Guess who's coming to dinner?

Would you believe that the turkey you'll gobble up on Thanksgiving Day is a close relative of the dinosaurs? Paleontologists (scientists who study the evolution of dinosaurs) have found three new pieces of evidence that they say suggest a connection between the birds we know today and dinosaurs that roamed the earth 100 million years ago. Other scientists say no way. Read the evidence and see what you think.

DIGGING FOR CLUES

In hopes of digging up evidence to prove their dino-bird theory, a team of paleontologists from the American Museum of Natural History in New York City went on a dino dig in 1992. The scientists knew that land that has been undisturbed for long periods of time--such as deserts, beaches, or quarries--is usually the best place to find fossils, signs of ancient life (see "We dig science," p. 20). So they chose Mongolia's Gobi Desert, in eastern Asia, as their hunting ground.

We dig science

Teens find that fossils don't just come in dinosaur shapes and sizes.

Ten teens spent three weeks hunting for fossils in central Oregon last summer. Working with scientists from the Oregon Museum of Science and Industry (OMS), the teens found ancient mammal bones.

Central Oregon is a good place to find mammal fossils, says geologist Eric Bestland. Some 34 million years ago, the conditions for fossilization--a quick burial by sediments, slow and steady bombardment by heat and pressure, and a mineral takeover of body tissues--were just right there.

First, active volcanoes erupted in the region, burying animals in ash. The ash, acting like mud, sand, and other sediments, sealed off the animals' bones from the decomposing effects of oxygen and bacteria. As more ash piled up, the accumulating pressure squeezed gases and liquids out of their bodies.

Then, minerals in the soil seeped into tiny holes in the bones. This process of mineral replacement, called petrification, makes the bones strong and rocklike. That's why fossils that formed before humans lived are still here for scientists--and teens--to discover.

Erin Sundermier, 16, of Salem, Oregon, uncovered a fossilized "mouse deer," or hypertragulid, a jungle dweller. Zachary Taggart, 16, of South Wales, New York, found a piglike deer, or oreodont, adapted for roaming grasslands.

The ages of these 30- to 40-million-year-old fossils suggest that Oregon's climate cooled about that time, destroying the jungle, and killing off many of the hypertragulids. When grasslands grew in the jungle's place, the oreodonts prospered.

The teens' fossil finds are now part of a study of Oregon's ancient climate change.

To find out more about teen fossil digs, write:

Dr. Jeffry Gottfried

OMSI 

1945 S.E. Water Ave.

Portland, OR 97214-3354

While plowing through the Gobi, the scientists unearthed some clues: various bones that had been preserved for millions of years. Fossils like these often help solve mysteries of evolution--the development or change of life-forms over long periods of time. "We hoped to find specimens that would help us find out about the origin of birds," says Martin Norell, one of the paleontologists on the Gobi dig.

After several months of digging, the fossil detectives took their finds back to the museum for close inspection. The bones reminded them of specimens collected during earlier digs, particularly an odd "dinosaur" called Mononychus.

When the first specimen of Mononychus was found in 1927, Norrell says "no one did anything with it, because no one knew what it was." Even after another Mononychus specimen was found in Mongolia in 1987, scientists were perplexed: The bones of these Mononychus specimens, and those of the most recent find, looked like they belonged to two different kinds of creatures.

Some features, such as the strong teeth, long bony tail, and short forelimbs, were very dinolike, says Norell. But others--the skull, fused wristbones, and long, hollow leg bones--were more birdlike.

In addition, the most recent Mononychus fossil had a feature not apparent in either of the earlier specimens: a protruding ridge, or keel, on its breastbone--very much like those found in today's flying birds. In these modern-day creatures, the keel is where wingflapping muscles attach.

"We looked at the original specimens," says Norell, "and compared them with our own," and came to a startling conclusion: Mononychus wasn't a dinosaur at all. It was probably a transitional species--a life-form that evolved sometime between dinosaurs and birds, says paleontologist Luis Chiappe, who was also on the Gobi dig.

