Unprecedented fossils reveal the smallest titanosaur ever found

A new dinosaur discovered in Patagonia is among the smallest of giants. Named Titanomachya gimenezi, the long-necked herbivore belonged to a family of usually immense dinosaurs called titanosaurs. But even fully grown, Titanomachya was about the size of a cow—albeit, a very hefty cow.

The new dinosaur was uncovered by Museo Paleontológico Egidio Feruglio paleontologist and National Geographic Explorer Diego Pol and his colleagues as part of their scientific quest to understand how the end of the age of dinosaurs played out in South America. To date, the majority of what paleontologists know about the last days of the dinosaurs—a period known as the late Cretaceous—stems from fossil finds from the Northern Hemisphere, and in particular, North America.

But as Pol and other paleontologists working in South America are demonstrating, the continent has several crucial fossil hot spots that are yielding untold new species and a more detailed view of life in the few million years before the catastrophic asteroid impact that ended the Cretaceous with a bang some 66 million years ago. (Learn more about how scientists are reimagining dinosaurs.)

This new titanosaur is the latest find from the region. So far, Pol and his colleagues have uncovered more than 20 fossil-rich sites dating to the late Cretaceous in Argentina. And one of them—the La Colonia Formation of central Patagonia—is where the researchers found a smattering of bones from a long-necked sauropod. No sauropods had ever been found before in this formation.

“Prior to this discovery, there were no records of sauropod dinosaurs in this region,” Pol says. The find was described April 11 in the journal Historical Biology.

Solving the puzzle

Piecing the dinosaur together was like solving a giant jigsaw puzzle, the researchers say.

“The remains were disarticulated but placed very close to each other,” Pol says.

Back at the lab, the team found they had uncovered ribs, vertebrae, limb bones, and part of a hip. They named the reptile Titanomachya gimenezi after the moment the Olympians battled the titans in Greek mythology, known as the Titanomachy, and the work of paleontologist Olga Giménez.

Despite having just one partial skeleton, the bones are distinct enough from other dinosaurs to justify the new-species distinction, says Universidad Maimónides paleontologist Pablo Gallina, a National Geographic Explorer who was not involved in the new study. Particularly striking is just how small this new dinosaur is.

“When one thinks of these titanosaur sauropods, a large dinosaur with a long neck and tail comes to mind,” Gallina says. “Especially from Patagonia where the largest titanosaurs are found and reach 70 tons.” This dinosaur is just a fraction of the size.

From the dimensions of the fossilized limb bones, Pol and his co-authors estimate that Titanomachya weighed between five and 10 tons, but with the body dimensions of a large cow and a long neck and tail, reaching about 20 feet in length—so about the same length as a minibus. 

That is absolutely puny compared with other titanosaurs. The biggest titanosaurs were more than a hundred feet in length and weighed more than 70 tons. Titanomachya was a relative pipsqueak roaming what’s now Argentina near the very end of the Cretaceous around 67 million years ago.

The world of Titanomachya looked very different from the Patagonia the paleontologists know today. Back in the Late Cretaceous, Pol says, the area was dotted with coastal lagoons and estuaries. It was a wet and marshy place, stalked by the “meat-eating bull” Carnotaurus, and an ensemble cast of other diverse dinosaur species that paleontologists are only just now beginning to understand. Other expeditions to the La Colonia Formation where this titanosaur was found have, so far, turned up duck-billed hadrosaurs, armored ankylosaurs, and more. Titanomachya is perhaps just the tip of a fossil iceberg. 

Why Titanomachya was so small, however, is a mystery. “The body size is particularly striking, not only for this species but also for other titanosaurs that lived in Patagonia towards the end of the Cretaceous,” Pol says.

Experts are investigating several hypotheses for its minuscule size—including that its smallness was a result of titanosaurs adapting environmental pressures.

“One possibility is the reduction of available land area due to the transgression of the Atlantic Ocean that covered large extents of Patagonia,” Pol says. About half of Patagonia’s land area was once blanketed by shallow sea. Paleontologists have evidence from other fossil sites, such as the remnants of Cretaceous islands in what’s now Transylvania, that show sauropod dinosaur species sometimes evolve to be smaller to help them survive in tight spaces with less food.

Other environmental changes might have played a role as well. “Significant changes in ecosystems and climate could have affected the size of titanosaurs,” Pol says. Researchers studying the region’s fossils will continue to investigate this question, though.

Zooming in

More fossils will help reveal broader environmental trends. To paint that picture, they will need to involve far more diverse species than dinosaurs. “We believe we are just beginning to uncover the world of the end of the Cretaceous in Patagonia,” Pol says.

 “Our project focuses not only on dinosaurs but also on plants, invertebrates, and other animal groups.” Ultimately, he wants to help create a detailed picture of Cretaceous ecosystems before they were wiped away by disaster.

Such a holistic view of life in the years before the asteroid impact that ended the age of the dinosaurs is, in turn, essential to understanding how the world changed as a result of that mass extinction event.

“The end-Cretaceous extinction was a global biodiversity crisis,” Pol says, which requires evidence from around the world to understand.

In Cretaceous-era Patagonia, for example, paleontologists are finding evidence that the land, flora and fauna were undergoing significant changes. Titanosaurs like Titanomachya were beginning to disappear, while other herbivores, such as hadrosaurs and ankylosaurs, were taking up new roles in the ecosystem. Ultimately, this tiny titan marks a shift that would end with one of the greatest calamities of all time.

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