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The Jurassic Gallery Large Print Guide

The Jurassic Gallery

Peterborough under the sea


This guide covers the first floor Jurassic Gallery : Peterborough under the sea
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Peterborough under the Sea

Where you’re standing was once over 50 metres underwater.

Peterborough stands on dry land today –but the sea bed beneath our feet is packed with clues from the past. Fossils dug from the limestone and clay give us a detailed picture of life in the Jurassic.

In fact, Peterborough is one of the best places in the world to learn about this period, which saw an explosion in animal and plant populations.

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Time and Place

Warm and watery, Peterborough was a very different place 165 million years ago. A shallow sea covered the area, and the climate was much warmer than today.

So why is the local landscape so different now?

The Jurassic Period was a very long time ago. It ended 145 million years ago, after lasting 54 million years. The Jurassic is the middle period of the Mesozoic era, which covers all the time that dinosaurs were alive.

But to put things in perspective, the Jurassic is just one brief period in the Earth’s long history. The oldest fossils ever found are over 600 million years old!

Peterborough was much closer to the equator in Jurassic times. Together with warmer global temperatures, the local climate would have felt as balmy as the Bahamas.

In the 145 million years since the Jurassic Period, the continents have moved hundreds of miles. Ever since the Earth formed, the rocky plates on its surface have moved around very slowly, powered by the heat in the planet’s core.

Today, the continents continue to move as they collide and separate throughout time.

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Life on land

Sauropods, allosaurs and stegosaurus – these giant dinosaurs dominated England’s islands and uplands in Jurassic times. While Peterborough was underwater, dinosaurs lived nearby on forest-covered hills, in swampy valleys and alongside tidal marshes.

So if dinosaurs lived on dry land, why do we find them in the fossil record of Peterborough, which was underwater?

If a dinosaur happened to die near a river, some of their bones might be carried downstream to the sea which covered Peterborough during the Jurassic Period. There, they would sink to the soft, muddy seabed and could become fossils.

That’s why the ancient rock and clay of Peterborough occasionally contains fossilised remains of land-dwelling dinosaurs.

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Beneath our feet

Under Peterborough, the land has three main rock types..

Lime-rich mud covered the bottom of Peterborough’s shallow sea, 165 million years ago. Today, the mud has been compressed into limestone.

The limestone is made of tiny balls called ooliths. They formed as the sea gently rolled sandgrains around, gradually coating them in the lime-rich mud.

Bits of broken seashells and corals in the stone show that the sea was shallow and stormy, churning up the mud and the bodies of sea creatures.

Limestone has been a favoured building material since medieval times. Peterborough Cathedral and the museum building show how stonemasons could cut and carve the hardwearing limestone.

A thick layer of clay formed at the bottom of the deep sea that covered Peterborough in the Late Jurassic, 155 million years ago.

When animals died and sank to the soft clay sea floor, they were gradually covered by sediment and preserved as fossils. Now, the clay gives us a record of the sheer variety of life, from spiral-shelled ammonites to the remains of huge marine reptiles.

Today, the dark grey clay is still quarried for use in brick-making. This was a major industry in Peterborough, and many of its houses are made out of Oxford Clay bricks.

Gravel, sand and peat came much later to Peterborough, during the Ice Age 40,000 years ago.

Gravel, sand and peat came much later to Peterborough, during the Ice Age. By this time the land had moved north and risen out of the ancient sea.

The gravel today is extracted and used widely for construction and on driveways.

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Internationally important discoveries – Fossils

People have collected fossils from the area for at least 150 years. Study of local specimens, now owned by museums all around the world as well in Peterborough Museum’s own collection, has added to scientists’ understanding of the way life has evolved.

There’s often great excitement when a unique fossil comes to light for the first time. Scientists refer to it as the type specimen and use it to identify all similar fossils found later. Peterborough Museum’s fossil collection includes several type specimens.

The fossil-collecting heyday in Peterborough began over 100 years ago, when brick-making was a major local industry.

Workers quarried Jurassic clay in brick pits around the city. As they dug, they often revealed and rescued interesting fossils.

The brick quarries still yield fossil finds today, many of which are displayed in museums all over the world.

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Collectors

The brick-pits near Peterborough have attracted fossil collectors and scientists from all over the world. However, many of the best discoveries have been made by people living locally.

