Skip to 0 minutes and 6 secondsRICHARD TWITCHETT: So my name's Richard Twitchett. I'm a researcher from the Natural History Museum. And my specialty is looking at mass extinction events in the past, and the history of the evolution of biodiversity through time. So the ecosystems that we find at the present day have a long evolutionary history. And most of the modern fauna that we see in the marine ecosystems at the present day can trace their roots back to the early Mesozoic. About 250 million years ago, there was a major mass extinction event that wiped out 95% of species on the planet.

Skip to 0 minutes and 41 secondsAnd in the aftermath and the recovery of that event, the groups that survived and radiated and evolved over the next 100 million, 150 million years really seeded the modern oceans. So this evolution of the modern faunas took place through the Triassic, the Jurassic, and the Cretaceous periods of the Mesozoic. And in the cabinets behind me, we have some of this history laid out, from the Triassic through to the Cretaceous. Now, this is a time that we talk about as being a Mesozoic marine revolution. We had the evolution of lots of different groups of organisms, especially predators, that were evolving to eat the shells of benthic animals.

Skip to 1 minute and 33 secondsPrior to the Mesozoic, there were very few shell crushing predators around, or animals that can bore into shells. So a lot of benthic animals didn't have particular defences to shell crushing. As we come through the Mesozoic, a number of different groups, especially the fish, sharks, rays, started to diversify. And this drove an arms race between the predators and the prey. And one of the big ways that animals can escape from durophagous shell-crushing predators is to adopt an infaunal lifestyle. So they became much more adept at burrowing into the sediment to escape predators.

Skip to 2 minutes and 17 secondsAnd we see this especially in the late Jurassic and the Cretaceous, with particular groups, for example, like the echinoderms-- so Echinoids that are so important in benthic ecosystems today. Burrowing Echinoids really first evolved in the Mesozoic, in the Jurassic and into the Cretaceous. And we can find their fossils in the rocks of that age, showing the development of this infaunal behaviour and function. So it's the rock and fossil record that we find preserved in the rocks of the UK, and indeed, around the world, that give us the evidence for this long evolutionary history of modern marine ecosystems. So at the present day, we can go into marine environments. We can look at shallow marine environments very easily from the beach.

Skip to 3 minutes and 9 secondsWe can go into slightly deeper environments. But even the deep seas is difficult to get to at the present day and remains largely unexplored. The rock record gives us a fossil history of lots of different environments. And because of plate tectonics and the movement of the Earth's crust, a lot of this history, preserved in the rocks as fossils, is now available for us at the surface that we can go along and collect and analyse.

Skip to 3 minutes and 41 secondsSo in many ways, it's actually easier to find out about deep ocean environments of the past, because we can go to the rocks that record this information that are here on the surface for us, than it is actually to go to the deep ocean of the present with all the difficulties that that entails. So it's this rock and fossil record that stretches back hundreds of millions of years that we can access as palaeontologists that gives us the only real data that we have on the long term evolutionary history of marine biodiversity on the planet.

History of Biodiversity

In this video, Professor Richard Twitchett from the Natural History Museum, London, explains the evolution of modern marine fauna from the Mesozoic through the Triassic, Jurassic and Cretaceous periods.

Speaking from the fossil room in the Lyme Regis Museum, Richard discusses the evolution of different feeding mechanisms and how this forced species to burrow into marine sediments to avoid predation, a process known as infaunalisation. He also highlights the importance of fossils and how they provide the key to understanding the evolution of marine species.

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This video is from the free online course:

Beneath the Blue: The Importance of Marine Sediments

University of Southampton