Published on March 1st, 2020 | by David Marshall


Episode 108: Plesiosaurs

Plesiosaurs are some of the most easily recognisable animals in the fossil record. Simply uttering the words ‘Loch Ness Monster’ can conjure a reasonably accurate image of what they look like. Thanks to palaeoart, it’s also fairly easy to envision how they lived: swimming through the open Jurassic seas, picking fish, ammonites and belemnites out of the water.

What we don’t imagine are plesiosaurs at the South Pole, nor would we ever picture them swimming amongst icebergs or poking their heads out of holes in the ice to breathe. We’d never think to find them in freshwater either. Even more surprising is that the evidence for this radical vision of polar plesiosaurs is often found preserved in the precious mineraloid opal.

In this interview, we’re joined by Dr Benjamin Kear, Curator of Vertebrate Palaeontology at the Museum of Evolution, Uppsala University in Sweden. He paints for us a picture of life at the South Pole and discusses the importance of polar habitats in driving the evolution of the plesiosaurs.

Plesiosaurs have been known for a relatively long time, with the first publications of their remains as far back as 1719. Numerous discoveries from localities such as Lyme Regis placed plesiosaurs at the forefront of palaeontological research in the infancy of the subject as a science. Image: Wilhelm Dames’ 1895 reconstruction of a plesiosaur showing preserved soft tissues.
Given the quality of their remains and the long history of their research, the classic ‘Loch Ness Monster’ shape of plesiosaurs is easily recognised. Still, new taxa continue to be discovered. Image: A new polycotylid plesiosaur from Richmond in northwestern Queensland. Credit: Benjamin Kear
The plesiosaurs also contain the pliosaurs, which possessed relatively shorter necks and larger heads. Image: Jaws of the gigantic pliosaur Kronosaurus from Richmond in northwestern Queensland. Credit: Benjamin Kear.
Australasia is quickly emerging as an important place to find the remains of plesiosaurs and their discovery is proving to be pivotal in our understanding of the evolution of the group. Image: Reconstruction of the Australian Cretaceous plesiosaur Eromangasaurus. Credit: Josh Lee.
Reconstructed globe showing Australia (part of landmass towards the South Pole) in the Lower Cretaceous Period, some 120 million years ago. Credit: SAPAC.
Rocks deposited at this time are now exposed over vast areas of Australia, such as here, close to Boulia in northwestern Queensland. Credit: Benjamin Kear.
Fossils here can often be preserved by the precious silicate mineral opal. Image: Opalised belemnite from Coober Pedy in South Australia. Credit: Benjamin Kear.
Opal is valued for the iridescent colouration it produces, making it a highly valuable material. Image: Opalised bivalve shell from Coober Pedy in South Australia. Credit: Benjamin Kear.
To meet demand for opal, large areas of land are mined. Image: Opal mines at Lightning Ridge in northern New South Wales. Credit: Henk Godthelp.
Since the majority of opal found in this region is from fossils, large amounts of palaeontological material is extracted. Image: Underground opal mine at Lightning Ridge in northern New South Wales. Credit: Henk Godthelp.
Amongst the oplalised fossils can be found the remains of vertebrates, including dinosaurs and marine reptiles. Image: Opalised plesiosaur tooth from Coober Pedy in South Australia. Credit: Benjamin Kear.
Discovered in Coober Pedy, the plesiosaur Umoonasaurus represents the most completely preserved opalised vertebrate fossil ever found. Credit: Josh Lee.

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