Fossils of New Species Add to Mystery of Demise of Dinosaurs

Fossils of at least four new species of animals discovered in Wyoming cast doubt on the theory that comets colliding with the Earth killed off some dinosaurs 130 million years ago and all dinosaurs 65 million years later, a Colorado paleontologist said Wednesday.

The new species include a 20-pound herbivorous dinosaur, a bizarre mammal that the researchers have nicknamed a “mutant ninja chipmunk” and a “high-tech” turtle. They flourished after the large dinosaurs that preceded them were exterminated 130 million years ago by an unknown environmental catastrophe, said Robert Bakker of the University of Colorado at Boulder.

Many researchers believe that cometary collisions produced highly acidic rainfall and cold temperatures that led to the dinosaurs’ decline. But discoveries at the new site cast doubt on that proposal because other reptiles and fish, which should have been affected by the cold and acid, proliferated while the dinosaurs died out.

“The mechanism (of extinction) obviously needs to be rethought,” said Bakker, who is considered by many paleontologists to be a maverick in the profession.

It is not widely appreciated that dinosaurs went through two distinct periods of dominance. During the late Jurassic Period, which extended up to 130 million years ago, the largest dinosaurs were well-known varieties such as the long-necked brontosaurus, the spike-backed stegosaurus and the fierce, carnivorous allosaurus.

These species died off at the end of the Jurassic, to be replaced by small dinosaurs that evolved into the iguana-like iguanodons, the dome-headed dinosaurs and the largest land-based predator ever to exist, Tyrannosaurus rex-- all of which were wiped out at the end of the Cretaceous period 65 million years ago.

“This dramatic change in the evolutionary cast of characters (between the Jurassic and Cretaceous) is one of the most profound crises in dinosaur development,” Bakker said. “The new fossils are the remains of animals that lived in a crisis interval during the early Cretaceous period, and this is the first rock layer (containing the fossils) that seems to record just what happened and why.”

That rock layer, known as the Breakfast Bench, lies in Wyoming’s Albany County, near the town of Rock River. Bakker has been studying the site since 1974, but the bones obtained there, he said, “are so small that I misidentified them at first.” It was only when he and his colleagues found an almost complete skeleton of a 20-pound dinosaur now called Drinker nisti “that I realized what we had been getting and the new species kind of jelled.”

The fossil bed indicates that the region was swampy and fern-choked at the end of the Jurassic. Similar conditions prevailed at the end of the Cretaceous and at the end of the Permian period 250 million years ago, when another extinction occurred before dinosaurs existed. Swamps have also been associated with other, smaller extinctions, Bakker said.

“It looks like we have a ‘serial killer’ here that has something to do with swamps,” he said. “We’re not ready for convictions yet, but we certainly have enough evidence for an indictment.” He speculates that the dinosaurs were killed by disease as they moved into new environments in response to climate change.

But, noted geologist Walter Alvarez of UC Berkeley, there is “overwhelming evidence” that a cometary impact did occur at the end of the Cretaceous period. “We may never know precisely what the killing mechanisms were, but it would require a breathtaking coincidence to say that a gigantic impact had nothing to do with a gigantic extinction,” said Alvarez, a long-time proponent of the impact theory of extinction.

Paleobiologist Hans Sues of the Smithsonian Institution’s National Museum of Natural History in Washington called Bakker’s claim about a serial killer “wild,” but noted that Bakker “does have a very interesting new dinosaur and little animals there.”

Bakker has been criticized in the past for making strong claims in the media and for not publishing his results in refereed journals. The current findings were published recently in the Proceedings of the Fourth North American Paleontological Congress, a non-refereed journal. The fact that a paper is unrefereed means that other scientists have not subjected it to critical review.

The fossil strata also show that while large land animals died off, smaller aquatic species and reptiles did not. “If a meteorite hit, it would cause a sudden chill and acid rain that would kill off turtles and frogs right away,” Bakker said. “But the frogs didn’t disappear. Neither did the turtles. In fact, the whole aquatic ecosystem bloomed and did fine. That’s a very powerful clue about what happened.” Bakker is not sure, however, what caused the swamps to form.

The most common dinosaur to be found at Breakfast Bench was the new D . nisti, he said. It was equipped with the most complicated leaf-cutting teeth ever to evolve among dinosaurs. The animal’s large, spreadable hind feet were adapted to walking on soggy ground.

Baby D . nisti specimens, with body and leg bones as small as pigeons’, are among the smallest dinosaurs ever found, Bakker said. “You can put a pile of their bones on a dime.”

Zofiabaatar, a ferocious eight-ounce mammal, has been nicknamed the “mutant ninja chipmunk” by Bakker. The animal apparently killed lizards and other small prey with its mouse-like front teeth, then sliced up the bodies with its long, saw-edged rear teeth.

It was a member of a group of mammals known as multituberculates--primarily insect eaters and herbivores that have no relatives living today. “The mutant ninja chipmunk apparently made an evolutionary hard right turn” to become a carnivore, he said.

Foxraptor was a furry, even smaller animal with a bulldog snout designed for attacking large bugs and small vertebrates. The fourth new species, Uluops, was a “high-tech” turtle boasting a skull architecture far more advanced that its contemporary cousins.

The largest common animal in the Breakfast Bench strata was the “giant crushing-tooth lungfish,” a half-ton predator with huge, flat teeth shaped like mittens for cracking hard-shelled prey.

NEW SPECIES FOUND

Colorado paleontologist Robert Bakker has discovered four new species that date from 130 million years ago. Two--the Foxraptor and the Zofiabaatar--are small but ferocious mammals. One--the Uluops--is a neurologically sophisticated turtle. The fourth--the Drinker--is a 20-pound plant-eating dinosaur. Illustrations: University of Colorado