In the world of paleontology, new discoveries are surfacing so quickly and dramatically these days that fierce old Tyrannosaurus rex soon may be not much more than a 98-pound weakling of the meat-eating dinosaur set.
Last week two Argentine paleontologists announced the discovery of bones of a mammoth creature they dubbed Giganotosaurus (pronounced GHEE-gah-no-toe-sor-us). Stretching as much as 50 feet in length and weighing about 14,000 pounds, it almost dwarfs the remains of the largest T. rex ever found, a five-ton behomoth in Texas.
Nonetheless, as the new heavyweight champion of carnivorous lizards, Giganotosaurus may not remain as the champion for long.
“I have a feeling this guy is going to be dethroned soon enough,” said a laughing Paul Sereno this week, after the Giganotosaurus’ discovery was announced in Nature magazine.
Sereno, the University of Chicago’s world-renowned paleontologist, well knows the details of the find. He has been hunting dinosaur bones in Argentina himself for many years. Long before Argentine paleontologists announced the discovery of Giganotosaurus, they invited Sereno to assess the significance of the find. He was impressed.
Nonetheless, a paleontological discovery like Giganotosaurus, a once-in-a-lifetime event just a generation ago, is nowadays often a brief prelude to even bigger discoveries.
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Sereno, in fact, is one of the new movers and shakers in paleontology who has been speeding up the rate of discovery. He has been finding bones where nobody has looked before and leading the science into new lines of inquiry. And this week, Sereno was intriguingly coy in the wake of the announced discovery of Giganotosaurus.
As for a new discovery that might dwarf Giganotosaurus, he refused to elaborate, except to suggest that somebody is preparing to reveal “next year” the remains of an even-more monstrous meat-eating dinosaur. Sereno wouldn’t say if he or one of his colleagues is that somebody.
Although paleontologists haven’t been aided much by new, sophisticated technology, they have been helped by increased public interest in dinosaurs. That has resulted in more financial support, which, in turn, has meant that more bone-hunting expeditions are now being launched to more places in the world than at any time in history.
There has been a virtual explosion in dinosaur discovery and knowledge. Thirty years ago, there were 250 known dinosaur species; today, there are about 500.
Sereno has been a major source of new dinosaur finds and theories for more than a decade, snooping through America, Africa, Asia and Argentina.
Still, he is clearly impressed with the Giganotosaurus discovery in 1993 by an amateur Argentine paleontologist in the badlands of Patagonia.
“This thing was a monster,” said Sereno, who was invited by Argentine colleagues to the site to examine its fossilized bones. “The people down there believe it was 41 or 42 feet long, but I think they are too conservative. I would guess it was more like 45 or 50 feet long.”
The biggest T. rex was about 40 feet long. However, Sereno observed that trying to guess how large any individual of any dinosaur species could grow is a tricky proposition.
“Individual dinosaurs never stopped growing in their life span,” he said. “They were reptiles, and reptiles don’t have determinate growth limits like mammals do. They continue to grow (though slowly) until they die, while mammalian growth is more peculiar. We (mammals) grow in one big surge to a certain size, and then we stop.
“So we have to collect the remains of a lot of individuals in any given dinosaur species before we can comfortably say what its average adult size was and what its maximum size might have been.”
It’s not easy to collect a lot of individuals. The bones of very few of the uncountable millions of dinosaurs that populated Earth for 165 million years were preserved by nature, and a tiny fraction of those have been found by humans thus far.
Only five fairly complete T. rex skeletons have been found. The species we have the most complete skeletal record of is the 150-million-year-old Allosaurus, for which there are about 60 fairly complete skeletons.
Giganotosaurus’ discovery, Sereno said, will help to fill huge gaps of knowledge of how dinosaurs evolved during their long-running reign over life on Earth.
The first dinosaurs appeared some 230 million years ago, when all the present-day continents were clumped together in one super continent that scientists call Pangea. By the time the dinosaurs disappeared 65 million years ago, the continents had separated.
What makes Giganotosaurus intriguing, Sereno said, is that it evolved about 100 million years ago, when South America was an island continent, as Australia is today.
The land bridge at Panama connecting South and North America hadn’t formed yet.
That means Giganotosaurus and Tyrannosaurus Rex, a North American native that first appeared about 70 million years ago, evolved differently.
Still, T. rex, Giganotosaurus, Allosaurus and other big dinosaur carnivores, known as theropods, all shared some striking physical similarities. All had huge, powerful jaws and short arms, and they walked on strong rear legs, carrying their bodies parallel to the ground.
All lived in temperate climates on savanna-like plains and preyed on plant-eating dinosaurs. They were partial, apparently, to filling their bellies with the flesh of the gigantic, plant-eating sauropods, such as Brachiosaurus and Diplodocus, that, at up to 100 feet in length, were the biggest land animals that ever lived.
“To dinosaur scientists,” said Sereno, “with this (Giganotosaurus) discovery we are seeing basically what was evolving in South America as other things were evolving in North America.”
He said, however, the theropods undoubtedly had a common ancestor that emerged early on in Pangea, when any given dinosaur species could spread by land migration to every corner of the Earth.
Sereno is no stranger to dinosaur-prospecting in Argentina. He has been going there for years, digging bones in a desert 500 miles north of the site of the Giganotosaurus discovery.
“I’ve been looking for the earliest dinosaurs for a number of years,” he said, “those from the first era 230 million years ago. There are some great rock formations in Argentina to look for those earliest ones.”
In fact, he found two very early carnivorous species in the Argentine desert that date to 227.8 million years ago, among the oldest dinosaur bones ever found. One, called Herrerasaurus, was a nearly complete skeleton of a 300-pounder with a serpent-like hinged jaw that enabled it to swallow big chunks of flesh.
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The other, named Eoraptor by Sereno, was a two-legged, bird-like creature that is the most primitive dinosaur known so far to paleontology. About three feet long and weighing 25 pounds, it was one of the smallest meat-eating dinosaurs.
Sereno believes it is one of nature’s earlier versions of the giant carnivores that came millions and tens of millions of years later, a common ancestor to Giganotosaurus and T. rex.
Argentina has become a prime arena for paleontologists following the trail of such dinosaur evolution, he said.
“It’s quite amazing, if you think about it,” he said. “You’ve got one of the smallest, most primitive dinosaurs and the largest (meat-eating) dinosaurs from the same country.”