The Last Days of the Dinosaurs (eBook)

Introduction

Picture yourself in the Cretaceous period. It’s a day like most any other, a sunny afternoon in the Hell Creek of ancient Montana about 66 million years ago. The ground is a bit mushy, a fetid muck saturated from recent rains that caused a nearby floodplain stream to overrun its banks. If you didn’t know any better, you might think you were wading on the edge of a Gulf Coast swamp on a midsummer day. Magnolias and dogwoods shoulder their way into stands of conifers, ferns, and other low-lying plants gently waving in the light breeze drifting over the open ground you now stand upon. But a familiar face soon reminds you that this is a different time.

A Triceratops horridus ambles along the edge of the forest, three-foot-long brow horns slightly swaying to and fro as the pudgy dinosaur shuffles its scaly, ten-ton bulk over the damp earth. The dinosaur is a massive quadruped, seemingly a big, tough-skinned platform meant to support a massive head decorated with a shield-like frill jutting from the back of the skull, a long horn over each eye, a short nose horn, and a parrot-like beak great for snipping vegetation that is ground to messy pulp by the plant-eater’s cheek teeth. The massive herbivore snorts, making some unseen mammal chitter and scramble in alarm somewhere in the shaded depths of the woods. At this time of the day, with the sun still high and temperatures above 80 degrees, there’s barely another dinosaur in sight—the only other “terrible lizards” plainly in view are a couple of birds perched on a gnarled branch peeking out from just inside the shadow of the forest. The avians seem to grin, their tiny insect-snatching teeth jutting from their beaks.

This is where we’ll watch the Age of Dinosaurs come crashing to a fiery close.

In a matter of hours, everything before us will be wiped away. Lush verdure will be replaced with fire. Sunny skies will grow dark with soot. Carpets of vegetation will be reduced to ash. Contorted carcasses, dappled with cracked skin, will soon dot the razed landscape. Tyrannosaurus rex—the tyrant king—will be toppled from their throne, along with every other species of non-avian dinosaur no matter their size, diet, or disposition. After more than 150 million years of shaping the world’s ecosystems and diversifying into an unparalleled saurian menagerie, the terrible lizards will come within a feather’s breadth of total annihilation.

We know the birds survive, and even thrive, in the aftermath of what’s to come. A small flock of avian species will carry on their family’s banner, perched to begin a new chapter of the dinosaurian story that will unfold through tens of millions of years to our modern era. But our favorite dinosaurs in all their toothy, spiked, horned, and clawed glory will vanish in the blink of an eye, leaving behind scraps of skin, feather, and bone that we’ll unearth eons later as the only clues to let us know that such fantastic reptiles ever existed. Through such unlikely and delicate preservation our favorite dinosaurs will become creatures that defy tense—their remains still with us, but stripped of their vitality, simultaneously existing in the present and the past.

The non-avian dinosaurs won’t be the only creatures to be so harshly cut back. The great, batwinged pterosaurs, some with the same stature as a giraffe, will die. Fliers like Quetzalcoatlus, with a wingspan wider than a Cessna and capable of circumnavigating the globe, will disappear just as quickly as the non-avian dinosaurs. In the seas, the quad-paddled, long-necked plesiosaurs and the Komodo dragon cousins called mosasaurs will go extinct, as well as invertebrates like the coil-shelled squid cousins, the ammonites, and flat, reef-building clams bigger than a toilet seat. The diminutive and unprepossessing won’t get a pass either. Even among the surviving families of the Cretaceous world, there will be dramatic losses. Marsupial mammals will almost be wiped out in North America, with lizards, snakes, and birds all suffering their own decimation, too. Creatures of the freshwater rivers and ponds will be among the few to get any sort of reprieve. Crocodiles, strange reptilian crocodile mimics called champsosaurs, fish, turtles, and amphibians will be far more resilient in the face of the impending disaster, their lives spared by literal inches.

