Forget the sea monsters of legend. The long-extinct mosasaurs were the real deal

Ancient legends are filled with stories of sea monsters terrorizing people. While we know now that they don’t exist the long-extinct marine reptiles that existed well before humans could be accurately described as sea monsters. Especially one family in particular — the Mosasauridae. These were true sea monsters, terrorizing the ancient seas of the Cretaceous period some 145 to 65.5 million years ago. And recent research shows mosasaurs may have been even more powerful swimmers than previously thought.


One of the largest mosasaurs
Plotosaurus bennisoni was a powerful swimmer. Illustration by Nobu Tamura license CC SA 4.0 via Wikimedia Commons

There were many species and subspecies in this impressive family. Some, like Dallasaurus at less than a meter in length, were rather small. Others, however, were truly stupendous, reaching lengths of 50 feet (15.2 meters), LiveScience reports. With enormous skulls resembling those of their modern relatives — monitor lizards (think Komodo dragon), elongated bodies and alligator-like tails, these massive creatures had powerful jaws lined with two rows of sharp teeth. And despite their enormous size and bulk, these aquatic lizards could still swim incredibly fast.


Mosasaurs had formidable skulls
The formidable skull of the mosasaur Plioplatecarpus license by Tim Evanson license CC SA 2.0 via Wikimedia Commons


There’s a good chance this may be due to a powerful breast-stroke. Scientists have long wondered how such massive creatures could move so quickly to ambush their prey. So researchers from the Natural History Museum of Los Angeles County analyzed fossils of one mosasaur in particular: Plotosaurus. This genus featured a more streamlined, fusiform body, thinner flippers, and an especially powerful tail fin.


Mosasaurs were swift predators
Another illustration of P. bennisoni featuring the huge creature’s elongated body and powerful tail. Illustration by Dmitri Bogdanov license CC 3.0 via Wikimedia Commons

Scientists have long understood that these ancient sea monsters had large and powerful pectoral girdles (the bones that supported those paddle-like forelimbs). There’s a wellspring of research that shows Plotosaurus and its kin used their powerful tails to propel themselves through the water over long distances, but by examining the museum specimen and using measurements of the pectoral girdle that were collected by earlier researchers, the scientists soon realized it supported numerous muscle attachments. Not only that, the pectoral girdle was asymmetric. This is a surefire sign that Plotosaurus likely used a strong, inward pull-down motion known as adduction, Eurekalert reports. So analysis suggests mosasaurs performed a sort of breast-stroke motion with those paddle-like forelimbs, enabling them to propel themselves rapidly in short bursts.


Mosasaurus hoffmani. Illustration by RobinGoodfellow_(m) license Public Domain via Flickr

So thanks to that massively strong tail, these creatures were powerful long-distance swimmers that also excelled at using short-distance sprints thanks to those powerful forelimbs. And this makes mosasaurs unique among four-limbed creatures whether living or extinct.

“Like anything that swims or flies, the laws of fluid dynamics mean that burst versus cruising is a trade-off,” said co-author Mike Habib, assistant professor of anatomical sciences at the University of Southern California, in the statement. “Not many animals are good at both.”

Mosasaurs enjoyed a worldwide distribution and they had plenty of competition for food from other enormous marine reptiles, including plesiosaurs, which are noted for their extremely long necks, and the superficially dolphin-like ichthyosaurs.

Plesiosaurs competed with mosasaurs
The Cretaceous plesiosaur Thalassomedon hanningtoni. Illustration by Dmitry Bogdanov license CC SA 4.0 via Wikimedia Commons
The Cretaceous ichthyosaur Platypterigius longmani. Illustration by Dmitry Bogdanov license CC 2.5 via Wikimedia Commons

But despite all these large reptiles, there was plenty of prey to keep them busy, reports. There was no shortage of fish, and mosasaurs also preyed on ammonites (extinct relatives of the modern-day nautilus), and cuttlefish.


Illustration of the mosasaur Plioplatecarpus by Dmitry Bogdanov license CC SA 3.0 via Wikimedia Commons

Despite their obvious success, mosasaurs, along with nearly all of the dinosaurs (except birds) became extinct during the K/T Extinction event 66 million years ago, when nearly 80 percent of life on Earth was wiped out. Mosasaurs were also facing increased competition from sharks like Cretoxyrhina, which were faster, sleeker, and potentially more intelligent, ThoughtCo. reports.


As magnificent as these reptiles were, we can probably be glad they became extinct before we evolved to worry about them. Some of them were large enough to swallow us whole, after all.


The research has yet to be peer-reviewed. It was presented at the annual 2019 meeting of the Geological Society of America, in Phoenix Arizona.


Want to know more about these fascinating reptiles? Check out the video below.


Featured image courtesy of the video above

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