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Jack Dann and Gardner Dozois

For 140 million years, the world was ruled by monsters.

Monsters covered with horns and spikes and crests and impenetrable armor, monsters fleet of foot with great snapping jaws and rows of deadly, razor teeth like sharks', monsters that soared and glided in the prehistoric skies like great multi-hued dragons and swam like seaserpents in the cold depths of the oceans.

Monsters that still inhabit our nightmares. (And may still share the world with us.)

Monsters that fascinate us.


If you grew up in the 1950s or 1960s, you were probably taught to think of dinosaurs as immense, lumbering, stupid, cold-blooded beasts who spent their days submerged up to the neck in deep water (to help support their vast weight) or perhaps wallowing ponderously through some tropic swamp. There was a smug, self-congratulatory air to this vision; dinosaurs had died out because they were too stupid and inflexible, unable to adapt to changing conditions—unlike we clever primates. The term "dinosaur" is sometimes still used in this fashion today, applied to outmoded, obsolescent institutions or to people who are unable to keep up with changing times in their professions, and there is still a mammalian smugness to the use. As if we survived—or, at least, our distant ancestors did—on the basis of brains, skill, and pluck, while the dim-witted, pea-brained titans couldn't cut it; as if we had outcompeted the dinosaurs, as if we drove them from Earth.

Nothing could be further from the truth. As Adrian J. Desmond has said, "Mammals were in existence as early as the latest Triassic, 190 million years ago, yet for the first one hundred and twenty million years of their existence, from the end of the Triassic to the late Cretaceous, they were a suppressed race, unable throughout that span of time to produce any carnivore larger than cat-size or herbivore larger than rat-size . . . Dinosaurs were the masters of that world, creatures so efficient in physiology and locomotion that they snatched the world from the mammals' grasp and monopolized it for 120 million years."

It's true that many dinosaurs were immense—the "Ultrasaurus," for instance, which is believed to have weighed in at around seventy tons and to have stood some fifty feet tall, may have been the largest land animal ever to exist. And it's true that many dinosaurs were relatively stupid—the vast Brontosaurus (now known instead as "Apatasaurus" to modern paleontologists), for instance, had a brain weighing only 1/100,000 of its body weight. But these were only some of the dinosaurs. With mind-boggling diversity, dinosaurs successfully adapted to—and filled—almost every ecological niche, except for the niche of the ultrasmall, mouse-sized, which was the refuge retreated into by the mammals for the next 120 million years. Says Desmond, "During their [the dinosaurs'] sojourn as rulers of the earth they produced an array of forms to fill the niches now occupied by mammals and birds as dissimilar as elephants, tigers and ostriches." There were some dinosaurs such as Echinodon and Compsognathus Iongipes that were the size of chickens. There were some that were graceful and very fleet of foot. And while some dinosaurs were pretty dumb, some of the late Cretaceous dromaeosaurids like Deinonychus and Saurornithoides were relatively intelligent, with big brains, binocular vision, and grasping fingers with an opposable thumb; dinosaurs that, in Desmond's words, "were separated from other dinosaurs by a gulf comparable to that dividing men from cows."

The debate about whether or not dinosaurs were hot-blooded (first raised by Robert T. Bakker and others in the early 1970s) continues to rage, and will probably be a matter of controversy in scientific circles for decades. Still, whatever side of this controversy one favors, our picture of dinosaurian life has changed considerably from the vision of dim-witted swamp-wallowers prevalent in the 1950s. As Silva J. Czerkas and Everett C. Olson have said, "Pound for pound, most giant dinosaurs were stronger, faster, and more maneuverable than the rhinos and elephants of today." It is now widely accepted that some dinosaurs traveled in herds, with social organization similar to that of herd-animals today, and even the biggest of the plant-eaters are now often thought of as forest-dwellers who filled a niche more like that filled today by elephants or giraffes, than swamp-wallowers. Some other dinosaurs, like some varieties of "duckbilled" hadrosaurs, are known to have nested in large colonies or "hatcheries" as some sea-birds do today, and are believed to have actually reared their young once hatched, rather than just leaving the unhatched eggs to their fate, as most turtles do. It has even been suggested that modern birds are the direct descendants of dinosaurs, so that, in a sense, dinosaurs did not really become extinct after all—that, instead, you see living representatives of the dinosaurs every time you go to the park. You may even have fed bread crumbs to them.

If this is true, however—and it is still highly controversial—then birds are the only remaining dinosaur descendants. Because 65 million years ago, all other dinosaurs suddenly and mysteriously disappeared from the land and the sea and the sky. Dead. All of them, dead—in a span of time that has been variously figured as a million years, a few thousand years, or even a few days. Extinct.

What killed the dinosaurs?

This has been one of the greatest mysteries of science for decades, and there are almost as many theories as there are theorists. For years, a leading theory was that a nearby supernova had blasted Earth with a deadly burst of hard radiation. Other favorites were theories of global drought (remember those dinosaurs in Fantasia, staggering through the desert dying of thirst?), or a worsening of climate, so that they perished from the cold (although there is some new evidence suggesting that some of them already lived in areas with a climate cold enough to form frost and freeze lakes). Worldwide periods of intense volcanic activity have been blamed, as has acid rain. One theory suggested that sneaky little mammals had slunk across the forest floor and eaten the dinosaurs' eggs. There's a theory that attributes the demise of the dinosaurs to a change of diet caused by the spread of flowering plants; another that says the dinosaurs were killed by alkaloid poisoning caused by eating flowering plants; another that says they died of hay fever caused by the spread of flowering plants; and even a theory that the dinosaurs died of constipation when a certain flowering plant with laxative properties became extinct.

The latest favorite, first suggested in 1979 by Dr. Luis de Alverez, is that a huge asteroid had struck Earth's surface, creating monstrous earthquakes, immense tsunamis, global wildfires, and, far worse, smothering clouds of rock-dust, smoke, dirt, and vaporized water that would stretch up into the stratosphere, blotting out the sun and bringing about a scenario similar to that of a "Nuclear Winter": no sunlight, a catastrophic global drop in temperature, and the death of most plant life, including the all-important plankton in the ocean, the basis of the food chain.

This theory was widely accepted through the 1980s. But detractors have begun to pop up, and it is now under attack again. The truth is, none of the theories seem to adequately explain all of the intricate details of the Great Cretaceous Extinction. You might as well suggest, as Clifford D. Simak once did, that hungry aliens ate the dinosaurs, or suggest, as Isaac Asimov once did, that those intelligent and rapacious little dinosaurs we mentioned, Sauronithoides and his ilk, had developed the gun and hunted their larger and dumber relatives to extinction before inventing war and turning on each other.

It is interesting to speculate about what the world would be like today if the dinosaurs hadn't become extinct. Professor Carl Sagan of Cornell University has written: "If it had not been for the extinction of the dinosaurs, would the dominant lifeform on earth today be descendants of Sauronithoides, writing and reading books, speculating on what would have happened had the mammals prevailed?"

And would the title of this book then have been . . . Mam-mals!?

Go know. In the meantime, be glad things have turned out the way they have, and read on.

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