Image: Majungasaurus
Sara Burch and Matthew Carrano
A re-creation of Majungasaurus crenatissimus suggests that the dinosaur could not even pick up anything with its forearms.
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updated 1/11/2012 3:40:55 PM ET 2012-01-11T20:40:55

With its blade-like teeth and formidable claws, Majungasaurus crenatissimus was one of the world’s most fearsome predators, but new research reveals that it also possessed some of the animal kingdom's smallest and most peculiar arms.

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The giant, cannibalistic dinosaur had such disproportionate arms that it could not have grasped anything or even scratched its own face, according to a new study published in the Journal of Vertebrate Paleontology.

Tyrannosaurus rex and other well known predatory dinosaurs also had reduced forelimbs. While Majungasaurus, which lived 66 million years ago in Madagascar, was not a close T. rex relative, some lifestyle factors might have caused them to evolve certain similarities.

"The evolution of short arms in predatory dinosaurs remains a mystery, but fossils like this are an important clue in understanding the process," co-author Matthew Carrano, a paleobiologist at the Smithsonian Institution, told Discovery News.

"Only by discovering the stops leading from 'normal' longer arms in the ancestral forms, to the short and bizarre ones in Majungasaurus and its close relatives, can we hope to explain the evolutionary sequence and its causes."

Carrano and co-author Sara Burch of Stony Brook University analyzed the arm and associated fossils for a new specimen of the Late Cretaceous dinosaur. They concluded that the arm proportions "are unlike anything we see in other theropods."

The forearm bones are only a quarter of the length of the upper arm bones, but would have been thick and muscular. The wrist bones, however, aren't even ossified, and the stubby fingers probably lacked claws.

"The bones of the hand are so small that the fingers may not have even been separated from each other, which means the hand could have been almost paddle-like," Burch told Discovery News.

The result was an arm that was part Popeye and part Barbie. The researchers have no idea what function the arms served.

The forelimbs might have just been stuck at a transitional point in their evolution. If non-avian dinosaurs did not all bite the dust at the end of the Cretaceous, Majungasaurus might have evolved into an enormous ostrich-like animal without arms, but with very strong legs.

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“It is possible that with such large heads full of teeth, some large predatory dinosaurs no longer needed to use their forelimbs to aid in capturing prey, so the forelimbs became smaller as they lost this function,” Burch explained.

During its lifetime, Majungasaurus was about 21 feet long and had a muscular neck, legs and tail. It held the distinction of being the top predator in its territory. Based on fossils bearing its tooth marks, Majungasaurus feasted on enormous long-necked sauropods and didn’t shy away from biting into members of its own species.

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Jonah Choiniere, a postdoctoral fellow at the American Museum of Natural History, said he’s very interested "that this weird arm anatomy is showing up in dinosaurs in Madagascar as well as South America. This shows that whatever the use of the arms, the animals were widespread and successful."

Kristi Curry Rogers, an assistant professor in the biology and geology departments at Macalester College, said the new discovery sheds light on the "highly variable, and sometimes bizarre, anatomy of theropod dinosaurs."

"The tiny hands and unossified wrist bones of this new specimen introduce questions about how these hands and arms evolved and what they were used for," she told Discovery News.

She added, "It is especially interesting that Majungasaurus appears to lack claws — that’s not quite in line with the usual theropod suspects known for their fearsome teeth and claws, and it begs the question of what these strange dinosaurs were doing with their peculiar little hands."

© 2012 Discovery Channel

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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