Science / Medicine : FEARSOME DINOSAUR : The Life and Times of ‘Big Al’ : About 150 million years ago, allosaurs ruled the dinosaur world. In what is now Wyoming, scientists found a nearly intact skeleton that should shed new light on this large predator.
Roughly 150 million years ago, a young but huge flesh-eating dinosaur roamed along what was then a river bottom in what is now northern Wyoming. Perhaps drawn by the appealing smell of dying vegetarian dinosaurs nearby, the creature tromped through a stream bed, but then somehow died.
In recent years, the erosion of a creek began to reveal bony bits of its tail. Then, in September, rock-chipping paleontologists arrived and uncovered nearly the entire skeleton of the creature, known scientifically as Allosaurus fragilis.
Twisted around in a death pose--the result of flesh and tendons drying in the prehistoric sun--these grayish bones make up what is probably the oldest, most complete skeleton of a large carnivorous dinosaur ever found. Recently hauled by flatbed truck to a Montana State University laboratory, it may help depict the character of early dinosaurs--how they grew and evolved into later forms--and their environment.
“Despite what we do know about dinosaurs, and it’s not all that much, there are many more pieces of the puzzle we haven’t found,” said Jack Horner, curator of paleontology at MSU’s Museum of the Rockies and a pioneer in deciphering dinosaur lifestyles. “This find is valuable even if it fills in part of one piece, and it’s a great spectacle to see.”
Though there are any number of theories, from meteors to volcanoes, about why they died out, much research today tries to illustrate how dinosaurs lived. No one is sure of their life spans or even what color they were. Still, remains of an ancient kingpin like the allosaur (though it could be male or female, digging crews dubbed this one “Big Al”) may add definition to the picture scientists have of that vibrant world long ago.
What scientists already know is that dinosaurs were probably about the most successful form of advanced life on Earth, ruling for close to 150 million years, compared to the million or so years humans have been around. And though a commercial digging crew found this allosaur only 100 yards from a renowned Wyoming quarry that yielded close to 4,000 dinosaur bones in the 1930s, the modern view of dinosaurs has come far beyond what it was in those days of early fossil finds.
“Coldblooded, sluggish creatures of low metabolism, their habits were analogous to the living salamanders,” Barnum Brown, a famed paleontologist from the American Museum of Natural History in New York, wrote of the lumbering leaf-eaters he dug out of the quarry. He unearthed those from the Wyoming Badlands in a 1934 expedition funded by Sinclair, the oil company with a dinosaur as its logo.
Today, though, it seems likely dinosaurs were not the languid, pea-brained lizards once thought. Instead, remains--from hurried footprints to a preserved nesting colony in Montana--show they might well have been warmblooded like birds (to which they are probably related), probably had a social structure, tended their young, were rather crafty at times and ran quite fast.
Standing more than twice as high as an average human, allosaurs were the dominant North American carnivore of their day--the late Jurassic period, early in the dinosaurs’ reign. They evolved about 80 million years before Tyrannosaurus rex, the biggest, best-known and most fearsome of the predatory dinosaurs. Both, though, had a similar jaw full of teeth--serrated like thumb-size steak knives--and walked on two legs with their tails held high as a balance.
Each discovery of a predatory dinosaur is all the more important, not just because predators themselves are relatively rare but also because predators mirror their environment. In a kind of prehistoric arms race, allosaurs responded to the defensive armament of other dinosaurs, like the protective plates and spiked tail of the stegosaurs, by developing bigger and stronger jaws and more agile limbs through the generations.
Though dwarfed by the big vegetarian dinosaurs with legs as thick as tree trunks, allosaurs were among the first giant flesh-eaters, and an early link in the evolutionary chain leading to Tyrannosaurus rex, the biggest carnivore that has ever lived.
“If you were hanging around the Cretaceous (from 144 million to 66 million years ago, the time of tyrannosaurs), you wouldn’t want to run into a tyrannosaurus; if you were in the Jurassic, you wouldn’t want to see an allosaurus,” offered Pat Leiggi, the Montana State University paleontologist who supervised Big Al’s unburial on the flanks of the Bighorn Mountains. “This was certainly the top dinosaur of its day, which makes it all the more interesting to us--to see why that was.”
Allosaurs have been found before, but only in bits and pieces that paleontologists had to guess at putting together. Doing that with other remains led many museums to leave the wrong head on big brontosaurs until realizing, in the 1970s, that it didn’t fit. This skeleton is more than 90% intact, Leiggi said. As they chiseled away at the sandstone encasing it, diggers hoped that within the changing modern context of dinosaurs, this one may open our narrow window on the ancient reptiles’ lives a little wider.
By measuring the scars where dinosaurs’ muscle were bound to bones, for instance, researchers can get an idea how strong they were: Such work may prove whether allosaurs could sprint in pursuit of prey, as some researchers believe, or whether they used their burly arms to haul down food. Compared to tyrannosaurus, allosaurs wielded bigger forelimbs with three sharp, grasping fingers, suggesting they were more active hunters than scavengers, said paleontologist Brooks Britt of Canada’s Royal Tyrell Museum near Calgary.
