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The softer side of mosasaurus

Illustration by Julius T. Csotonyi

The legendary mosasaurus has a star turn coming this summer, as the face of “Jurassic World,” the latest Jurassic Park movie. The gigantic Mesozoic-era marine lizard is a made-for-Hollywood creature, with an agile, predatory body that grew to more than 50 feet long and the ability to gobble sharks like popcorn shrimp. Now, thanks to a serendipitous discovery at Yale, published in the May issue of the journal Paleontology, we also know another amazing feature of mosasaurs: They likely gave birth to live young in the middle of the ocean.

For a long time, paleontologists have hypothesized that mosasaurs had live births, but they lacked real proof. Then in 2012, Daniel Field opened a drawer of fossilized bird bones at the Peabody Museum of Natural History at Yale and instantly recognized several that didn’t belong.


“I saw them and immediately knew they weren’t birds, so I talked it over with a few other paleontologists at Yale and came to a consensus pretty quickly,” says Field, a graduate student in vertebrate paleontology at Yale. “They appear to be the smallest mosasaur remains that we know of.”

The fossils from two baby mosasaurs that Field stumbled upon had been dug up more than 100 years earlier in the center of a paleontological site known as the Niobrara Formation in western Kansas. When mosasaurs were still swimming around, the Niobrara was an ocean, and the tiny mosasaur fossils were found hundreds of miles away from what would have been the closest shoreline. To Field and others, this strongly suggests mosasaurs “probably lived and died in open ocean setting, they were probably born alive.”

Beyond establishing how mosasaurs gave birth, Field hopes the fossils will provide insight into how they grew from bird-sized newborns into dino-scale adults. In a less scientific vein, he says he enjoys how, “this kind of discovery makes it easier to envision these ancient creatures as living, breathing organisms.” It’s the kind of soft perspective that might be useful to keep in mind as you watch mosasaurs wreak havoc in movie theaters this summer — when they weren’t snatching pteranodons from the sky and snacking on great whites, mosasaurs may have been off having their own little miracle in the middle of the ocean.


Kevin Hartnett is a writer in South Carolina. He can be reached at kshartnett18@gmail.com.


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