The age of giant sauropods
Jurassic
Mesozoic Era · 201.4 – 145 million years ago
The Jurassic Period lasted from 201.4 to 145 million years ago, the middle chapter of the Mesozoic Era. Over these 56 million years dinosaurs became the dominant land animals, reaching sizes never matched before or since, while the supercontinent Pangaea began to break apart.
It was the world of long-necked giants like Brachiosaurus, plated Stegosaurus and the predator Allosaurus, of ichthyosaurs and plesiosaurs in the seas, and of Archaeopteryx, one of the earliest known birds. The opening of the Atlantic Ocean also began here, setting the map on its path towards the one we know today.
Key facts
- Began
- 201.4 MaMillion years ago
- Ended
- 145 MaMillion years ago
- Duration
- 56.4 million years
- Era
- Mesozoic“Middle life”
- Global temperature
- ~23°CRoughly 22–24°C · today 14.5°C
- Plants on land
- Forests
- Atmospheric CO₂
- ~1,000–2,000 ppm (≈ 4–7× pre-industrial); uncertain
- Oxygen
- Roughly similar to or slightly below today's 21%; debated
- Sea level
- Rising; shallow seas flooded much of Europe
- Continents
- Pangaea splitting into Laurasia and Gondwana
- Signature life
- Sauropods, Stegosaurus, Allosaurus, ammonites, Archaeopteryx
- Began with
- Dinosaurs taking over after the end-Triassic extinction
- Ended with
- No mass extinction; a gradual turnover into the Cretaceous
Ages follow the International Chronostratigraphic Chart (ICS). Global temperatures are rough reconstructions after Scotese et al. (2021); ancient CO₂, oxygen and sea-level values carry large uncertainties.
Epochs of the Jurassic
- Early Jurassic201.4 Ma – 174.7 Ma
- Middle Jurassic174.7 Ma – 161.5 Ma
- Late Jurassic161.5 Ma – 145 Ma
Continents and oceans
At the start of the Jurassic, Pangaea was still one landmass, but it was already splitting along the rift valleys formed in the Late Triassic. As North America pulled away from Africa, the central Atlantic Ocean opened, with true ocean floor forming by the Middle Jurassic, and the Gulf of Mexico began to open too.
By the end of the period, Pangaea had effectively divided into a northern continent, Laurasia, and a southern one, Gondwana, which itself was starting to rift between Africa and the combined landmass of Antarctica, India and Australia. The vast Panthalassic Ocean, ancestor of the Pacific, still covered much of the globe, and the Tethys Ocean separated Laurasia from Gondwana in the east.
Rising seas spread across the continents, drowning much of Europe beneath warm, shallow water dotted with islands. These seas laid down the limestones and clays that now form much of southern England, France and Germany.
Climate and atmosphere
The Jurassic was a greenhouse world, warmer than today, with no large permanent ice sheets, although some evidence suggests cooler intervals at times. Forests grew at high latitudes, and as Pangaea broke up and seaways opened, the interior deserts of the Triassic gave way to more humid climates in many regions.
Carbon dioxide was considerably higher than today, though estimates vary widely. Around 183 million years ago, volcanic eruptions in southern Africa and Antarctica (the Karoo–Ferrar province) are linked to the Toarcian Oceanic Anoxic Event, a spell of warming and oxygen-starved seas that caused a notable marine extinction.
Life in the Jurassic
With many of their Triassic competitors gone, dinosaurs diversified into a huge range of forms. Mammals remained small but were surprisingly varied, and the oceans teemed with reptiles, fish and shelled cephalopods.
On land
Sauropods such as Brachiosaurus, Diplodocus and Apatosaurus grew to well over 20 metres long, the largest animals ever to walk the Earth up to that time. They shared Late Jurassic landscapes with Stegosaurus and with predators such as Allosaurus and Ceratosaurus. Small mammals, including the swimming, beaver-like Castorocauda, lived in their shadow.