There remains debate over whether carnivorous dinosaurs were as fearless as their jaws and picture-book lore suggest. Some scientists think that with herbivorous dinosaurs traveling in herds like the bison of the American West, carnivores may have followed in social packs, like wolves, feeding on the old or sick. That is, after all, how most known predators behave--weeding out the weak and thereby keeping prey populations fit, not just attacking anything available. If that’s the case, it is also likely carnivores like the allosaurs, by effectively strengthening dinosaur populations as a whole through survival of the fittest, contributed to the historic success of their kingdom.
Though allosaurs may have held sway over their dominion, the particular one unearthed in Wyoming has also became the subject of a modern paleontological tug-of-war. Found by a Swiss for-profit fossil digging team, it was seized by the U.S. government, since the team had unknowingly been prospecting on federal land run by the U.S. Bureau of Land Management (BLM).
That renewed questions of whether digging for fossils to sell privately should be permitted in the United States at all (it now is permitted on private land) or whether fossils should be in a special protective realm as they are in many other countries. Since this find revealed “what could have been lost,” Leiggi said, the Society of Vertebrate Paleontologists will discuss this month whether to pursue legislation defining fossil remains as a national resource.
In the meantime, both Montana State University--known for its dinosaur expertise--and the Smithsonian Institution have stepped in and sought to recover the fossil. That contest was settled only when BLM Director Cy Jamison, a Montana native, opted to keep the dinosaur in the West rather than send it to a big eastern museum as has historically happened. Proud local entrepreneurs are now selling hats and T-shirts with Big Al’s bony likeness.
Brushing dust off the allosaur remains with whisk brooms and painting the bones with acrylic to keep them from crumbling, paleontologists look for clues to explain why this dinosaur is where it is. Surrounding rock was deposited long ago by streams, suggesting the allosaur may have died in a flood and been buried by waterborne sand.
Diggers found predatory footprints near some of the herbivorous dinosaur bones. On a multimillion-year time scale, it would be difficult to prove this dinosaur was lured here by the promise of that food, but it is one possibility.
“In a real sense, we’re trying to recreate this scene in the dinosaur’s life,” said Brent Breithaupt, curator of the University of Wyoming’s museum. “We want to know what brought this animal to this spot, and why all the bones stayed together here. It’s extraordinarily rare that nature will preserve this fine a specimen for so long.”
Scientists can tell the allosaur is a juvenile, a teen-ager, since its back vertebrae are not fused together. Such youngsters of any species, but especially predators, are not well known, putting paleontologists in the awkward position of a pediatrician who has only examined adults. By looking at youngsters, Britt said, scientists may be able to tell how fast allosaurs grew and how long they lived. Puppies, for instance, have big feet and heads that suggest how much more their smaller bodies still need to develop before they match.
And that is telling because to grow quickly, animals must keep up a higher metabolism, which is rarely seen in anything but warmblooded creatures. If dinosaurs were warmblooded like humans and other mammals, they probably lived an enthusiastic lifestyle in pursuit of food. Researchers guess, for instance, that Deinonychus, a small predatory dinosaur with a ghastly sickle-shaped talon (its name means “terrible claw”) would have been anything but sluggish as it slashed down and ripped apart its prey.
A crane finally lifted Big Al’s remains, caked with plaster casts, from the pit where they had lain for eons. Gradually, a hazy vision of this allosaur’s world, probably a wide, tropical plain full of palm-like vegetation and distant pines, has emerged from this dusty layer of earth called the Morrison formation--deposited by Jurassic rivers and now exposed in Wyoming, Montana and famed boneyards such as Colorado’s Dinosaur National Monument. At Como Bluff in southeast Wyoming, so many bones tumbled out of the cliffs that two bright but egotistic paleontologists spied on each other’s digs and broke up leftover bones to make them unusable to competitors.
But all the bones, one at a time, are little more than curios, jumbled pieces of a jigsaw puzzle. Only fitted together--as the allosaur’s remains should be soon--can they offer up a clue to the true lives of the tremendous creatures that once ruled this land.
REIGN OF THE DINOSAURS PRESENT CENOZOIC (Beginning 66 Million Years Ago) MESOZOIC (Dinosaurs at their Peak in Mesozoic Era): CRETACEOUS (Beginning 144 Million Yeats Ago) JURASSIC (Beginning 192 Million Years Ago) TRIASSIC (Beginning 230 Million Years Ago)
THE CREATURE Here is a look at the creature recently unearthed in Wyoming: When: Roamed North America about 150 million years ago, in the late Jurassic era. What: An abundant, large predatory dinosaur. Size: About 36 feet long, weighing about 1.5 tons. About twice the height of average human. Shape: Big S-shaped “bulldog” neck on a bulky body. Tail: long and thick. Limbs: Powerful hind limbs with three-toed clawed feet; short three fingered forelimbs with large share claws. Teeth: Serrated blade-like. Feeding Pattern: Probably roamed in packs, like wolves today, preying on vegetarian dinosaurs. SOURCE: The Dinosaur Data Book, Predatory Dinosaurs of the World
