In Search of the ‘Real’ Jurassic…
If you pick up a copy of the current Dorset Magazine, you will see that our very own Programme Manager, Sam Scriven has shared thrilling tales of Dorset dinosaurs and reveals what this coastline looked like millions of years ago with the help of paleoartist Dr Mark Witton.
Stretching 95 miles along the Dorset and East Devon coast, the Jurassic Coast World Heritage Site is an iconic landscape enjoyed by hundreds of thousands of people each year. However, many are unaware of the fascinating heritage that lies hidden in its rocks, cliffs and beaches. Taking a bone or shell of a creature that once called this place home – I want you to leap back in time with me to long-vanished deserts, seas and swamps of the Jurassic Coast. Our fossils provide access to the landscapes of the Mesozoic Era – the age of reptiles. Spanning 186 million years of Earth History, the Mesozoic is made up of the Triassic, Jurassic and Cretaceous periods, each hosting wonderful examples of evolution.
The Great Dying
Before the dinosaurs came the Great Dying – the greatest mass extinction event ever known. The reasons for this momentous event are complex, but not as interesting as what happened afterwards. The Great Dying happened at the boundary between the Permian and Triassic Periods, around 252 million years ago. Some 95% of marine species and 70% of land species were wiped out. Such a huge loss of biodiversity radically altered the make-up of Earth’s ecosystems, opening up opportunities for those creatures that survived.
Incredibly rare Triassic fossils from the sandstone cliffs of East Devon offer a glimpse of those survivors. Fragments of bone and teeth point to a group of reptiles known as rauisuchians.
These extinct creatures, related to crocodiles, could grow to several metres long. Some had magnificent sails on their backs and collectively they may have occupied the top of the foodchain in the post-extinction deserts of Triassic Devon. In certain layers, munched and broken fragments of prey animals lie strewn amongst the splayed, five-toed footprints the rauisucians left behind. The
fossilised remnants of a reptile buffet lunch. However, other more agile three-toed reptiles were appearing to compete with them. These began a legacy that would last for 170 million years –dinosaurs.
A Realm of Marine Reptiles
By the end of the Triassic period dinosaurs and other giant reptiles dominated land, sea and air. The early Jurassic rocks around Lyme Regis are a treasure trove of fossils that reveal life in the
marine realms of this reptile empire. Giant marine reptiles such as ichthyosaurs have had their ecological role re-filled by dolphins and other cetaceans. Plesiosaurs on the other hand
have no modern counterpart. Palaeontologists are still baffled by their defining feature, a long, graceful neck. Did they use it to ambush prey in murky water, or for sweeping their needle-tooth jaws through shoals of fish? The fact that plesiosaurs were first discovered over 150 years ago and scientists still haven’t cracked it shows how even familiar fossils can stubbornly withhold secrets
about their enigmatic past.
Diversify and thrive
The thrilling spectacle of huge dinosaurs, marine reptiles and pterosaurs (flying reptiles) should not distract us from another important event taking place during the Jurassic and Cretaceous periods – the diversification of mammals. By the end of the Jurassic period mammals had evolved to become a successful part of Mesozoic ecosystems and were fairly widespread. True, they tended to be fairly small and superficially resembled rodents, but size isn’t necessarily a sign of failure to thrive. Many are thought to have preyed on dinosaur eggs and young dinosaurs.
In 2017 the tiny fossilised teeth of two new mammal species were recovered from the earliest Cretaceous rocks of the Jurassic Coast. The surprising thing was that these teeth belonged to
a group directly related to all modern mammals, including human beings. Their names are Durlstotherium newmani and Durlstodon ensomi, recognising the place of their discovery
– Durlston Bay – and two individuals who have contributed much to the study of Purbeck’s geology and fossils, Paul Ensom and Charlie Newman.
The Extinction of the Dinosaurs
Death starts and finishes the extraordinary geological story of the Jurassic Coast. Beginning 252 million years ago with the Great Dying, we finish with the extinction of the dinosaurs around 66
million years ago. This event would likely have been visible in our strata, as a thin layer of sediment rich in the rare element iridium. Sadly, the rocks of that precise age were eroded away in our part of the world. The concentration of iridium, abundant in asteroids, is considered to be evidence of a major meteorite impact and subsequent environmental catastrophe. Around 75% of
species, including dinosaurs, pterosaurs, giant marine reptiles and ammonites did not survive. But let’s not be too maudlin. Without the ecological opportunity created by the Great Dying there would not have been the dinosaurs and their relatives. Without their ultimate demise mammals might never have realised their own potential for dazzling diversity. As homo sapiens we can explore this incredible shared history. Evolution has armed us with powerful brains capable of imaginative speculation and contemplation. All we need from this unique World Heritage Site is a handful of rocks and fossils and their promise of a journey into the sublime.