Skip to main content

View Diary: Camel Purée (198 comments)

Comment Preferences

  •  Why dinosaurs won once, and almost won twice (30+ / 0-)

    For so long, we thought of dinosaurs as lumbering, stupid, overgrown lizards, whose demise at the hands of smart little mammals was foreordained. Even after finally facing up to dinosaurs perhaps being warm blooded, we still clung to the idea that they were scaly, dumb brutes.

    Thing is, mammals developed at the same time as the dinosaurs, and dinosaurs kicked their butt in the ecological marketplace, and kept kicking butt for over 180 million years. So how did that happen?

    At the end of the Permian, the atmosphere of Earth went sour. The cause was probably the "Siberian Traps." Imagine the biggest volcanic eruption you've ever heard of. Now imagine it going on over thousands of square miles. Imagine it lasting for a million years. You're probably still underestimating. The result was a plunge in the oxygen levels that was like taking the whole planet to the height of the Himalayans. The ozone layer was burned away, allowing radiation to sleet to the ground unimpeded. Not just animals died, but plants. Temperatures rose under a blanket of greenhouse gases, turning great swaths of the planet into scorching red deserts that probably looked like the plains of Mars -- only scattered with bones. It was hell.

    Dinosaurs started their rise in these conditions. They did it because before things went bad their ancestors had started development of a system that would give them an incredible edge. Dinosaurs, and their modern representatives the birds, have "pneumaticized bones." That is, many of the large bones in their body are not solid, but constructed of relatively thin shells that are filled with elegant trusses, braces, and a lot of open space. It was long recognized that this system made the bones of these animals lighter without sacrificing strength. It took longer to recognize that these bones aren't just light -- they're also part of the animal's lungs.

    Dinosaurs evolved a system of air sacs that extended into these bones, greatly expanding the area of exchanging gases. They could extract far more oxygen from the air than their competitors. When oxygen levels plummeted, dinosaurs thrived in conditions that were deadly for others. When oxygen levels rose again, dinosaurs rose with them, obtaining an incredible reach of size and diversity.

    The dinosaur metabolism wasn't that of sluggish lizards, it was that of highly active birds. That they reached sizes unmatched by any other land mammal is a measure of tens of millions of years of favorable environment -- and a measure of how much better the dinosaur system was than that of the therapsids came before and after.

    So it shouldn't be a surprise that after the Cretaceous, the first creatures to rise to large size again and dominate the landscape were... dinosaurs. This time in the form of birds. For millions of years, Earth was the planet where birds ate the ancestors of horses -- and probably of humans. Fortunately for us mammals, the dinosaurs that made it past the K-T boundary were limited by the changes they'd already gone through. Birds had surrendered their front limbs to create wings, and while they could drop those wings and take up a ground-based life style, they couldn't readily re-grow limbs (evolution isn't reversible in that way). Birds were just a shadow of the full range of dinosaurian diversity, but they almost pulled it off for a second act. It took millions of years for mammals to displace birds as the top predators of the new age.

    Dinosaurs weren't worse than mammals. They were cursed by success. When disaster struck, they were mostly large creatures with large requirements, unable to make it past the gate when that carnival sign went up.

    But I'm not turning my back on birds. Those guys might be plotting revenge.

Subscribe or Donate to support Daily Kos.

Click here for the mobile view of the site