The Jurassic Period








Above: Argentinosaurus huinculensis silhouetted against a Jurassic landscape, with human figure for scale. To the right, the flying pterosaur Quetzalcoatlus northropi.

Named after the Jura mountains of Germany, the Jurassic Period split from the Triassic after another of the "Big Five" extinctions forever wiped conodonts and ammonites from the future history of our planet. The cause remains murky, like its big brother event that ended the Permian. But the dream-like world that emerged would feature animals of stupefying size.

The largest sauropod thus discovered is Argentinosaurus huinculensis -- weighing 70 tons -- as much as 14 large elephants. Yet it had a tiny head with an even tinier brain, constantly nibbling conifer forests to supply its huge fermenting stomachs with low nutrient material that was broken down by tumbling gizzard rocks and bacteria. By modern standards, these were stupid animals. Mindless grazers with a "second brain" near the tail to control legs that always lingered a second or two behind the central nervous system, these creatures were like a first draft of an ecosystem that would mature and sprawl over a leisurely 150 million years with hardly an interruption -- a trend that would reach astonishing extremes.

Nipping at their elbows were massive early predators like Allosaurus. Great marine reptiles also moved back into the ocean, including fishlike ichthyosaurs, with armor-plated eyes the size of soup plates that enabled them to dive to great depths, and long-necked plesiosaurs, ocean analogs of the sauropods, using their snaky necks to snag fish while their massive bodies paddled slowly around shallow water.


The air was invaded by the toothy horse-sized pterosaurs, with crude gliding wings that followed the era's tendency toward giganticism -- eventually reaching the size of passenger airplanes. Even perched on the ground, Quetzalcoatlus would have stood taller than a giraffe.

A hundred million years slipped by, and the Earth appeared to be setting into comfortable middle age, a world with few surprises left. No great event separates the Jurassic from the Cretaceous, allowing us to see the full fruits of uninterrupted evolution.