the Earth's major land masses were collected into a single supercontinent known as Pangaea. A new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmasses create climates with extreme variations of heat and cold ("continental climate") and monsoon conditions with highly seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea. Such dry conditions favoured gymnosperms, plants with seeds enclosed in a protective cover, over plants such as ferns that disperse spores. The first modern trees (conifers, ginkgos and cycads) appeared in the Permian.
Early Permian terrestrial faunas were dominated by pelycosaurs and amphibians, the middle Permian by primitive therapsids, and the late Permian by more advanced therapsids such as gorgonopsians and dicynodonts. Towards the very end of the Permian the first archosaurs appeared, a group that would give rise to the dinosaurs in the following period. Also appearing at the end of the Permian were the first cynodonts, which would go on to evolve into mammals during the Triassic. There were no aerial vertebrates.
A group of small reptiles, the diapsids started to abound. These were the ancestors to most modern reptiles and the ruling dinosaurs as well as pterosaurs and crocodiles.
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TRIASSIC PERIOD: 248-208 Million Years Ago
During the Triassic, both marine and continental life show an adaptive radiation beginning from the starkly impoverished biosphere that followed the Permian-Triassic extinction. Corals of the hexacorallia group made their first appearance. The first flying vertebrates, the pterosaurs, evolved during the Triassic.
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JURASSIC PERIOD: 208-144 Million Years Ago
During the Jurassic period on land, large archosaurian reptiles remained dominant. The Jurassic was a golden age for the large herbivorous dinosaurs known as the sauropods—Camarasaurus, Apatosaurus, Diplodocus, Brachiosaurus, and many others—that roamed the land late in the period. They would have fed on either the prairies of ferns, palm-like cycads and bennettitales, or the higher coniferous growth, according to their adaptations. They were preyed upon by large theropods as for example Ceratosaurus, Megalosaurus, Torvosaurus and Allosaurus. During the Late Jurassic, the first birds, like Archaeopteryx, evolved from small Coelurosaurian dinosaurs. Ornithischian dinosaurs were less predominant than saurischian dinosaurs, although some like stegosaurs and small ornithopods played important roles as small and medium-to-large (but not sauropod-sized) herbivores. In the air, pterosaurs 
were common; they ruled the skies, filling many ecological roles now taken by birds. Within the undergrowth were various types of early mammals, as well as tritylodont mammal-like reptiles, lizard-like sphenodonts, and early lissamphibians.
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CRETACEOUS PERIOD: 144-65 Million Years Ago
During the Cretaceous, the late Paleozoic – early Mesozoic supercontinent of Pangaea completed its tectonic breakup into present day continents. The climate showed a cooling trend that had been seen in the last epoch of the Jurassic. There is evidence that snowfalls were common in the higher latitudes and the tropics became wetter than during the Triassic and Jurassic.
On land, mammals were a small and still relatively minor component of the fauna. Early marsupial mammals evolved in the Early Cretaceous, with true placentals emerging in the Late Cretaceous period. The fauna was dominated by archosaurian reptiles, especially dinosaurs, which were at their most diverse stage. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded they faced growing competition from the adaptive radiation of birds, and by the end of the period only two highly specialized families remained. During the Cretaceous, insects began to diversify, and the oldest known ants, termites and some lepidopterans, akin to butterflies and moths, appeared. Aphids, grasshoppers, and gall wasps appeared.
In the seas, rays, modern sharks became common. Marine reptiles included ichthyosaurs in the early and middle of the Cretaceous, becoming extinct during the late Cretaceous, plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous.
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TERTIARY PERIOD: 65-2 Million Years Ago
The Cenozoic era, the Tertiary period is divided into five epochs: Paleocene, Eocene, Oligocene, Miocene, and Pliocene.
At the beginning of the period, mammals replaced reptiles as the dominant vertebrates. Each epoch of the Tertiary was marked by striking developments in mammalian life. The earliest recognizable hominoid relatives of humans such as Proconsul. Modern types of birds, reptiles, amphibians, fish, and invertebrates were either already numerous at the beginning of the period or appeared early in its history. Modern families of flowering plants evolved. Marine invertebrates and non-mammal marine vertebrates experienced only modest evolution.
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QUATERNARY: PERIOD 2-0 Million Years Ago
The Quaternary, the second and last of the Cenozoic period is divided into two epochs: Pleistocene and Holocene. Mammoths, Cattle, deer, and of course, Homo habilis, Homo erectus, and Homo sapiens.
During this time, substantial glaciers advanced and retreated over much of North America and Europe, parts of South America and Asia, and all of Antarctica. The Great Lakes formed and giant mammals flourished in parts of North America and Eurasia not covered in ice. These mammals became extinct when the last Ice Age ended about 11,700 years ago. During the Quaternary period, mammals, flowering plants, and insects dominated the land.