The Rise and Fall of the Dinosaurs: A New History of a Lost World: The Definitive Dinosaur Encyclopedia with Stunning Illustrations, Embark on a Prehistoric Quest!

by Steve Brusatte

There are other methods that can date individual crystals found in sandstones and mudstones, but these are expensive and time-consuming. This means that it’s often difficult to date dinosaurs accurately.

Geography class would have been easy in those days: the supercontinent we call Pangea, and the ocean we call Panthalassa.

And what about the climate? No better way to put it: the earliest dinosaurs lived in a sauna.

Compared to today, the Arctic and Antarctic were balmy, with summer temperatures similar to those of London or San Francisco, and winter temperatures that barely inched below freezing.

The marked temperature differences between north and south caused violent air currents to regularly stream across the equator. When the seasons changed, these currents shifted direction. That kind of thing happens today in some parts of the world, particularly India and Southeast Asia. It’s what drives the monsoons, the alternation of a dry season with a prolonged deluge of rain and nasty storms.

The equatorial region was extremely hot and humid, a tropical hell that would make summer in today’s Amazon seem a trip to Santa’s workshop by comparison. Then there were vast stretches of desert, extending about 30 degrees of latitude on either side of the equator—like the Sahara, only covering a much broader swath of the planet. Temperatures here were well into the hundreds (over 35 degrees Celsius), probably all year long, and the monsoonal rains that pounded other parts of Pangea were absent here, offering little more than a trickle of precipitation. But the monsoons exerted a great impact in the midlatitudes. These areas were slightly cooler but much more wet and humid than the deserts, far more hospitable to life.

The high concentration of carbon dioxide in the Late Triassic started a chain reaction: huge fluctuations in temperature and precipitation, raging wildfires during parts of the year but humid spells in others. Stable plant communities had a difficult time establishing themselves. It was a chaotic, unpredictable, unstable part of Pangea.

In evolutionary biology speak, this is called convergence: different types of creatures resembling each other because of similarities in lifestyle and environment. It’s why birds and bats, which both fly, each have wings. It’s why snakes and worms, which both squirm through underground burrows, are both long, skinny, and legless.

What morphological disparity does is measure diversity based on features of the anatomy. Thinking this way, you can consider birds to be more diverse than jellyfish, because birds have a much more complex body with lots of different parts, whereas jellyfish are just sacs of goo.

The problem boils down to this: as a continent tears, it bleeds lava. It’s nothing more than basic physics. The Earth’s outer crust is pulled apart and thins, decreasing pressure on the deeper parts of the Earth. As pressure lessens, magma from the deeper Earth rises to the surface and erupts through volcanoes. If there is only a little rip in the crust—two small bits of a continent separating from each other, let’s say—then the effects aren’t too bad. You might get a few volcanoes, some lava and ash, some local destruction, and then eventually it stops. That kind of thing is happening in eastern Africa today, and it’s far from catastrophic. But if you’re slashing apart an entire supercontinent, then you approach the realm of apocalypse.

This is exactly what is occurring in eastern Africa today, as Africa is pulling away from the Middle East at the rate of about one centimeter per year. The two landmasses used to be connected about 35 million years ago, but now they are separated by the long and skinny Red Sea, which continues to get wider year by year and will one day turn into an ocean. To the south, on the African mainland, there is a north-south band of basins, each growing wider and deeper with every earthquake that is yanking Africa and Arabia farther apart.