T. Rex, Other Big Dinosaurs Could Swim, New Evidence Suggests

Richard A. Lovett
for National Geographic News
May 29, 2007
Predatory dinosaurs such as the mighty Tyrannosaurus rex could swim, say scientists who claim they have found definitive proof of the behavior.

The evidence, they say, is odd scuff marks found in Cretaceous-era rock in northern Spain's Cameros Basin.

The Cretaceous period lasted from 145.5 million to 65.5 million years ago.

The tracks, which are 50 feet long (15 meters long) and contain 12 prints, suggest that a large animal was scrabbling at the bottom of a 10-foot-deep (3-meter-deep) lake with a swimming, not wading, motion.

The marks were likely left more than one hundred million years ago at the well-preserved La Virgen del Campo site, where scientists have also unearthed more than 10,000 other fossil footprints.

Ripples in the stone show that the dinosaur—possibly a T. rex—was fighting a current, trying not to drift sideways.

The tracks are distinct from known swimmers of the period, such as turtles or crocodiles, and indicate that the animal was a theropod—a carnivore that walked upright.

Theropods include T. rex and numerous smaller dinosaurs, including the velociraptors of Jurassic Park fame.

Tracking a Swim

Scientists have long known that such dinosaurs could wade.

(See related: "Dino-Era Lizard Is Missing Link to Swimming Reptiles, Experts Say" [November 21, 2005].)

But proving they could also swim has been difficult, because an animal that is totally afloat leaves no tracks. So the only way to prove that they could swim is to find footprints left by a dinosaur in contact with the bottom.

"Getting the right conditions is quite rare," said Peter Galton, a retired paleontologist from the University of Bridgeport in Connecticut, who was part of the research team.

Part of what makes the new find interesting, Galton said, is that the footprints are very irregular.

The upstream leg appears to be moving straight ahead, but the other was pushing sideways in an effort to keep the animal from drifting downstream.

Not only do the tracks show that the dinosaur was nearly afloat, but they also indicate the type of swimming motion a T. rex or other theropod might have used.

"It is a style of amplified walking with movements similar to those used by modern bipeds, including aquatic birds," study co-author Loic Costeur of the University of Nantes in France said in a statement.

The study appears in the June issue of the journal Geology.

Long Suspected

The discovery didn't come as a surprise to some.

"This is certainly an interesting find, but dinosaur experts have long accepted that theropods could swim (as can most animals when put in water)," Hans-Dieter Sues, a paleontologist at the Smithsonian Institution, said by email. He was not involved in the study.

Sues noted that in 1980 scientists found tracks in New England's Connecticut River Valley that appeared to be made by a swimming dinosaur.

But study co-author Galton said the New England tracks aren't definitive. Subsequent experiments revealed that lesser rheas, a species of ostrichlike bird, leave very similar footprints when running over nearly dry plaster of Paris. Therapods of the Cretaceous and modern-day rheas have similar physical builds.

Galton acknowledges that nobody really doubted that dinosaurs could swim.

"But this is the first scientific evidence that they could do what you think they could do," he said.

Taking to Water

The Spanish find may help dispel a decades-old myth that large web-footed dinosaurs, called hadrosaurs could escape their predators by taking to the water or swimming to an island.

Herbivorous dinosaurs may still have fled to such places. But, like modern bears, predators could simply swim out after them if they wished, according to scientists.

More information may come from additional swimming dinosaur tracks that have been discovered in Utah, Galton said.

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