Image: Reconstructed skeleton of abelisaurid Majungasaurus crenatissimus
Background photo by Joseph J. W. Sertich; 3D reconstruction by Sara H. Burch; composition by Lucille Betti-Nash
The bizarre forelimb and shoulder girdle of abelisaurid theropod dinosaurs are highlighted in the reconstructed skeleton of Shown here, a reconstructed skeleton of the abelisaurid Majungasaurus crenatissimus from the Late Cretaceous of Madagascar, with the bizarre forelimb and shoulder girdle highlighted.
By LiveScience Contributor
updated 5/22/2012 7:36:17 PM ET 2012-05-22T23:36:17

A newfound giant predatory dinosaur with even stubbier arms than Tyrannosaurus rex may now hint that a vast desert once existed in the heart of a lost supercontinent, potentially barring this carnivore and its kin from spreading across the entire ancient world, researchers say.

When T. rex and its tyrannosaurid relatives dominated as predators in the Northern Hemisphere in what is now North America and Asia, carnivores known as abelisaurids were the top killers in the Southern Hemisphere on the lost supercontinent of Gondwana, which once was made up of what is now Antarctica, Australia, South America and Africa.

The newfound abelisaurid species, discovered in Patagonia in Argentina, is named Eoabelisaurus mefi, or "dawn Abelisaurus of the Museo Palentológico Egidio Feruglio." Based on the nearly complete skeleton, the carnivore was about 21 feet long and lived about 170 million to 175 million years ago, back when the area was hot and ranged between pronounced dry seasons and extensive rain.

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The finding, detailed online May 23 in the journal Proceedings of the Royal Society B, suggests the abelisaurids, whose origins have remained enigmatic, originated at least 40 million years than before thought. This meant that abelisaurids existed back when all the continents were united in the supercontinent Pangaea. [ See Photos of the New Dinosaur ]

Little arms
Abelisaurids generally resembled tyrannosaurids in appearance, stalking the land on two legs, although their skulls were relatively shorter in length and taller in height, with a shape that hinted they had extremely powerful bites. As squat as the arms of tyrannosaurids were, abelisaurids had even squatter limbs that appeared even less useful — for instance, they typically lacked wrist bones.

"Why these animals had such tiny arms is a good question," said researcher Oliver Rauhut, a paleontologist at the Bavarian State Collection for Paleontology and Geology in Germany. "One part of the answer might be that both had skulls that were adapted for very powerful bites, so these animals obviously relied on 'head hunting' for acquiring prey and didn't need the arms for that."

Rauhut added that tyrannosaurids and abelisaurids had specialized arms, with abelisaurids having an enlarged shoulder girdle, indicating muscle strength, as well as more flexibility of the upper arm. "What they did with these arms is anybody's guess," Rauhut said.

Dinosaur barrier
The fossil was first discovered in 2009 during a large-scale prospecting campaign by researcher Diego Pol at the Egidio Feruglio Paleontological Museum in Argentina in a dry, savannahlike landscape. "Basically everything that grows there has thorns," Rauhut said. Native animals include the lowland llama, a small flightless bird known as the nandu, and armadillos, "but what you see most is actually sheep," Rauhut added.

The arms of Eoabelisaurus are not as tiny as those of later abelisaurids, but they are still unusually small, revealingthat shortening of abelisaurid arms began very early in their evolution. This reduction apparently started with the lower arm — in Eoabelisaurus, the upper forelimb is of normal size, but the lower arm is much shorter in comparison, with a very stunted hand and tiny fingers and claws.

Image: Excavating specimen of the abelelisaurid dinosaur
Oliver Rauhut
Researchers excavating the specimen of the abelelisaurid dinosaur named Eoabelisaurus mefi.

The fact that Eoabelisaurus lived about 175 million years ago suggests abelisaurids could have spread across the whole of Pangaea before it fragmented about 10 million to 15 million years later into Gondwana and Laurasia, the supercontinent once made up of what is now Europe, Asia and North America. Since abelisaurids were apparently exceedingly rare in the Northern Hemisphere, a natural barrier may have prevented their advance northward, researchers suggested.

Growing evidence from climate models and geological data suggests a huge desert in the center of Gondwana might have kept abelisaurids from dispersing to the north. Such a barrier could also explain why other groups of animals were restricted to Gondwana, such as certain mammals and giant plant-eating sauropods, the researchers explained.

The scientists hope to continue investigating the dinosaurs of Patagonia. " Dinosaurs from the Southern Hemisphere are still extremely poorly known, so we can expect to find more surprises," Rauhut told LiveScience.