We know the ecological murder weapon behind this Cretaceous case study. An asteroid or similar body of space rock some seven miles across slammed into Earth, leaving a geologic wound over fifty miles in diameter. Most species from the Cretaceous disappeared in the aftermath. It’s difficult to stress the point strongly enough. The loss of the dinosaurs was just the tip of the ecological iceberg. Virtually no environment was left untouched by the extinction, an event so severe that the oceans themselves almost reverted to a soup of single-celled organisms.

We are fearfully enraptured with the idea of such terrible devastation. When the impact at the end of the Cretaceous was scientifically confirmed, news of the disaster inspired not one but two blockbuster films about planet-killing asteroids in the summer of 1998. That such a huge rock could kill more than half of Earth’s known species suddenly seemed as obvious as the lethality of a gunshot. Simply knowing the terrible consequences of this disaster has been enough for us to look at the night sky with continued suspicion. If it happened before, it may happen again. NASA keeps an eye on the sky through their Sentry program, hoping to identify threatening asteroids and comets before they get too near.

But we often forget the unusual nature of the K-Pg crisis. Experts have often spoken of the calamity as part of the Big Five—a quintet of mass extinctions that have radically altered life’s history. The first extinction crisis, between 455 and 430 million years ago, reshaped the oceans, erasing entire families of archaic invertebrate weirdos and allowing fish to thrive. Rapid global cooling and plummeting sea levels killed about 85 percent of known marine species, reshuffling the evolutionary deck. The second event, spanning 376 to 360 million years ago, shook life up once more. Precisely what caused the disaster is unknown—a drop in ocean oxygen levels is suspected—but the sudden change killed about half of known creatures, reducing the diversity among organisms like trilobites and corals that formed the basis of ancient reefs.

Worse still was the third, peaking about 252 million years ago. This was the Great Dying, fueled by incomprehensibly violent and sustained volcanic activity that wiped out about 70 percent of known species on both land and sea through climate and atmospheric changes. Our protomammal ancestors, who had held sway in terrestrial ecosystems, were almost entirely extinguished. Their downfall is what allowed reptiles, including dinosaurs, to stage their evolutionary coup. Following that, about 201 million years ago, another disaster killed off a great number of the crocodile relatives that ruled the land and gave dinosaurs their shot at dominance. Once again, intense eruptions were to blame. Greenhouse gases belched into the atmosphere, spurring a burst of global warming followed by intense global cooling. Atmospheric oxygen levels dropped, the seas became more acidic, and the drastic shifts between too hot and too cold were too much for many species to cope with.

But none of these catastrophes were quite like the extinction event that ended the Mesozoic. These previous apocalypses took place over hundreds of thousands or even millions of years, with phenomena like intense volcanic activity and climate change creating grinding, protracted transformations that shifted the makeup of life on Earth over long time spans. The causes of death were also highly variable—ocean acidification prevented shell-building creatures from constructing their calcium carbonate homes, for example, while decreased atmospheric oxygen might have slowly choked terrestrial organisms. What happened at the close of the Cretaceous, however, had global reach. And it happened fast.

The happenstances that triggered the Late Cretaceous extinction culminated in one terrible instant, a rare sliver of time that we can pinpoint as the very moment that life would never be the same. Before the strike, thousands of species flourished on every continent. There were so many varieties of dinosaurs and assorted other creatures that paleontologists are still clocking overtime to find them all, with new toothy, sharp-clawed wonders being named every year. Experts even expect that there were scores of species we’ll never know as they lived in places where the circumstances of deposition and sedimentation did not allow them to be preserved, such as dinosaurs that lived in the mountains or other environments that were eroded rather than laid down as layers in stone. Mesozoic life was at its peak. Then, almost overnight, the dinosaurs were all but extinct and the planet’s ecosystems were in disarray. This was the worst single day in the history of life on Earth, followed by tens of thousands of years of struggle for the survivors.

Our view of the K-Pg extinction has been hard-won. In fact, the task has involved overcoming our greatest weakness—human hubris. When the famously cantankerous British anatomist Richard Owen coined the name “Dinosauria” in 1842, the great reptiles weren’t all that much of a mystery. At the time, only three were known to scientists and the scaly trio seemed to mark part of life’s expected...