The skeleton of a 23ft plesiosaur, one of prehistoric Earth's most fearsome marine reptiles, is now on display at the Natural History Museum in London. Kate Whittington, the museum's exhibition and interpretation manager, explains how its long neck allowed its head to get a head start on its body, enabling it to sneak up on prey before its body and flippers created a disturbance in the water.
Jurassic Oceans: Monsters of the Deep
The bones of this immense predator are among the centrepieces of Jurassic Oceans: Monsters of the Deep, an immersive exhibition showcasing fossils, casts, and 3D-printed sculptures of marine creatures that ruled the oceans while dinosaurs roamed the land more than 66 million years ago. The exhibition also features ancient crocodile-like creatures and colossal squid tentacles.
The Jurassic World
Marc Jones, the exhibition's curator, explains that during the Jurassic era, the sun was slightly dimmer, about 2% less powerful, but the planet was much warmer and more humid due to higher CO2 levels. There were no permanent ice caps, so sea levels were higher, and nearly all land was joined together in the supercontinent Pangaea, surrounded by a single global ocean known as Panthalassa. Because that ocean was so vast and slow moving, circulation was limited in many places.
Ammonites and Squid
Particularly well suited to these conditions were ammonites, soft-bodied, shell-dwelling creatures related to modern cephalopods such as octopus, squid, and nautilus. Jones notes that there is evidence that squids are doing really well because the oceans are getting warmer, as their relatives did well in warmer, more stagnant oceans.
Predators of the Past
The exhibition shows how dramatically marine ecosystems have changed over time. In today's oceans, sharks are among the dominant hunters, but 200 million years ago they were middle predators, very effective hunters but also preyed upon by marine reptiles. Larger animals lurk deeper in the exhibition, including ichthyosaurs, a family of vicious long-snouted marine reptiles. Ichthyosaurs probably have the largest eye of any vertebrate animal, indicating they were speedy predators that relied on vision.
Convergent Evolution
A bottlenose dolphin skeleton is on show to demonstrate how similar their body shapes and hunting tactics are to ichthyosaurs. This is an example of convergent evolution, where two species independently evolve similar anatomy. Animals that live in similar environments and have evolved to eat similar prey tend to develop the same adaptations to achieve the same goal, but completely separately.
Extinction and Climate Change
Unlike other marine reptiles, ichthyosaurs are thought to have become extinct much earlier due to the diminishing availability of prey related to natural changes in the climate. Ammonites were a kind of high energy snack for them, and as the climate changed and ammonites started to die out, the ichthyosaurs could not adapt fast enough. The same climate story is depleting marine life today. Ocean warming, acidification, and deoxygenation threaten phytoplankton, the base of a food chain that feeds bigger species.
The T-Rex of the Sea
The grand finale of the exhibition centres on the skull of a mosasaur, known as the "T rex of the sea." These large predators ruled the oceans in the Cretaceous period, which ended about 66 million years ago. They have big pointy teeth on the outside and also teeth in the roof of their mouth to help them grip prey. When dinosaurs were living on the land, amazing things lived in the oceans, like giant marine reptiles, that we do not really have equivalents of today. We do have saltwater crocodiles and big turtles, but the role of predator is dominated by mammals.
A Stark Warning
For Jones, looking back offers a stark warning. There is lots of evidence of the climate changing during the prehistoric era and that being associated with changes in the fauna, the ecosystem, and the environments. Some of those changes took place over millions of years and yet they still had a big impact. It is the speed of the changes happening today that is the problem. Many animals cannot keep up.
