Aug. 27, 2008 -- Recently excavated dinosaur bones reveal that the most common large predatory dinosaurs in South America during the Cretaceous period were the abelisaurids, a group that included some of the most well-armed and fierce-looking carnivores that ever lived.
The new fossils -- the first-ever dinosaur bones to be unearthed at the Marilia Formation in Bauru Basin, Brazil -- could belong to one or more new species, but paleontologists suspect they may be the remains of Carnotaurus sastrei, a dinosaur that, in recent years, has become one of Hollywood's favorite animal villains.
"The best known and most spectacular abelisaur is Carnotaurus, the villain in the Disney movie 'Dinosaur,'" said lead author Fernando Novas.
"It combined the horns of a bull above a very stubby face, with forelimbs that were even shorter than those of Tyrannosaurus," added Novas, a paleontologist at the Argentine Museum of Natural Sciences in Buenos Aires. "Carnotaurus had a stout, muscled neck and could swing its head with great power and fury."
He continued that the dinosaur's head and large horns "were probably used to butt other meat-eaters away when they gathered around a carcass."
Abelisaur bones and teeth have been found at other South American sites in recent years, most notably the remains of a Pycnonemosaurus in southern Argentina. That carnivore possessed a distinctive hatchet-shaped head crest.
The new bones, belonging to three separate individuals, intriguingly were found in association with two sauropods, Trigonosaurus pricei and Baurutitan britoi, both of which were big plant-eaters that the abelisaurs likely feasted upon. The fossils for the carnivores were also discovered alongside two crocodylomorphs -- ancient relatives of crocodiles -- a maniraptoran ("hand-snatcher") dinosaur bone, and the freshwater turtle Cambaremys langertoni.
Together, the fossils are allowing researchers to gradually piece together South America's Cretaceous ecosystem from 135 to 65 million years ago. The relative plethora of abelisaur bones and teeth versus those of other dinosaur carnivores led to this group being placed at the top of the food chain.
The findings are published in the latest issue of Cretaceous Research.
"Although abelisaurids were predators, it's not possible to assure if they were active hunters, scavengers or both," co-author Ariel Mendez told Discovery News.
Mendez added that while abelisaurs once dominated the continent, they might not have been without enemies.
"Other groups of theropods (meaning "beast-footed" carnivores) that populated South America during the Cretaceous include coelurosaurs and carcharodontosaurs that could have been possible competitors for food and territory," he said.
Since similar dinosaurs, including near-identical abelisaurs, have been found in Africa, Madagascar and India, it's possible that these land masses, perhaps excluding Africa, retained connections well into the Late Cretaceous, according to Scott Sampson, chief curator of the Utah Museum of Natural History.
"If so," he said, "dinosaurs may have been able to disperse across the vast distances between South America and India-Madagascar via an intervening Antarctica."
Novas agreed, and further thinks the Northern and Southern Hemispheres also became disconnected during that time, which allowed for an unusual division of predators.
He explained, "While tyrannosaurs and velociraptorids dominated the northern continents, abelisaurs were the most common predators in the southern continents."
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