Prehistoric fish
The Devonian period, around 420-359 million years ago, is often called the Age of Fishes. It marked a time of major evolutionary advances for life in both the sea and on land. This came to an end as key parts of the marine ecosystem, such as coral reefs, were devastated, and slowly died off over millions of years. Known as the Late Devonian ‘mass extinction’, it had a huge impact on life on land and in the sea, and led to over 70 percent of species on Earth becoming extinct.
One group of animals that disappeared entirely at this time were the armoured fish. These ancient sea creatures heads were covered with bony plates. Some were large predators, while others scavenged on the sea floor.
Bothriolepis were a smaller type of armoured fish. About 30cm long, they scavenged for food on the bottom of seas and lakes.
Permian monsters
Many millions of years later, at the end of the Permian period (299-252 million years ago) there was another mass extinction, when huge numbers of species went extinct at a similar time. Called the Great Dying, the causes of this mass extinction are not fully understood.
Scientists think that massive volcanic eruptions released huge amounts of sulphur dioxide and carbon dioxide into the atmosphere, leading to the loss of 90% percent of all species living around at that time. This happened slowly, over hundreds of thousands of years.
Scutosaurus, a large, armoured reptile that lived in what is now Russia, was among the many species that disappeared. It grew up to 2.5 metres long and weighed around one tonne. Despite its name, it was not a dinosaur and lived millions of years before most dinosaurs appeared.
Another predator from the Permian period was Dimetrodon. Although also often mistaken for a dinosaur, it was more closely related to mammals. About the length of a car, it had a large sail-like structure along its back and was a dominant carnivore of its time.
Dunkleosteus were enormous fish with an armour-plated neck and were at the top of the food chain. They had an incredibly powerful bite, which allowed them to crush armoured prey.
The end of the dinosaurs
Perhaps the most famous mass extinction of all took place around 66 million years ago, at the end of the Cretaceous period (145-66 million years ago). A massive asteroid struck the Yucatán Peninsula, triggering global darkness, climate disruption and bringing the age of the dinosaurs to an end. With sunlight blocked, plants could no longer photosynthesise, and ecosystems collapsed.
Dinosaurs were not the only victims, but their size and dominance make this loss especially striking. Tyrannosaurus rex, one of the most well-known dinosaurs, could not survive once the other dinosaurs it preyed on disappeared.
While many dinosaurs vanished, some smaller ones survived: the birds. Their small size, ability to fly and flexible diets may have helped them find food in a harsh environment. Over time, these survivors evolved into the birds we know today.
Quetzalcoatlus, one of the largest flying animals ever known, was also lost. It was a pterosaur rather than a dinosaur and likely fed on small vertebrates. Like all other pterosaurs, it became extinct 66 million years ago, when rapid environmental changes disrupted ecosystems around the world.
Our impact
Many experts believe we are living through another mass extinction, driven by human activity. The loss of life and the rate of extinction is happening quickly, much faster than the mass extinctions that took place millions of years ago. Unlike earlier events, this one is heavily linked to how humans use land, water and energy.
Human impacts on the natural world date back thousands of years.
The woolly mammoth is one of the best studied prehistoric animals, thanks to frozen remains found in Siberia and Alaska. Bones, tusks and teeth were also found in the UK and beyond. These large mammals stood about three metres tall and lived in cold, icy environments that helped preserve their bodies when they died. Scientists believe they disappeared due to a combination of climate warming and human hunting, and the last woolly mammoths went extinct about 4,000 years ago.
The cave bear is another species lost in the Ice Age. It was a huge, stocky animal that was mostly herbivorous. Their reasons for the cave bear’s extinction are multifaceted, comprising of a changing climate, but also competing with humans and neanderthals for habitat and shelter in caves. There is also evidence that cave bears were hunted by humans and neanderthals, perhaps contributing to their eventual demise.
The dodo, a flightless bird from Mauritius, became extinct within a century of being recorded by humans. First described by Dutch sailors in 1598, it was last sighted in 1662.
While it is often said that humans hunted the dodo to extinction, the reality is more complex. Introduced animals such as rats, cats and dogs also likely preyed on adults, eggs and chicks, and widespread deforestation destroyed their habitat.
What we could lose today
The African savannah elephant is currently listed as Endangered, mainly due to poaching and habitat loss. Its population has declined by about 70 percent over the past 40 years. Despite international bans, demand for ivory remains high, and organised crime continues to drive large scale poaching.
Encouragingly, there are increasing efforts to protect wildlife in the wake of continuing endangerment.
In the UK, birds of prey have sometimes been killed as pests by game keepers and land owners. Now, thanks to concerted conservation efforts, many species are making a comeback. Red Kites were near extinct in the UK in the 1800s, surviving in small pockets in Wales. Starting in the 1980s, conservation and breeding programmes have gradually bred and monitored them, releasing Red Kites back into the wild, which have now grown in number to thousands of breeding pairs. This effort continues today, with similar successes seen with other bird species such ospreys and golden eagles.
Directly introducing wildlife is important, but protecting their habitats is also vital to their long-term survival. Successful conservation efforts to manage and protect marshes, rivers and ponds also help protect British wildlife.
These wetlands were eroded over time, drained for farming and polluted by sewage and fertilisers. Many organisations and volunteers have been working hard to restore wetlands and habitat across the UK with positive results, like with rare water voles that have been returned to restored areas, including rivers in London.