Why are all the biggest dinosaurs found in Patagonia?

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Oct. 17 2007 6:48 PM

Giant Dinosaurs in Argentina

Why are the biggest fossils found in Patagonia?

"Futalognkosaurus dukei" bones. Click image to expand.
Argentine paleontologists show replicas of Futalognkosaurus dukei bones

Paleontologists announced on Monday that they had discovered the remains of a 105-foot-long dinosaur on the banks of a lake in the Argentine portion of Patagonia. The Futalognkosaurus dukei ranks among the largest known dinosaurs, along with two other species whose remains were discovered in Patagonia, the Argentinosaurus and Puertasaurus reuili. Why are all the biggest dinosaurs found in Patagonia?

They died at the right time in the right place. Patagonia happens to be an excellent place to find fossils from the Cretaceous Period, when dinosaurs reached their largest sizes. (The extinction of the dinosaurs occurred at the end of the Cretaceous, about 65 million years ago.) Because of natural uplift and erosion, sediment that dates from this time is exposed at the surface in the region's desert badlands. This makes fossilized bones easier to spot and excavate. (Fossils are also easy to find in the badlands of the Dakotas, Wyoming, and Montana, as well as in Mongolia's Gobi Desert.)

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The three giant dinosaurs found in Patagonia are all titanosaurs, a kind of long-necked sauropod that happened to get very big in South America. Since South America was its own continent for most of the Cretaceous Period, much of its plant and animal life evolved distinctly from that of the other land masses. Its isolation could have been responsible for spurring sauropods to grow larger than those found on other continents, but there's no scientific consensus as to exactly how this happened. (In contrast, large mammal populations tend to shrink in size when they evolve in isolation.)

Sauropod remains aren't found just in South America. So far, specimens have been discovered on every continent except Antarctica, where the fossil rock sediment isn't readily accessible. Excavators have even found evidence of the biggest sauropods—i.e., the titanosaurs—in North America, Australia, and Madagascar. It's possible that as paleontologists excavate more sites rich in Cretaceous fossils, like those in India, China, and sub-Saharan Africa, larger dinosaur remains will be discovered. But as of yet, none of those areas has yielded any animal as big as those discovered in Patagonia.

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Explainer thanks Richard Kissel of Chicago's Field Museum, Diego Pol of Argentina's Museo Paleontológico Egidio Feruglio, and Jeff Wilson of the University of Michigan.

Morgan Smith, a former Slate intern, is a law student in Austin, Texas.