Alfred Leeds 1847 –1917

As boys, Alfred Leeds and his brother Charles collected fossils near their family’s farm at Eyebury, south of Peterborough. Alfred went on to run the farm, and in his spare time studied the fossils that were being discovered in the local brick-pits. He paid quarrymen to look out for good fossils for him, which he would then excavate himself.

Entirely self-taught, Alfred amassed a huge collection of fossils at the farm, where he entertained visiting professional scientists.

Leeds became an important fossil collector, and one of his greatest finds was Leedsichthys, the biggest species of fish ever known.

Alan Dawn 1923 –2010

This gallery is dedicated to Alan Dawn, a volunteer at Peterborough Museum for three decades. He was a great amateur palaeontologist, specialising in the fossils of the Peterborough area. His work has been recognised nationally. In 1990 he was the first recipient of the Palaeontological Association’s Award for Amateur Palaeontologists.

Alan made incredibly important fossil discoveries, including a nearly complete plesiosaur, and a totally new kind of pliosaur which was named after him. Nearly all the skeletons here were first prepared and assembled by Alan and his team.

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Peterborough’s unique fossils

The Jurassic sea was home to the biggest species of fish ever known.

Local fossil-hunter Alfred Leeds found remains of a bony fish and a gigantic tail in about 1886. He sent them to the Natural History Museum in London, and the palaeontologists there named the huge fish Leedsichthys problematicus –‘Leedsicthys’ meaning “Leeds’ fish”, and ‘problematicus’ as so few bones were found, it was a ‘problem’ to know what the creature looked like or how big it was.

But in 2001, a near-complete skeleton came to light in the Star Pit brick quarry near Peterborough. Finally, scientists had the bones they needed to reconstruct the fish and work out its appearance and size.

A team of fossil experts excavated the creature, over a period of 2 years. The bones were later cleaned here at the Museum.

By putting all the evidence together, scientists now think Leedsichthys could have grown to a length of over 16 metres – the largest fish ever known.

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Denizens of the deep

If you could dive into the warm Jurassic ocean, you’d find an underwater world teeming with activity and life.

As sunlight dapples the surface of the shallow sea, a huge pliosaur hunts a plesiosaur for its next meal.

A baby ichthyosaur is flexing its large tail fin for the first time after being born at sea.

Every now and then a ferocious shark or crocodile snaps up an ammonite or a slippery belemnite, while a huge-eyed Ophthalmosaur looks on.

The diversity of the big marine reptiles here - the ‘denizens of the deep’ - is remarkable. It makes Peterborough one of the best places anywhere for finding out about the evolution of life in the sea.

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Creatures in the ancient sea

Peterborough’s Jurassic sea was packed with creatures of all sizes, from microsopic to monstrous. The small fish, ammonites and belemnites feasted on shoals of plankton. They in turn became food for larger creatures. At the top of the food chain were the large ichthyosaurs, plesiosaurs and crocodiles.

Over thousands of generations,Peterborough’s marine reptiles developed special features for living at sea.

Ichthyosaurs had huge eyes for seeing their prey underwater, while the Metriorhynchus crocodile had a two-lobed tail for swimming, with flippers instead of feet.We see evidence of these features in the creatures’ fossilised remains.

Ichthyosaurs evolved to live only in the sea. Their huge eyes developed so they could see prey in the deep, dark waters. Such big eyes needed strong muscles to help them focus and to resist the water pressure. These muscles were attached to a ring of overlapping bones in each eye socket.

Steneosaurus crocodiles had a very strong but flexible back shield made of interlocking, bony scales called scutes. The shield extended all the way from the neck to the tail. As well as protecting the animal from attack, the back shield gave extra leverage to the muscles that powered swimming and hunting.

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Swimming and hunting

From the bones in their flippers to the shape of their teeth, Peterborough’s marine reptiles adapted to suit their lifestyle. The fossil record reveals how plesiosaurs evolved efficient flippers for swimming, while pliosaurs and ichthyosaurs developed different shaped teeth to catch their prey.

Plesiosaurs could swim effortlessly underwater with their four big flippers and streamlined bodies. Inside their flippers were rows of interlocking disks that had evolved from toe bones,showing they had once been land animals. These, along with a flattened limb bone, made a powerful paddle for swimming.

