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Dinosaur Discovered in Patagonia—Named "Small Head"

John Roach
for National Geographic News
April 5, 2004
 
Argentine paleontologists have discovered a 13-foot (4-meter) plant-eating dinosaur with a long neck and small head that roamed the southern tip of South America about 70 million years ago.

The team, led by Fernando Novas of the Argentine Museum of Natural Sciences in Buenos Aires, named the dinosaur Talenkauen santacrucensis. Talenkauen means "small head" in the Aonikenk Indian language.


Talenkauen was an ornithischian—dinosaurs that had birdlike hips. Its closest relatives include Hypsilophodon, a quick and agile dinosaur that lived 125 million years ago in Europe, and Iguanodon, a 33-foot (10-meter) herbivore that lived about 125 million years ago in Europe and North America.

The partially preserved skeleton of Talenkauen was found in 2000 in the Patagonia region on a hillside near the southeastern shore of Viedma Lake in Argentina's Santa Cruz Province. The public announcement of the discovery last Friday coincided with publication of a scientific description of the dinosaur in the Argentine paleontology journal Ameghiniana.

Talenkauen was one of just a few ornithischians known from the Cretaceous period in South America. The Cretaceous is what geologists call the period of 144 million to 65 million years ago. It was toward the end of the age of dinosaurs, when modern mammals and birds, flowering plants, and insects started to emerge.

The new find sheds light on the diversification of the plant-eating ornithischians in the southern continents, Novas said.

Patricia Vickers-Rich—a paleontologist from Monash University in Australia who has extensively studied dinosaurs from the southern continents—said the find of Talenkauen is an important contribution to understanding the region's taxonomy (scientific classification of plants and animals).

"In this region there are lots of sauropods but not much else [other than] an occasional theropod. To get one in the group Fernando has is most unusual and significant," Vickers-Rich said.

Titanosaurian sauropods were huge plant-eating dinosaurs with long necks and tails like the Jurassic apatosaurs. Theropods were meat-eating dinosaurs with short arms and powerful legs.

The research by Novas and colleagues Andrea Cambiaso and Alfredo Ambrosio is supported by grants from the National Geographic Society's Committee for Research and Exploration and Argentina's National Council of Scientific and Technical Research and National Agency for Scientific and Technological Promotion. Fieldwork was also supported by the Renault and Nissan motor companies of Argentina.

Forest Environment

Novas and his colleagues discovered Talenkauen among an abundance of petrified logs of large evergreen trees, which suggests the dinosaur roamed in a forested landscape.

Hans-Dieter Sues, associate director for research and collections at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., said ornithischians filled a niche in this landscape as low-level grazers.

"Ornithischians fed on vegetation closer to the ground and chewed up their plant food, unlike sauropods, which ingested large amounts of plant food that was ground up in a muscular gizzard filled with stones and which could feed at levels higher off the ground, perhaps even in the canopy," Sues said.

Sues is a member of the National Geographic Society's Committee for Research and Exploration.

Close to both the Atlantic and Pacific coasts, during the Cretaceous period southern Patagonia was repeatedly flooded and at times underwater. The occasional presence of ocean water is recorded in marine sediments that are above and below the continental sediments in which Talenkauen and other fossils were found.

"The beds in which Talenkauen was found also include teeth of lungfishes and turtle and crocodile remains—all of them indicative of freshwater bodies—as well as isolated bones or part of skeletons of giant plant-eating dinosaurs and the meat-eating theropods," Novas said.

By the late Cretaceous, South America was separated from Antarctica by a shallow straight and the dinosaurs from the two landmasses could not easily mingle.

The Cretaceous dinosaurs from South America were dominated by the herbivorous titanosaurs, which were bulky sauropods. This holds true even as far south as Santa Cruz Province, where Talenkauen, an ornithischian, was found.

"Contrary to expectations, the Cretaceous record of Antarctic dinosaurs does not include at the moment any titanosaur remains, but it does ornithischians," Novas said.

Platelike Structures

The most unusual aspect of Talenkauen is the presence of platelike structures on both sides of the chest. Such plates on dinosaurs are only known for Thescelosaurus neglectus, a hypsilophodontid from North America. Hypsilophodontids were swift, gazelle-like, plant-eating dinosaurs that ran in herds.

Though similar structures, technically known as uncinate processes, are common to many birds and crocodiles today, the presence and development of these platelike structures in dinosaurs, crocodiles, and lizardlike tuataras is far from understood, Novas said.

"However, I presume that Talenkauen had well-developed intercostal [between-the-rib] muscles that participated in the thoracic movements for lung ventilation, as they do in living birds," Novas said.

Talenkauen's plates are too frail and specifically located in the chest to offer protection from predators, unlike the thick plates on armored dinosaurs such as the ankylosaurs, said Novas. In addition, Talenkauen's plates overlap each other. On modern birds the structures are modest and do not overlap.

Vickers-Rich suggests the plates may have helped protect the dinosaurs' innards during activity like running.

"In birds [such plates] stabilize the rib cage, so that the lungs and innards don't get crushed when the bird is flying," Vickers-Rich said. "So part of the story might be to stabilize the thoracic cage/cavity when the animal was active—running, et cetera—that there was not crushing of the innards."

According to Sues, Talenkauen's plates are not uncinate processes, as they are unlike those in birds and predatory dinosaurs like Velociraptor, a speedy, two-legged, meat-eating dinosaur that lived in Asia about 85 million years ago.

"Their function is uncertain, because there is no analogous structure in a present-day animal," Sues said.

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