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 remainsall of them indicative of freshwater bodiesas 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.
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 activerunning, et ceterathat 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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