Prehistoric Superpredator: Weird Whatcheeria Was the “T. rex of Its Time”

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Prehistoric Superpredator: Weird Whatcheeria Was the “T. rex of Its Time”

Whatcheeria was a prehistoric superpredator. It was a six-foot-long lake-dwelling creature with a salamander-like body and a long, narrow head. Credit: Adrienne Stroup, Field Museum

Ancient Iowan superpredator got big by front-loading its growth in its youth.

Fossils found only at the Field Museum reveal the growth history of Whatcheeria.

A Whatcheeria skull in the collections of the Field Museum, with its many sharp teeth visible. Credit: Kate Golembiewski, Field Museum

That’s because Whatcheeria was a top predator. Bony grooves in its skull for sensory organs shared by fish and aquatic amphibians reveal that it lived underwater, and its sturdy leg bones could have helped it hunker down in one spot and wait for prey to swim by. “It probably would have spent a lot of time near the bottoms of rivers and lakes, lunging out and eating whatever it liked,” says Otoo. “You definitely could call this thing ‘the T. rex of its time.’”

Co-author Ben Otoo standing by a life-size illustration of a large Whatcheeria specimen at the Field Museum. Credit: Courtesy of Ben Otoo

Co-author Ken Angielczyk with a drawer of Whatcheeria specimens behind the scenes at the Field Museum. Credit: Kate Golembiewski, Field Museum

“Examining these fossils is like reading a storybook, and we are trying to read as many chapters as possible by looking at how juveniles grow building up to adulthood,” said Megan Whitney, the study’s lead author, a professor at Loyola University in Chicago who began working on the project at Harvard University. “Because of where Whatcheeria sits in the early tetrapod family tree, we wanted to target this animal and look at its storybook at different stages of life.”

Some of the many drawers containing Whatcheeria specimens and other fossils from the Iowan quarry where the animal was discovered. Credit: Kate Golembiewski, Field Museum

“I have a very distinct memory of jumping on Slack with Stephanie Pierce and saying, this breaks all of the rules that we thought of for how growth is evolving in these early tetrapods,” said Whitney.

However, there’s a trade-off: growing really big really fast takes an enormous amount of energy, which can be a problem if there’s not enough food and resources for the growing animal. It’s easier to get just enough food to get a little bit bigger, the same way it’s easier to make smaller monthly rental payments than it is to save up for a big downpayment on a house.

In addition to helping give us a better sense of the evolutionary pressures on early tetrapods, researchers say the findings are a reminder that evolution isn’t a neat stepwise process: it’s a series of experiments.

 “Evolution is about trying out different lifestyles and combinations of features,” says Angielczyk. “And so you get an animal like Whatcheeria that’s an early tetrapod, but it’s also a pretty fast-growing one. It’s a really big one for its time. It has this weird skeleton that’s potentially letting it do some things that some of its contemporaries weren’t. It’s an experiment in how to be a big predator, and it shows how diverse life on Earth was and still is.”