SUPPORTING EVIDENCE

At the same time the Gobi group was digging up Mononychus bones, another group of scientists was disovering some interesting things about the most primitive flying bird, Archaeopteryx, which lived 147 million years ago. Some of Archaeopteryx's features didn't fit its birdlike reputation, explains Luis Jacobs, a paleontologist at Southern Methodist University in Texas. For example, the creature had a long bony tail, three-finger claws, and teeth like those found in theropod dinosaurs--two-footed beasts, like Tyranosaurus rex and Velociraptor. Archaeopteryx's hips, ankles, and shoulder bones were also similar to theropods'.

Many paleontologists have long believed that theropods were ancestors to modern birds. The smaller theropods, says Jacobs, probably developed and passed on the traits--such as wings and feathers--that enabled their descendants to fly.

If you still don't believe there's a connection between your turkey and T. rex, here's one more piece of evidence. Claudia Baretto, a paleontologist at the University of Wisconsin, recently compared the bone cells of four different critters. "I compared the cells of a young dinosaur to the cells of a lizard, a chicken, and a dog," says Baretto. Specifically, she looked at cells in the growth plates of their leg bones.

After examining the cells under a microscope, Baretto found that the shape and paterns of the cells in the dinosaur's growth plates "matched" the chicken's.

"Whenever two animals share material that is identical," says Baretto, "you can conclude that they [are related]."

THE VERDICT?

Other scientists, particularly some ornithologists (bird scientists), aren't convinced. "The problem," says Alan Feduccia, an ornithologist at the University of North Carolina, "is that the evidence is so scant." Just because specimens like Mononychus have a few birdlike characteristics, says Feduccia, doesn't mean they're birds. Some of Mononychus's features, he says, such as its splintlike fibula (leg bone), are similar to a rabbit's. But that doesn't mean rabbits are descendants of the dinosaurs.

Other scientists agree. Larry Martin, an ornithologist at the University of Kansas, focuses on the differences between the bird and dino specimens more than the similarities. Even if Mononychus has a few birdlike features, says Martin, they're not exact matches. "Show me something that looks the same as a bird's structure," says Martin, "and maybe I'll be convinced."

Martin and other ornithologists believe that birds descended from reptiles--four-legged vertebrates with thick, scaly, waterproof skin. That's the traditional theory among ornithologists. Martin suggests that some small tree-dwelling reptiles that lived 135 million years before the dinosaurs developed wings and, eventually, the ability to fly.

Could it be that dinosaurs and birds both evolved from reptiles? Well, says Martin, dinosaurs and birds could have a common reptilian ancestor. That would explain why birds and dinos share some traits. But that's just another guess. One thing's for sure: The scientists still have a lot of digging to do.

QUIZ

Can you ID a dino?

You may think picking a dinosaur out of a crowd is a cinch. But not every large extinct animal was a dinosaur. Take our quiz to test your dino smarts.

Check out the "snapshots" on this page.

Mark the box on each with a "D" for the ones you think are dinosaurs and "ND" for the non-dinosaurs. Need some help? Run the following tests to determine which creature(s) is/are the real thing.

1. Did the animal live during the Mesozoic Era--between 65 million and 235 million years ago? If it did, go to question 2. If not, stop here--the creature is not a dinosaur.

2. Did the animal hold its body completely off the ground--with two or four legs directly beneath it like a chicken or a dog? If it did, go to question 3. If its belly skimmed the ground like a lizard, you have a non-dinosaur.

3. Did it have flippers or wings? If it did, it's not a dinosaur. Dinosaurs didn't swim or fly. But if the critter walked on land, and you've answered yes to questions 1 and 2, you've finally ID'd a true dinosaur.

Compare answers with your friends. Solutions are in the Teacher's Edition.

To find out more about dinos and other critters in this article, join:

The Dinosaur Society 200 Carleton Ave.

East Islip, NY 11730 1-800-DINO-DON