In the air
Pterosaurs ruled the skies, from long-tailed forms like Rhamphorhynchus to the first short-tailed pterodactyloids. Meanwhile small feathered dinosaurs such as Anchiornis lived in what is now China, and around 150 million years ago Archaeopteryx, one of the earliest known birds, flew over the lagoons of southern Germany.
In the seas
Ichthyosaurs, long-necked plesiosaurs and big-headed pliosaurs such as Liopleurodon hunted in Jurassic seas. Ammonites and squid-like belemnites were abundant, and their fossils are so widespread that geologists use ammonites to divide Jurassic time into fine slices.
Plants
Forests were dominated by conifers, including relatives of today's monkey puzzles and redwoods, along with cycads, ginkgos, tree ferns and horsetails. There were no grasses, and flowering plants had not yet clearly appeared.
Timeline of key events
- 201.4 Ma
Jurassic begins
Dinosaurs rise to dominance after the end-Triassic extinction removes many rivals.
- 183 Ma
Toarcian Oceanic Anoxic Event
Volcanism-driven warming starves parts of the oceans of oxygen and causes a marine extinction.
- 175 Ma
Central Atlantic seafloor spreading
By roughly this time, new ocean floor is forming between North America and Africa.
- 160 Ma
Feathered dinosaurs in China
Small feathered dinosaurs such as Anchiornis live in forests and lakes of what is now north-eastern China.
- 155 Ma
Morrison giants roam
Brachiosaurus, Diplodocus, Stegosaurus and Allosaurus share the floodplains of western North America.
- 150 Ma
Archaeopteryx takes flight
One of the earliest known birds lives on islands in a warm lagoon in what is now Bavaria.
- 145 Ma
Cretaceous begins
The Jurassic ends quietly, with no mass extinction at the boundary.
How the Jurassic ended
Unlike the periods before and after it, the Jurassic did not end with a mass extinction. The transition into the Cretaceous 145 million years ago saw some turnover, with certain groups of sauropods, stegosaurs and marine animals declining, but nothing like a global catastrophe.
Because no single dramatic event marks the boundary, it has long been one of the hardest to pin down, and the international time scale still lists its age as approximate.
Where to see Jurassic fossils
The Morrison Formation of the western United States, visible at Dinosaur National Monument on the Colorado–Utah border, has produced Brachiosaurus, Diplodocus, Stegosaurus and Allosaurus. The Solnhofen limestone of Bavaria, Germany, is world-famous for Archaeopteryx and finely preserved pterosaurs, fish and insects.
Britain's Jurassic Coast in Dorset and East Devon, a UNESCO World Heritage Site, is where Mary Anning collected ichthyosaurs and plesiosaurs, and its beaches still yield ammonites today. Rich Jurassic sites are also found in China, including the feathered dinosaurs of Liaoning and the giant sauropods of Sichuan.
Surprising facts about the Jurassic
- Stegosaurus and Tyrannosaurus rex never met: they are separated by roughly 80 million years, more time than separates T. rex from us.
- Many of the stars of the Jurassic Park films, including Tyrannosaurus and Velociraptor, actually lived in the later Cretaceous Period.
- The fine-grained Solnhofen limestone, which preserves Archaeopteryx, was quarried for lithographic printing plates, and quarrying is how its fossils came to light.
- Mary Anning, working on the Dorset coast in the early 1800s, found some of the first ichthyosaur and plesiosaur skeletons ever recognised by science, despite having little formal education.
- Liopleurodon is often portrayed as a 25-metre monster, but most scientists estimate it reached roughly 6–7 metres, still a formidable predator.
- The Jurassic takes its name from the Jura Mountains on the border of France and Switzerland, where limestones of this age are widespread.
Where it sits in deep time
The globe beside this article shows Earth 170 million years ago, reconstructed from the PALEOMAP paleo-elevation models. Step to another period and watch the continents drift into place.