Carnivorous Abelisaur Size Confirmed by Forgotten Fossil

A fossil stashed away in an Italian museum has given scientists a new appreciation for just how big a predatory, carnivorous dinosaur could get.

A forgotten fossil stashed away in an Italian museum has given scientists a new appreciation for just how big a predatory, carnivorous dinosaur called abelisaur must have been.

PhD student Alessandro Chiarenza, then at the University of Bologna and now at Imperial College London, asked officials with the Museum of Geology and Palaeontology in Palermo, Italy if he could examine a fossilized femur that had previously gone unidentified.

After Chiarenza's analysis, it turned out that the bone was from a 95-million-year-old representative of abelisauridae, a group of dinosaurs that had powerfully muscled hind limbs, razor-sharp teeth, tiny forelimbs, and probably feathers.

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The abelisaur Chiarenza studied would have been about 29 and a half feet (9 meters) long and likely weighed 1 to 2 tons, and those numbers have given scientists a better idea of the peak size of these dinos.

"Smaller abelisaur fossils have been previously found by palaeontologists, but this find shows how truly huge these flesh-eating predators had become," said Chiarenza, in a statement. "Their appearance may have looked a bit odd, as they were probably covered in feathers, with tiny, useless forelimbs, but make no mistake: They were fearsome killers in their time."

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The big dino lived in late-Cretaceous North Africa, a tropical world of rivers and mangrove swamps, with plenty of large fish, turtles, crocodiles and other dinosaurs to eat.

The femur came from a fossil bed in Morocco called the Kem Kem Beds, known for containing dinosaur remains from five - now six, including abelisaur - different groupings of predators.

Scientists have long puzzled over how so many predators could have coexisted in the same place without tearing each other to bits.

Chiarenza and University of Bologna colleague Andrea Cau argue that abelisaur and friends actually lived apart from each other, in different environments, and that over time the changing geology of the region mixed the fossils of the different predators together.

"Rather than sharing the same environment, which the jumbled-up fossil records may be leading us to believe," Chiarenza said, "we think these creatures probably lived far away from one another in different types of environments."

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A study on the new findings about this hefty creature have just been published by Chiarenza and Cau in the journal Peer J.

And, as for that drawer that held the forgotten fossil? "Our study shows how museums still play an important role in preserving specimens of primary scientific value, in which sometimes the most unexpected surprises can be discovered," Cau said. "As Stephen Gould, an influential palaeontologist and evolutionary biologist, once said, 'sometimes the greatest discoveries are made in museum drawers'."

Paleontologists have just assembled the most comprehensive family tree of meat-eating dinosaurs. Published in the journal Current Biology, the family tree reveals how diverse carnivorous dinosaurs were and how birds eventually evolved from them. Tyrannosaurs, including

Tyrannosaurus rex

, are one key group on the meat-loving dino family tree. Lead author Steve Brusatte of the University of Edinburgh's School of GeoSciences told Discovery News, "The most iconic dinosaurs of all, tyrannosaurs were more than just the 13-meter-long (nearly 43 feet long), 5-ton monster predator

T. rex

." "Tyrannosaurs were an ancient group that originated more than 100 million years before

T. rex

, and for almost all of their evolutionary history they were small carnivores not much bigger than a human in size."

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"Some of the rarest theropods (two-legged carnivorous dinos) of all, compsognathids are represented by about half a dozen species," Brusatte said. "They were small, sleek meat-eaters which ate small prey like lizards." One of the more recent finds, Juravenator from Germany, is known from a nearly complete fossil.

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Ornithomimosaurs were theropods called "ostrich mimic" dinosaurs -- for a reason. "Like living ostriches, they could run fast on their long legs and used their sharp, toothless beaks to eat a varied diet of small prey, plants, and perhaps even small shrimps in the water just like living flamingos," Brusatte explained. "A recent find in Canada showed that not only were ornithomimosaurs feathered, but they also had complex feathers on their arms that would have formed something of a wing, although they couldn't fly."

Brusatte describes therizinosaurs as "perhaps the weirdest theropods of all." "These were big, bulky, cumbersome dinosaurs that ate plants. They had fat barrel-shaped chests, stocky legs, and big claws on their arms," Brusatte said. For many years paleontologists argued about which group this dinosaur belonged to, only recently settling on theropods. This means they were fairly closely related to birds, despite their weird anatomy.

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Alvarezsaurs were among the smallest dinosaurs of all, measuring just a few feet long and weighing less than 5 kilograms (10 pounds). "Some of them had only a single functional finger on their hand, which they probably used to prod deep into the nests of bugs, which were one of their main food sources," Brusatte said.

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Oviraptorosaurs, were a group of small omnivores that were lightweight, lacked teeth and had tall, hollow crests on their skulls. The recently discovered Anzu -- the so-called "

chicken from hell

" -- came by its nickname honestly. It towered more than five feet tall, weighed more than 400 pounds, and was covered in a coat of feathers.

"Troodontids were probably the smartest dinosaurs of all, as they had the largest brains relative to their body size of any dinosaur group," Brusatte said. "Most troodontids were small, fast-running dinosaurs that probably ate both meat and plants." Among the most recently discovered of this group are the small, feathered Anchiornis and Xiaotingia, which lived in China about 160 million years ago. "They look eerily similar to birds, so much so that some researchers think they could be primitive birds rather than troodontids with wings and feathers," Brusatte said.

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Dromaeosaurids were "raptor dinosaurs" that include Velociraptor from "Jurassic Park" fame. These dinosaurs were pack hunters who wielded a sharp, hyper-extendable "killer claw" on their second toe. "One of the most recently discovered dromaeosaurids is Balaur, a poodle-sized terror from Romania which had not one, but two 'killer claws' on each foot."

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"The oldest birds, like Archaeopteryx that lived 150 million years ago in Germany, are very hard to distinguish from their closest dinosaurian relatives," Brusatte said. "Unlike living birds, they had teeth, sharp claws on their wings, and long tails." "Over the past two decades," he continued, "over 50 new species of Mesozoic birds have been discovered in northeastern China, in the same rock units as the famous 'feathered dinosaurs.' So many birds are preserved here because entire ecosystems were buried by volcanic eruptions, turning animals to stone like a dinosaur version of Pompeii."

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"The 10,000 species of birds that live today -- from hummingbirds to ostriches -- are modern dinosaurs," Brusatte said. "They are dinosaurs in the same way that humans are mammals. The classic body plan of living birds -- feathers, wings, wishbones, air sacs extending into hollow bones -- did not evolve suddenly but was gradually assembled over tens of millions of years of evolution. But, when this body plan finally came together completely, it unlocked great evolutionary potential that allowed birds to evolve at a super-charged rate." "They underwent a burst of evolution early in their history, which eventually led to the 10,000 species alive today -- more than twice the number of mammals."

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