Survival in the first hours of the Cenozoic (2004) [pdf] | Hacker News Reader

Survival in the first hours of the Cenozoic (2004) [pdf]

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53 pointsmr_toad11 comments

> "The intense IR radiation would have originated from the entire sky. Darkness would have been eliminated worldwide for several hours and shadows curtailed. Shadowing effects would have been restricted to a direct proportion of the fraction of the sky blocked by a massive object. An organism at the foot of a lengthy vertical cliff, for example, would have been spared radiation from just under half the sky. It would not have been sufficient to shelter in a gully, under an isolated tree, or even under a sparsely forested canopy. Life confined to Earth’s surface would have perished well before incineration."

‘‘No one has yet been able to explain under any theory why the crocodiles and turtles survived and the dinosaurs did not.’’

Sure they have. Crocodiles are cold-blooded; they are known to be able to estivate for months without food, waiting for better conditions. Birds and contemporary mammals are small; they can hide, and survive on small scraps. Dinosaurs were both big and warm blooded; the resulting metabolic demand is fatal in hard times.

Not saying the authors aren't right about being able to find shelter against heat pulse also being a factor, of course. But it's not the only explanation.

The cold v. warm blood thing is far more complex. For instance, warm blooded animals can handle slight changes in temperature better than the cold blooded. A wolf's reproductive cycle may be tied to the weather, but a degree or two either way won't really impact the development of its live young. But a degree or two for a croc egg and it might not survive. Or all the crocs one year are male because egg temperature can impact sex selection. If a meteor causes havoc with the climate, that warm blood under some warm fur could be a real advantage.

Oh, to clarify, when I talk about that, I'm not talking about temperature tolerance - that's really more of a secondary byproduct - but metabolic demands. A warm-blooded (i.e. fast metabolism) animal needs an order of magnitude more food than a cold-blooded (slow metabolism) animal.

From what I've read, dinosaurs were not warm-blooded due to their fast metabolism (endothermic) but due to their size and associated heat capacity (homeothermic). That would have made them relatively less susceptible to starvation than present-day mammals, but given their size, they would still require plenty of food.

The big ones. Most were not the movie giants and so were probably much more coldish blooded. It is all a bit of an oversimplification. Some big fish (white sharks) can have internal temperatures a few degrees above water temp. There are all sorts of middle grounds between warm and cold blood.

That too is more complex. An animal like a bear does need more calories, but being warm blooded allows it a greater endurance. A bear can travel further to find food. A bear can access calories over a larger patch of land, and during a greater number of hours each day, than a cold blooded crocodile. So a bear might survive in a more calorie-depleted environment despite its increased appetite.

what if their eggs had better protection compared to the dianosor egg?

> "The real question is, how did the others—how did any animal—manage to survive? [Impact theorists] have got to come up with a hypothesis that puts equal weight on survival. So many of these catastrophists want to kill the dinosaurs [that] they forget the rest of the biota. Birds, mammals, and amphibians managed to survive, and that tells you that there is something wrong."

This is what always bugged me about the impact extinction scenarios. If it really had that devastating an impact on the entire planet, then why only the dinosaurs and not all land vertebrates?

Does that mean that none of the dinosaurs would have been sufficiently sheltered and capable of surviving the aftermath, but birds, mammals and amphibians could?

Yes. No.

Mammals didn't survive as such. The big ones died, as did many, many other species. As the paper points out, "mammals surviving the K-T event were generally rat-sized or smaller".

Generally, there are more small animals than big, I mean more individuals of a particular species. There are more flies than elephants. If the chance of of an individual dying in the Big Oven is 99%, greater numbers help the species survive.

This deserves an upvote for the title alone. :-)

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