Fossil plesiosaur vertebrae (spine bones) always have this characteristic shape. The long-necked Cryptoclidus had more than 30 neck vertebrae like these, all held tightly together with muscles and ligaments to keep the neck straight and in line when the animal swam through the water.

Ichthyosaur vertebrae are shorter and wider than those of the long-necked plesiosaurs. Shaped like modern dolphin, ichthyosaurs were streamlined to swim rapidly through the water, sometimes diving deep to find their food.

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Life in the sea

Shrimps, snails, plankton and fish –the range of creatures in the Jurassic ocean made rich pickings for larger animals.

During the Jurassic, life changed and evolved enormously. Marine reptiles feasted on tasty invertebrates (creatures with no backbone) along with small fish and microscopic plankton.

Jurassic Fish

The shallow sea supported a huge variety of fish of all sizes and shapes, adapted for life at different depths in the water.

Near the surface, shoals of fast-swimming Caturus hunted smaller fish. The vast Leedsichthys –the biggest fish ever known –cruised harmlessly among them, gulping in water and filtering plankton to eat.

In mid-water, there were sharks. Asteracanthus used its flattened teeth to crush and eat ammonites, while Hybodus snared fish with specialised rows of sharp teeth.

Down in the depths, Lepidotes crushed shellfish between its teeth and sucked in the edible parts. The ‘moon-fish’ Dapedium munched on shrimps and shellfish, protected from predators by its thick scales.

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Spineless Wonders

Invertebrates (creatures with no backbone) thrived in the Jurassic ocean. Burrowing, squirting, floating, crawling or rippling – they could propel themselves along in lots of different ways. From the surface of the ocean to the sea floor they became the most numerous creatures in the Jurassic sea.

Belemnites had a long, soft body and ten tentacles. They escaped from predators by releasing a smoke-screen of ink.

Ammonites were soft-bodied animals with tentacles similar to a squid and a spiral shell.

Ammonites evolved and became extinct very quickly. Their fossil shells are common and distinctively patterned, making them useful for dating rocks. If you find identical ammonite species in two rock samples, you know the rocks are the same age.

Brachiopods and bivalves are two kinds of shellfish with paired shells or valves. Bivalves usually have two symmetrical shells of similar size, whilst brachiopods tend to have valves of different sizes and shapes.

Sea snails, or gastropods, had coiled shells. Around Peterborough it is unusual to find fossils of the shells themselves, which dissolved away. Only internal casts, made of the mud that filled the dead shell, are preserved.

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Extinction

Over 95% of all the animals and plants that have ever lived are now extinct.

Extinction is a natural event.

When new species arise or the environment changes, any existing species that are out-competed by the new arrivals, or cannot cope with the changed conditions, become extinct.

However, nearly all the creatures that thrived in the Jurassic died out at the end of the Cretaceous Period, about 65.5 million years ago. This mass extinction suggested something more dramatic may have been the cause.

Scientists have found evidence of high levels of Iridium in rocks which were deposited when the mass extinction occurred.

Some believe that the Iridium could be from an extra-terrestrial meteor that hit the Gulf of Mexico at this time, while some think that it came from huge volcanic eruptions going on in India.

Either of these catastrophic events could have caused devastating environmental changes.

Others believe the extinction was more gradual, caused by a combination of natural disasters and other factors including a sea-level fall and climate change.

The mass extinction that killed the dinosaurs was just one of several mass extinctions in Earth’s history. In the biggest, 250 million years ago, 96% of all marine animals and 70% of life on land died out.

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Uncovering the secrets of fossils

Fossils are full of clues about the past –if you know what to look for. When palaeontologists study an ancient animal, they look at its anatomy, how it moved, how it died, and who its relatives might be.

Pachycostasaurus dawnii – a marine reptile first uncovered in Peterborough – shows how palaeontologists used these clues to piece together what an animal was like.

Pachycostasaurus was a pliosaur with unusual characteristics. Unlike other pliosaurs, which were fierce predators, it had a small head and teeth adapted for eating small, soft prey.

The main special feature scientists found however, was that its ribs and other bones were thick and heavy. The extra weight acted as ballast, allowing Pachycostasaurus to swim slowly along the sea bed while it searched for food. Air-breathing pliosaurus were naturally buoyant; they had to work hard to swim to the bottom, but Pachycostasaurus could do it with little effort.

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