The Age of Dinosaurs

The Great Dying

The Permian period ended in the most severe extinction event in Earth's history. Vast volcanic eruptions in Siberia poured out lava and greenhouse gases, warming the planet and acidifying the oceans. As much as 90% of marine species and most life on land was wiped out.

Why it matters: The 'Great Dying' emptied the world's ecosystems and cleared the way for new groups of animals to rise — among the survivors were the ancestors of the dinosaurs.

Ichthyosaurs Return to the Sea

As life recovered from the Great Dying, some reptiles returned to the water. Ichthyosaurs — sleek, dolphin-shaped 'sea dragons' — became fast marine predators; smaller ichthyosaurs survived until around 90 million years ago.

Why it matters: Among the first large reptiles to fully adapt to ocean life, ichthyosaurs even gave birth to live young at sea. Their fossils were among those that first led scientists to accept that species could go extinct.

The First Dinosaurs

The oldest definitive dinosaurs appear in ~230-million-year-old rocks of the Ischigualasto Formation in Argentina — small, bipedal forms such as Eoraptor and the early carnivore Herrerasaurus. They were still rare members of ecosystems dominated by other archosaurs.

Why it matters: These first dinosaurs were already recognisably dinosaurs, implying their lineage had been evolving even earlier. From this modest beginning came the dominant land animals of the next 165 million years.

The First Mammals

Tiny, shrew-like mammals and their close relatives appeared alongside the earliest dinosaurs. Brasilodon quadrangularis, from what is now Brazil, shows mammal-like features around 225 million years ago, with Morganucodon following by about 205 million years ago.

Why it matters: Mammals — our own lineage — did not arise after the dinosaurs but at the same time, living for over 150 million years as small, mostly nocturnal creatures in a dinosaur-dominated world.

The First Pterosaurs Take Flight

The first pterosaurs appear in the fossil record around 215 million years ago. These flying reptiles were not dinosaurs but close archosaur cousins — and they were the first vertebrates ever to evolve powered flight, tens of millions of years before birds.

Why it matters: Pterosaurs would rule the skies for the rest of the age of dinosaurs and eventually produced the largest flying animals that have ever lived.

The End-Triassic Extinction

A mass extinction around 201 million years ago — one of the 'big five' — wiped out up to 80% of species. It was probably driven by enormous volcanism (the Central Atlantic Magmatic Province) as the supercontinent Pangaea began to rift apart, and it killed off many of the archosaurs that had competed with dinosaurs.

Why it matters: With their rivals gone, dinosaurs inherited a nearly empty world. They diversified explosively in the Jurassic and became the dominant land animals for the next ~135 million years.

Pangaea Breaks Apart

During the Jurassic, the supercontinent Pangaea broke apart, opening new seaways and separating the land into drifting continents. The climate grew warmer and wetter, and lush vegetation spread across the world.

Why it matters: The breakup created varied new habitats and isolated dinosaur populations, driving them to evolve into an extraordinary range of forms — including the largest animals ever to walk the Earth.

Plesiosaurs Rule the Seas

Long-necked plesiosaurs became dominant ocean predators through the Jurassic and Cretaceous. Fully adapted to open water, they swam using four large wing-like flippers.

Why it matters: Together with the ichthyosaurs, plesiosaurs ruled the Mesozoic seas for tens of millions of years. Centuries later, their fossils would help inspire the legend of the Loch Ness Monster.

Diplodocus and the Giant Sauropods

In the Late Jurassic, long-necked sauropods reached enormous sizes. Diplodocus, one of the longest dinosaurs ever known, roamed the Morrison Formation of western North America alongside other giant plant-eaters.

Why it matters: Sauropods were the largest animals ever to live on land. Their immensely long necks let them browse vegetation far out of reach of any other herbivore.

Stegosaurus, the Plated Dinosaur

Stegosaurus, a large Late Jurassic plant-eater of the Morrison ecosystem, carried two rows of tall bony plates along its back and a spiked tail for defence.

Why it matters: Its distinctive plates — probably used for display and to help control body temperature — make Stegosaurus one of the most instantly recognisable of all dinosaurs.

Allosaurus, Apex Predator of the Jurassic

Allosaurus was the top predator of Late Jurassic North America — a powerful bipedal carnivore with a large skull and blade-like teeth. It hunted the same landscapes as Stegosaurus and the giant sauropods.

Why it matters: Known from abundant fossils, Allosaurus reveals the Jurassic food web at its peak — tens of millions of years before Tyrannosaurus rex evolved.

Archaeopteryx and the Origin of Birds

Archaeopteryx, a small feathered dinosaur from Late Jurassic Germany, had wings, feathers and a wishbone like a bird, yet also sharp teeth, clawed hands and a long bony tail like other dinosaurs. The first specimen was found in 1861 — just two years after Darwin's On the Origin of Species.

Why it matters: It became the iconic 'missing link' showing that birds evolved from dinosaurs, and powerful early evidence for evolution.

How we know: Discovered in the Solnhofen limestone of Bavaria in 1861, Archaeopteryx arrived at the perfect moment to support Darwin's new theory. Scientists now recognise even older bird-like dinosaurs.

The First Flowers Bloom

Flowering plants (angiosperms) appeared and rapidly spread during the Cretaceous, diversifying across the world and transforming ecosystems on land.

