Picture a world with no ice caps, sea levels over 140 metres higher than today, and a single supercontinent slowly tearing itself apart.

Welcome to the Jurassic Period — the chapter of Earth's history when dinosaurs stopped being background characters and took over the entire planet.

A Period Born From Catastrophe

The Jurassic began in the aftermath of one of the five greatest mass extinction events in Earth's history. Up to 80% of all species were wiped out at the end of the preceding Triassic Period — likely due to massive volcanic eruptions releasing enormous quantities of sulphur dioxide and carbon dioxide into the atmosphere, destabilising the global climate.

Dinosaurs survived. And in the ecological vacuum that followed, they flourished. "Whether it's chance or whether there's some competitive advantage that they had is a matter of debate," says Dr Susie Maidment, dinosaur researcher at the Natural History Museum. "But what happened in the aftermath is that the dinosaurs really radiated and then became the dominant terrestrial organisms."

Small Beginnings

Early Jurassic dinosaurs were nothing like the giants we picture today. Among the first were the heterodontosaurids — small, bipedal reptiles reaching no more than two metres in length. What made them unusual was their teeth: unlike most dinosaurs, which have uniform teeth along their jaws, heterodontosaurids carried multiple tooth types, including chewing teeth and prominent canine-like fangs.

"It's been suggested that these were possibly omnivorous, but they might have been herbivorous," Susie explains. Their exact place on the dinosaur family tree remains debated.

By the end of the Jurassic, the transformation was extraordinary. Dinosaurs had diversified from a handful of small, similar-looking reptiles into an enormous range of forms — including four-legged giants with elaborate body structures like Stegosaurus, Brachiosaurus, and Diplodocus. Every land animal over a metre long was a dinosaur.

The Middle Jurassic Gap

Here lies one of palaeontology's most frustrating puzzles. The Middle Jurassic is among the worst-documented periods in dinosaur history. Rising sea levels during this epoch submerged much of the land where fossils of terrestrial animals would otherwise be found — particularly across North America and Europe, where most dinosaur research has traditionally been focused.

"Across the places on Earth where we've looked for dinosaurs and other terrestrial vertebrates — North America and Europe, primarily — we actually have marine rocks deposited over this time," Susie explains. Without a solid fossil record, the origins of entire dinosaur groups — including stegosaurs, armoured dinosaurs, and iguanodontians — remain poorly understood.

One of the few places offering a window into this lost world is Morocco's Atlas Mountains, where Susie and her colleagues have been uncovering remarkable finds — including the oldest known ankylosaur, Spicomellus afer, and one of the earliest stegosaurs, Adratiklit boulahfa. "Everything we're finding is basically new," she says.

Jurassic Britain: Underwater and Teeming With Life

For much of the Early and Middle Jurassic, southern England was submerged beneath a shallow sea. The 150-kilometre Jurassic Coast — including Lyme Regis, where pioneering fossil hunter Mary Anning made her celebrated discoveries — preserves extraordinary marine fossils from this time, including ichthyosaurs and plesiosaurs.

Inland, on what were once shallow island landscapes in modern-day Oxfordshire and Gloucestershire, dinosaur remains tell a richer story. Further north, the Isle of Skye and parts of Yorkshire preserve dinosaur footprints from beaches and tidal flats of the Middle Jurassic.

A World Ruled by Gymnosperms

While dinosaurs dominated the land, the plant world belonged to the gymnosperms — conifers, cycads, and ginkgos. Flowering plants had not yet established themselves. The tropics were surprisingly dry, and most plant life thrived at mid-latitudes instead.

The Late Jurassic fossil forest preserved in southern England's Portland Stone offers a vivid snapshot: short, scrubby conifers around 12 to 15 metres tall, standing in a salty lagoon landscape not unlike the modern Mediterranean. Scientists believe the forest was flooded and preserved by earthquakes triggered by the rifting of the supercontinent Pangea as the Atlantic Ocean began to open.

How the Jurassic Ended — and Why It's Complicated

The Jurassic's end was less dramatic than its beginning. Rather than a sudden global catastrophe, the fossil record points to a gradual faunal turnover — particularly pronounced in North America, where a major mountain-building event may have eliminated key dinosaur habitats. In Europe, Jurassic fauna appear to have persisted somewhat longer.

"There's this really big faunal turnover and what caused that isn't totally clear," Susie admits. As the Jurassic gave way to the Cretaceous, iguanodontians and ankylosaurs were already rising to dominance — setting the stage for the final, spectacular chapter of the dinosaur age.

The Jurassic lasted 56 million years — longer than the entire span since the asteroid that ended the dinosaurs. It's a reminder that what we call a "golden age" in hindsight was, for the creatures living through it, simply the slow, relentless work of survival, adaptation, and time. Makes our own era feel rather brief, doesn't it?