sexta-feira, 22 de outubro de 2010

Como Construir um Dinossauro - A Extinção não tem que ser para sempre



 Nothing is too wonderful to be true if it be consistent with
the laws of nature, and in such things as these, experiment
is the best test of such consistency.
—Michael Faraday

Let’s suppose you wanted to pick a moment in the history of life and play it over again, backward and forward, like a football play on a highlights DVD, so you could see exactly how it happened. Rewind. Stop. Play. Rewind frame by frame. Stop. Play frame by frame.

Stephen Jay Gould, one of the best-known evolutionary biologists of his time, wrote in Wonderful Life, his book on the weird and wonderful fossils of a rock formation known as the Burgess Shale, that you can’t go home again, evolutionarily, unless you want to risk not being here when you come back. What he was saying was that evolution is a chance business, contingent on many influences and events. You can’t rewind it and run it over and hope to get the same result. The second time through Homo sapiens might not appear. Primates might not appear.

That’s evolution on a grand scale, major trends in the history of life that involved mass extinctions and numerous species jockeying for evolutionary position. We can’t rewind that tape without a planet to toy with. But I’m thinking about a time machine with a somewhat closer focus, an evolutionary microscope that could target, say, the first appearance of feathers on dinosaurs, or the evolution of dinosaurs into birds.

This time machine/microscope could zero in on one body part. For birds we might start small, with a much maligned body part—the tail. We don’t think about tails much, not at the high levels of modern evolutionary biology, but they are more intriguing than you might imagine. They appear and disappear in evolution. They appear and disappear in the growth of a tadpole. Most primates have tails. Humans and great apes are exceptions.

The dinosaurs had tails, some quite remarkable. Birds, the descendants of dinosaurs, now almost universally described by scientists as avian dinosaurs, do not have tails. They have tail feathers but not an extended muscular tail complete with vertebrae and nerves. Some of the first birds had long tails, and some later birds had short tails. But there is no modern bird with a tail.
How did that change occur? Is there a way to re-create that evolutionary change and see how it happened, right down to the molecules involved in directing, or stopping, tail growth?...



INTRODUCTION

HELL CREEK
TIME, SPACE, AND DIGGING TO THE PAST 

IT’S A GIRL!
A PREGNANCY TEST FOR T. R E X 

MOLECULES ARE FOSSILS TOO
BIOLOGICAL SECRETS IN ANCIENT BONES 

DINOSAURS AMONG US
CHICKENS AND OTHER COUSINS OF T. R E X 

WHERE BABIES COME FROM
ANCESTORS IN THE EGG 

WAG THE BIRD
THE SHRINKING BACKBONE

REVERSE EVOLUTION
EXPERIMENTING WITH EXTINCTION 
APPENDIX: CHICKENOSAURUS SKELETON 
BIBLIOGRAPHY 
ACKNOWLEDGMENTS 
INDEX



HOW TO BUILD A DINOSAUR - EXTINCTION DOESN’T HAVE TO BE FOREVER [ Download ]