This Cretaceous 'Sea Monster' Attacked Prey Faster than Great White Sharks
By analyzing tail length and muscle power, paleontologists have explained the physics behind a mosasaur's deadly ability to lunge toward its prey.
Ever since the first well-preserved mosasaur skeletons were found in the late 1800s, paleontologists have recognized that these flippered sea lizards lived in the ocean. But their tails showed no sign of the specializations seen in sharks or dolphins, leading many to assume the marine reptiles sculled under the waves like giant crocodiles or eels. Because this serpentine swimming style creates a lot of drag underwater — especially at large sizes — researchers concluded that mosasaurs weren’t efficient swimmers.
But in the 2010s, a reassessment of mosasaur anatomy suggested they had relatively stiff bodies, and one study showed that their tails ended in a shark-like tail fin. This body plan makes for a much more efficient swimmer, like the difference between a human launching from a pool wall versus starting to swim from treading water.
“They were probably much more efficient and dynamic swimmers than previously thought,” says Kiersten Formoso, a vertebrate paleontologist at Rutgers University in New Jersey.
A functional morphologist interested in biomechanics, Formoso wondered how efficient those tails could be. She and her colleagues combined fossil measurements with mathematical modeling to estimate how fast a mosasaur could lunge forward — and how members of its family adapted to different predatory lifestyles. Their study, published Wednesday in the journal Current Biology, found that some mosasaurs could potentially rocket through the water at a powerful 15 miles an hour.
“People really underestimate the scariness of a forward lunge,” Formoso says. “Getting caught in the lunge of one of these mosasaurs would be like getting hit by a car, or even a bus.”
The finding offers insight into the diverse hunting strategies of some of the largest and most powerful reptilian predators ever to swim the seas.
Mosasaurs come in two slightly different families. One lineage, called Russellosaurines, has relatively long tails and V-shaped snouts. The other, called mosasaurines, has proportionally shorter tails and heavier snouts. The team measured the skeletons of two specimens from each family. For the long-tailed lineage, they examined the fearsome Tylosaurus proriger and the smaller, speedy-looking Platecarpus. Representing the shorter-tailed mosasaurs were Plotosaurus — the skeleton of which Formoso measured hanging from the ceiling of the Natural History Museum of Los Angeles County — and an undescribed species of Mosasaurus, the genus that lent the whole family its name.
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In addition to physically measuring the fossil animals, Formoso and her colleagues also digitally scaled up their measurements to represent the titans of the family: the enormous, humpback-whale-sized Tylosaurus rex and Mosasaurus hoffmannii.
They found that the long tails of mosasaurs like Platecarpus and Tylosaurus let their tail fins curl further before snapping back, propelling them through the water in sudden bursts — and making them the fastest accelerators of the bunch. With a single flick of its mighty tail, a 45-foot-long leviathan like Tylosaurus rex could potentially lunge at around 15 miles per hour, or 23 feet per second. By comparison, great whites — the largest modern predatory sharks — can manage a burst of about 11 miles per hour, or 16 feet per second, enough to propel them out of the water in spectacular breaches after seals.
While all four mosasaurs the team examined may have moved at different speeds, Platecarpus was the zippiest, with Tylosaurus proriger second, followed by Mosasaurus and then Plotosaurus.
Formoso says her findings support a longstanding suspicion — based on tooth wear patterns and head anatomy — that long-tailed mosasaurs like Platecarpus and Tylosaurus were likely ambush predators, lurking along the bottom of shallower oceans before lunging up in a burst to snatch big fish, plesiosaurs, and smaller mosasaurs.
But the other branch of the family was no slouch, either: the team found that while Mosasaurus and Plotosaurus couldn’t lunge as fast — perhaps around 13 or 16 feet a second — their shorter tails were ideal for cruising efficiently through deeper, open-ocean environments. That suggests they may have hunted like modern open-ocean predators such as tuna, mako sharks, and swordfish.
“The mosasaurines are not slow at all,” Formoso says. “I would not want to be a couple of meters away from a Mosasaurus even now, with the knowledge that I have.”
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While they weren’t as quick to accelerate, short-tailed mosasaurs seem to have had an advantage over their longer-tailed cousins, says Mike Polcyn, a mosasaur expert at Southern Methodist University not involved in the study.
The Mosasaur fossil record suggests that the long-tailed lineage was the first to get big. They quickly took over shallow seas, in part because of their fearsome ambush habits. The shorter-tailed mosasaurines therefore had to go where the long-tailed ones weren’t, Polcyn says. That led them to evolve a different hunting strategy: chasing prey over longer distances.
“That sustained swimming performance as a pursuit predator instead of an ambush predator might have ultimately led to the demise of Tylosaurus in favor of the large Mosasaurus,” Polcyn says.
Amelia Zietlow, a paleontologist at the History Museum of the Castle in Wisconsin, praised the study, calling it “a valuable contribution to how we understand mosasaurs as once living, breathing animals.”
The work is just getting off the starting block, says Formoso, since researchers can apply the same methods to other mosasaurs, like the big-toothed Prognathodon or the portly, shell-crushing mosasaur Globidens. Researchers could also use it on elusive modern sea animals like Sei whales, she adds. These giants are hard to study in the wild, but scientists have their skeletons.
“They’re large predators, so they’re very important components of their respective ecosystems,” Formoso says. “Understanding how they operate is really cool.”