© 2012 LiveScience.com. All rights reserved.

Explainer: The world's seven deadliest dinosaurs

  • Copyright 1985 Mark Hallett, "Awakening of Hunger"

    Yeah, it's cliche to say Tyrannosaurus rex was deadly. But the tyrant king was likely true to the billing. Its bone-crushing jaws could splinter prey like toothpicks, after all. And the beast was big, up to 40 feet long, 20 feet tall, and may have topped the scales at nearly 16,000 pounds.

    The king walked on two legs over a vast territory in western North America at the end of the Cretaceous, about 65 million years ago. Scientists wonder whether T. rex was more a lumbering scavenger or a quick and agile predator, but dead or alive, its meals were big, meaty and bloody.

    T. rex wasn't the only deadly dino, however. The globe was filled vicious killers. Click the arrows above to see more.

    — John Roach, msnbc.com contributor

  • Family diner

    Demetrios M. Vital

    Family meals for Majungasaurus crenatissimus were often bloody affairs of the grimmest sort: Kin were the main course. The evidence of its cannibalistic ways comes from telltale tooth marks on Majungasaurus bones that match up perfectly with the size and spacing of teeth in its jaws.

    The 20-foot-long dinosaur stalked the plains of Madagascar about 70 million years ago. At that time, the crime-scene investigators said, pickings were often slim. Their data indicate Majungasaurus fed on dried out "dino jerky" from its plant-eating compatriots as well as members of its own species. Cannibalism was likely just as common among dinosaurs as it is among living animals, but the evidence is rare.

  • Brow beater

    Todd Marshall

    Eocarcharia dinops' brow was swollen into a massive band of bone. The menacing head piece may have been used as a battering ram against rivals and to attract potential mates. Its blade-shape teeth were reserved for disabling live prey and severing their body parts.

    The 110-million-year-old beast and its snout-nosed, gut-and-carcass-scavenging relative Kryptops palaios were discovered in Africa's Sahara Desert. The approximately 7-foot-tall and 25-foot-long duo likely teamed up with a third carnivore and feasted on the long-necked plant-eater Nigersaurus.

  • Vicious rocker

    Parsons

    The toothy Masiakasaurus knopfleri likely speared prey with its forward projecting front teeth and then sliced and tore the captives into chewy chunks with its bladelike rears. This type of tooth arrangement is otherwise unknown in predatory dinosaurs.

    Scientists believe the German Shepherd sized beast feasted on fish, lizards, and other critters on the southern supercontinent Gondwana in the Late Cretaceous period, about 65 to 70 million years ago.

    The first part of this dinosaur's name means "vicious lizard" and the second part is derived from the Dire Straits singer and guitarist Mark Knopfler, whose music inspired the discoverers as they toiled on the African island nation of Madagascar.

  • Biggest carnivore?

    Prof. Rodolfo Coria / Ap

    At about 40 feet long and weighing an estimated 6 tons, Mapusaurus roseae was one of the biggest meat-eating dinosaurs to ever stalk the Earth. Bones of several individuals were discovered in one place, suggesting the giants may have hunted in packs that could have toppled perhaps the largest dinosaur that ever lived — a 100-foot-long plant eater called Argentinosaurus.

    Mapusaurus lived about 100 million years ago and was bigger than well known Tyrannosaurus rex and possibly larger than its older cousin, Gigantosaurus. Its teeth were narrow and blade like, made for slicing its prey. The bones were discovered in the Patagonia region of Argentina.

  • Going green

    MWS

    Falcarius utahensis is the living image of a vicious meat eater trying to go vegetarian. Scientists aren't sure if the bird-like relative of Velociraptor had fully kicked its taste for flesh, but its meat-cutting teeth had shrunk to leaf-cutting size and its gut had expanded sufficiently to ferment plants.

    Falcarius walked on two legs and stood about 4.5 feet tall. Head to tail, it was about 13 feet long and wielded sharp, curved, four-inch long claws — perhaps to grab a bite when it fell off the wagon? The dinosaur lived during the Early Cretaceous, about 125 million years ago, in what is today Utah.

  • Plant ripper

    utah.edu

    No plants were safe from Gryposaurus monumentensis, a big boned, duck-billed dinosaur that could have eaten any vegetation it stumbled across. Its massive skull packed more than 300 teeth for slicing up fibrous greens. Hundreds more replacement teeth rested in its jawbone for the call-up to action.

    The dinosaur lived in the Late Cretaceous, about 75 million years ago on the western side of a giant, shallow ocean that split North America at that time. The plant-munching beast may have reached 30 feet long as an adult and had a 3-foot-long head.

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