Why it matters: Flowers reshaped life on Earth — co-evolving with insects and offering new foods for dinosaurs. Nearly all the plants and crops we rely on today descend from this Cretaceous revolution.

Feathered Dinosaurs Revealed

Exceptionally preserved Cretaceous fossils show that many dinosaurs — especially small meat-eaters — were covered in feathers. The finds confirmed that feathers first evolved in dinosaurs long before any animal could fly.

Why it matters: They cemented the link between dinosaurs and birds and overturned the old picture of dinosaurs as purely scaly reptiles.

Patagotitan and the Largest Dinosaurs

Titanosaurs — the last and largest of the sauropods — reached staggering sizes in the Cretaceous. Patagotitan, from ~101-million-year-old rocks of Argentina, measured about 37.5 metres long and weighed an estimated 57 tonnes.

Why it matters: These giants were among the largest land animals ever to exist — longer than a blue whale and as heavy as around ten elephants — testing the physical limits of life on land.

Spinosaurus, the River Predator

Spinosaurus, a huge sail-backed predator from Cretaceous North Africa, was even longer than Tyrannosaurus rex. A remarkably complete skeleton found in Morocco in 2014 revealed dense bones, paddle-like feet and a fin-shaped tail, suggesting it hunted fish in rivers.

Why it matters: It may be the most water-adapted large dinosaur known — but exactly how aquatic Spinosaurus really was remains hotly debated among palaeontologists.

How we know: The 2014 Moroccan skeleton, and the later discovery of its tail, led some scientists to propose Spinosaurus was a swimming, fish-hunting predator; others argue it was a semi-aquatic wader. The debate is unresolved.

Mosasaurs, the Last Sea Monsters

As the ichthyosaurs faded, giant marine lizards called mosasaurs rose to rule the Late Cretaceous oceans. Powerful swimmers related to today's monitor lizards and snakes, they were the top predators of the seas.

Why it matters: Mosasaurs dominated the oceans for the final tens of millions of years of the Mesozoic and then vanished in the same mass extinction that ended the dinosaurs.

Velociraptor, the Feathered Hunter

Velociraptor, a Late Cretaceous predator from Mongolia, was in reality about the size of a turkey — far smaller than in the movies — and covered in feathers, with a large sickle-shaped claw on each foot.

Why it matters: Its feathers and bird-like body underscore how closely related the raptors were to birds, blurring the old line between dinosaur and bird.

Triceratops and the Horned Dinosaurs

Triceratops appeared around 68 million years ago, in the final stretch of the age of dinosaurs. This massive plant-eater bore three facial horns and a large bony frill, and shared its world with Tyrannosaurus rex.

Why it matters: Its horns and frill — used for defence and display — make Triceratops an icon of the Late Cretaceous, and it was among the dinosaurs still thriving when the asteroid struck.

Tyrannosaurus rex, the Tyrant King

Tyrannosaurus rex, one of the largest land predators of all time, lived in the final couple of million years of the dinosaur age in western North America. It reached around 12 metres long, had up to 60 teeth as long as 20 centimetres, and a bite several times more powerful than a lion's. The first skeleton was found in 1900 by Barnum Brown.

Why it matters: The apex predator of its ecosystem and among the very last non-bird dinosaurs, T. rex has become the most famous dinosaur of all.

The Deccan Traps Erupt

Around the end of the Cretaceous, one of the largest volcanic events in Earth's history — the Deccan Traps, in what is now India — poured out immense floods of lava over hundreds of thousands of years, releasing climate-altering gases across the boundary.

Why it matters: Scientists still debate whether this volcanism, the Chicxulub asteroid impact, or the two together drove the mass extinction — but the eruptions almost certainly stressed global ecosystems.

How we know: The Deccan eruptions spanned the extinction boundary. Researchers disagree on their exact role: some models make the asteroid the decisive killer, others give volcanism a leading part.

The Day the Mesozoic Died: The Chicxulub Impact

A city-sized asteroid slammed into what is now the Yucatán Peninsula of Mexico, carving out the vast Chicxulub crater. The impact triggered wildfires, tsunamis and a global 'impact winter' as debris blotted out the Sun. Around three-quarters of all species — including every non-bird dinosaur — died out.

Why it matters: This mass extinction ended the 165-million-year age of dinosaurs and reset the course of life on Earth.

How we know: In 1980 the physicist Luis Alvarez and colleagues found a worldwide layer of iridium — rare on Earth but common in asteroids — at the boundary, and proposed an impact; the matching Chicxulub crater was later identified beneath Mexico.

Birds: The Dinosaurs That Survived

One group of small, feathered theropod dinosaurs lived through the mass extinction: the birds. Every bird alive today — from sparrows to ostriches — is a living dinosaur, descended from Cretaceous ancestors.

Why it matters: Dinosaurs never truly went extinct. Their lineage continues in the thousands of species of birds all around us today.

After the Dinosaurs: The Age of Mammals

With the non-bird dinosaurs gone, mammals — until then mostly small and nocturnal — rapidly diversified to fill the empty ecosystems, growing larger and taking on new roles through the Cenozoic Era.

Why it matters: The extinction that ended the dinosaurs opened the way for the age of mammals — and, ultimately, for primates and human beings.