This article first appeared in the St. Louis Beacon, Feb. 10, 2010 - I was forced to learn to spell archaeopteryx in 1989, when my daughter Nikki came home from first grade at Meremac School reciting "A-R-C-H-A-E-O-P-T-E-R-Y-X." Her class was just starting to learn to spell, and the teacher assigned them that word right off the bat. "If you can spell archaeopteryx," she told them, "you can spell anything." Every kid in that class learned how to spell archaeopteryx, and, in doing so, felt they could learn anything they set their mind to. Good teacher.
Archaeopteryx (pronounced "archie-op-ter-ichs") is the first bird for which we have clear fossil evidence. About the size of a crow, the first fossil was found in a 150 million-year-old limestone quarry in Bavaria in 1861. It had the clawed fingers and long bony tail of a dinosaur, with the wishbone and feathered wings of a bird.
For more than a century people have argued about archaeopteryx. Did archaeopteryx evolve from a dinosaur or from some other reptile? It is difficult for a non-paleontologist to appreciate the heat with which this seemingly dry question has been, and is being, argued.
Boiling more than a century of ferocious argument down to a few lines, the preponderance of evidence favors a dinosaur ancestor. Archaeopteryx is remarkably like a therapod dinosaur called velociraptor. You may remember velociraptors as the scary guys that stalked the kids in the kitchen in the film "Jurassic Park." Like velociraptor, archaeopteryx has an unusual swivel-jointed wrist, a long, very deep shoulder blade, a fused collar bone (familiar as the "wishbone" of Thanksgiving turkeys), and many other shared features.
As in all good scientific fights, evidence hasn't discouraged dispute. Despite a mountain of evidence that birds evolved from dinosaurs, a few scientists I will call the die-hards still refuse to accept this conclusion. Every few months in the widely read journal SCIENCE there's an article by one of the die-hards, arguing the case against the dinosaur-bird link. Its guys like these that make science fun.
What should have been the final nail in the die-hards' coffin, the "smoking gun" proof of a dinosaur-bird direct link, was the discovery in 1996 in China of dinosaurs with feathers. The first of these, called Sinosauropteryx, has no wings, but is covered with a light feather-like fuzz. A dinosaur with a feather coat.
"Not really feathers," object the die-hards, "Just fuzz."
Two weeks ago, researchers sorted all this feather fussing out. Paleontologist Mike Benton and colleagues at the University of Bristol, England, reported that the simple blunt feathers of Sinosauropteryx contain tiny bag-like organelles called melanosomes, each stuffed with either the black pigment melanin (the same pigment that makes you tanned and a crow black), or the reddish-brown pigment pheomelanin (which gives a chestnut color similar to last year's Kentucky Derby winner Mind That Bird).
The presence of melanosomes is a common occurrence in the animal kingdom. They are found within the exterior cells of all the major groups of vertebrates. The discovery of melanosomes by the Bristol group proves beyond dispute that the bristles studding Sinosauropteryx are indeed feathers and not collagen fiber fuzz.
In birds today, the shape and arrangement of melanosomes helps produce the color of bird feathers. Using scanning electron microscopes to examine the surfaces of the dinosaur feathers, the University of Bristol researchers found the Sinosauropteryx melaonsomes were not randomly located along the tail feathers, but rather occurred in broad bands – the dinosaur had alternating orange and white rings down its tail!
In the years since Sinosauropteryx was discovered, another very exciting fossil has come to light from the same Chinese fossil fields. Called Caudipteryx (that's "caw-dip-ter-ichs"), Greek for "tail feathers," the fossil dinosaur has large feathers on its tail and arms. Big feathers, not bristles, with much of the detailed architecture of modern bird feathers. Symmetrical, the feathers could not have been flight feathers, whose leading and trailing edges need to be of different widths to promote lift. But feathers they are, beyond any quibble.
Two of these feathered Caudipteryx dinosaurs were discovered in 1998, and a third beautifully preserved specimen was reported a few years later.
"If it has feathers, it must just be some kind of bird we don't know much about," object the die-hards.
Paleontologists disagree. While Caudipteryx has a handful of bird-like features, including feathers, it has many features of velociraptor dinosaurs, including short arms, serrated teeth, a velociraptor-like pelvis, and a bony bar behind the eye. Paleontologists who have studied the new fossils describe Caudipteryx as sitting on a branch of the dinosaur family tree between Velociraptor and Archaeopteryx.
It seems feathers are not a distinguishing trait of birds. They first evolved among the dinosaurs. Because the arms of Caudipteryx were two short to use as wings, feathers probably didn't evolve for flight. Instead, they probably served as a colorful display to attract mates (as they do in peacocks today), or as insulation (as they do in penguins today). Flight is something that certain kinds of dinosaurs achieved as they evolved longer arms. We call these dinosaurs birds.
'On science'
George B. Johnson's "On Science" column looks at scientific issues and explains them in an accessible manner. There is no dumbing down in Johnson's writing; rather he uses analogy and precise terms to open the world of science to others.
Johnson, Ph.D., professor emeritus of Biology at Washington University, has taught biology and genetics to undergraduates for more than 30 years. Also professor of genetics at Washington University’s School of Medicine, Johnson is a student of population genetics and evolution, renowned for his pioneering studies of genetic variability.
He has authored more than 50 scientific publications and seven texts, including "BIOLOGY" (with botanist Peter Raven), "THE LIVING WORLD" and a widely used high school biology textbook, "HOLT BIOLOGY."
As the founding director of The Living World, the education center at the St Louis Zoo, from 1987 to 1990, he was responsible for developing innovative high-tech exhibits and new educational programs.
Copyright George Johnson