The Legend of the Sea Serpent Mosasaurus

Mosasaurus as it may have looked when it swam in Earth’s seas 70-65 million years ago.
Image Credit: Dmitry Bogdanov,

The idea of a large, serpentine like animal living in the depths of the ocean and battling heroes of legend has been a favourite tale of a whole host of myths and legends. Since early human history people seem to have been attracted to the idea of such an animal, quite unlike anything that lives today. Even in recent times this is a concept that has people enthralled. Just ask anybody who is convinced that there is a plesiosaur like animal living in Loch Ness. However while a large sea serpent probably doesn’t exist today (not counting real life sea snakes) there was a similar beast that ruled the seas of the Late Cretaceous period 70 million years ago. Its full scientific name, is Mosasaurus hoffmanni (Meaning “Hoffmanns Meuse Lizard”).

Mosasaurus was discovered back in 1764 near the town of Maastricht in the Netherlands. This was a time when the word “dinosaur” hadn’t been spoken yet, and proper scientific research on fossils was in its infancy. The fossil itself was a disarticulated skull, a cast of which is on display in the Sedgwick Museum in Cambridge. This fossil went through an eventful journey before it was first scientifically examined in the early 19th century, which includes being hidden from French occupation and being traded (allegedly) for 600 bottles of wine! Scientists of the time, including the famous French naturalist Georges Cuvier, correctly deduced that this animal was a reptile. Now “Meuse Lizard” may seems like a weird name to give an animal like this, but it was named after the Meuse River which runs through Northern Europe close to Maastricht.

This sea faring animal was very much the top predator of its day, reaching up to 15.2 metres long and weighing 15 tons. While there were other formidable hunters around (one example being Xiphactinus, a 5 metre long predatory fish known for swallowing prey whole!) there was no other marine predator that could rival it. Mosasaurus was an opportunistic hunter, eating almost anything that it could fit its powerful jaws around. This included a whole range of marine animals, from fish to squid, other marine reptiles and even smaller species of Mosasaurs! Mosasaurus was also quite different from other marine reptiles in that its lizard ancestors took to the water at a much later date than other marine reptiles such as Ichthyosaurs and Plesiosaurs. Also, unlike its lizard ancestors Mosasaurus gave birth to live young instead of laying eggs (just like modern day sea snakes). However Mosasaurus, along with the rest of its family, could not survive the asteroid that struck the earth 65 million years ago, dying out alongside the dinosaurs. They are survived by their closest living relatives; monitor lizards and snakes. Which funnily enough makes the sea serpent comparison even more fitting!

The fossilised head of Mosasaurus, showing its frightening battery of teeth!
Image Credit: Tim Evanson,

In the last couple of years Mosasaurus has been getting attention both in film, where it steals the show in the film Jurassic World, and in the world of paleontological research. This research has changed our understanding of how Mosasaurs both looked and behaved, with the following three studies being particularly insightful:

First. A study carried out by Johan Lindgreen, Hani Kaddumi and Michael Polycin in 2013 discovered a new anatomical feature in Mosasaurs. Previously it had been thought that they powered their long bodies through the water with a broad, straight tail, moving in a undulating manner like a modern day sea snake. However, after examining a fossil Mosasaur, named Prognathodon, from Jordan in Africa the palaeontologists noted that the outline of its skin had been fully preserved. This impression clearly showed a tail fluke like those of sharks or Ichthyosaurs, albeit with the upper fluke being smaller than the lower fluke. This tail, a product of convergent evolution, would have enabled mosasaurs to perform fast, powerful strokes to catch prey by surprise.

Second. A study in 2014, carried out by a team of palaeontologists based at Lund University in Sweden (which also included Lindgreen and Polycin, among others), gave us our first look at the colour of a mosasaur. This was an exciting find as evidence of colour is very rarely preserved in extinct animals and had never before been seen in a marine animal. The study looked at tiny blob like structures on the skin of an 85 million year old fossil mosasaur named Platecarpus tympaniticus. These had previously been thought to be bacteria. However as it turns out these blobs were actually melanosomes, the cells that produce skin colour. The structure of these preserved melanosomes showed that this mosasaur, and by extension other mosasaurs such as Mosasaurus, had what is known as “countershading”. Countershading is a colouration pattern that consists of a dark upper body and a light lower body (an example of this being the colouration of a modern day Killer Whale). This has a few advantages; it provides camouflage against the dark ocean depths (when looked at from above) and against the sunlight lit surface (when looked at from below). The dark upper surface also allows the mosasaur to absorb more heat from the sun when it surfaces for air and gives it protection from UV light when at the surface.

Third. A recent study conducted at the University of California, and only published in September 2019, looked in detail at how Mosasaurs swam. What they found was that Mosasaurs could perform a “breaststroke” like action with their front flippers. In conjunction with powerful beats of their tails, this would have allowed them to achieve great bursts of speed through the water. This is interesting because it was thought that marine animals swim using either their tails or their fins, but not both at the same time. As a result this swimming style is unlike any other known animal and makes mosasaurs even more remarkable.

And so, thanks to studies both old and new, we have a detailed picture of Mosasaurus, and its family, as one of the most unique sea faring animals ever. It further proves that the world of paleontological research is still capable of putting fresh spins on iconic animals of the past!

Mosasaurus enjoying a dinosaur dinner!
Image Credit: Jonagold2000,

References/Further Reading

Lindgren, Kaddumi & Polcyn 2013 paper about Mosasaur tail flukes.

Lindgren, J., Kaddumi, H. & Polcyn, M. Soft tissue preservation in a fossil marine lizard with a bilobed tail fin. Nat Commun 4, 2423 (2013).

Lindgren et. al. 2014 paper about Mosasaur coloration. This study also discovered the colour of a 55 million year old turtle (which had the same colour as a modern day leatherback turtle) and a 200 million year old Ichthyosaur (which was a dark colour).

Lindgren, J., Sjövall, P., Carney, R. et al. Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles. Nature 506, 484–488 (2014).

A paper, written by Kiersten Formoso and published in September 2019 (Formoso 2019), on new theories on Mosasaur swimming motions.

Formoso, Kiersten K., Reassessment of the Mosasaur pectoral girdle and its role in aquatic locomotion, Geological Society of America Abstracts with Programs. Vol. 51, No. 5, (2019), doi: 10.1130/abs/2019AM-333823

Further information, from the FossilEra website, about Mosasaur size, diversity, lifestyle and history of discovery

FossilEra “Mosasaurus & Mosasaurs”, FossilEra,

One thought on “The Legend of the Sea Serpent Mosasaurus

  1. Jason R. Abdale 28th Sep 2020 / 6:38 pm

    Mosasaurs are my favorite prehistoric marine creatures. Thank you for posting this article.

    Liked by 1 person

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