What is the current scientifically accepted theory why species of crocodiles and turtles (and other reptiles for that matter) that lived with Dinosaurs survived whatever eliminated the Dinosaurs? I realize that crocodiles and turtles are not closely related to dinosaurs, but they lived in the same places and presumably had the same environmental pressures. I have always wondered this and have never found a satisfying answer.
The currently accepted theory is that the thing that wiped out the large dinosaurs was an asteroid strike, which pitched the earth under a cloud for (scores? hundreds? thousands?) of years, severely altering the climate and causing a mass extinction, including lots of plant life, which reduced the food supply.
The currently accepted theory for why many reptiles survived is that they have relatively low metabolisms and therefore don’t require as much food.
The currently accepted theory for why most dinosaurs died out is because they required more food and the featherless ones couldn’t adjust to climate change well.
The small, feathered ones survived.
Some did, but a lot didn’t. Enantiornithine birds were just as small and feathered as neornithine birds, yet they went completely extinct.
An alternative theory I have heard points out that both of these surviving groups lived primarily in water- and suggest that as water, especially large bodies of water, is better at keeping a stable temperature than air, creatures living in water had less dramatic temperature changes to deal with than the land based creatures of a similar size.
This doesn’t really answer why the pleiosaurs also died out though.
So we know that the metabolism of crocodiles, turtles and dinosaurs were very different. How did we deduce that? Based on their lifestyles? I had assumed there were slow moving, semi-aquatic dinos that must have competed directly with crocs. And wouldn’t the herbivorous turtles be eating the same thing as the herbivorous dino’s?
So being able to go a long time without eating much may have saved crocs and turtles from extinction?
As you mentioned, a lot of aquatic dinos died out about the same time and their terrestrial counterparts, yet other aquatic reptiles managed to survive somehow.
No, carnivorous dinosaurs were all terrestrial bipeds.
Based on many things. To my mind, the most convincing are the differences in the fossilized bones at the microscopic level between cold-blooded and warm-blooded animals.
Dinosaurs in the Cretaceous’ bones have many more pores, like warm-blooded animals.
There’s also that birds, which are either a small branch of dinosaurs that are flourishing, or their own class that evolved from dinosaurs, but it’s mostly a semantics argument, are warm-blooded.
Somewhat convincing is the ratio of vegetarian to carnivorous dinosaur fossils found - about the ratio one would expect for a warm-blooded (high metabolism) group. A warm-blooded population requires a lot more vegetarians to support the meat-eaters. But carnivores eat cross-group, of course, which is why it’s not as convincing to me. Crocs could eat vegetarian dinosaurs just as well as raptors could.
Plesiosaurs are admittedly problematic. They disappear right at the K-T boundary, but sharks survived. And not just small ones. *Cretoxyrhina *was a big boy. Don’t know why sharks survived but plesiosaurs didn’t.
Perhaps the difference is the ability of turtles and crocodilians to hibernate, or estivate, in conditions of extreme heat or cold. At such times they bury themselves in the mud (which might also have provided protection).
I assume dinosaurs (and plesiosaurs) did not have this ability.
Did terrestrial dinos bury their eggs like turles and crocs? How did fully aquatic dinos deal with eggs?
There were no fully aquatic dinosaurs.
Pleisiosaurs and Ichthyosaurs and Mososaurs and so on were marine reptiles, but they weren’t dinosaurs.
The notion that sauropods were aquatic grazers has been thoroughly discredited for 50 years.
That’s true, Lemur866, but I think you know what he means. It’s a valid question if other large egg-laying critters behaved similarly to each other.
As far as I know, nobody knows about plesiosaur’s egg-laying habits. None have ever been discovered.
Poking around, it seems that in some parts of the world, sharks went completely extinct. (warning - pdf) So they did have difficulties.
Another item I read about this suggested that anything over about 5 pounds died; the issue was climate and food supply. At least one breeding pair has to survive in some location, and the bigger animals did not have the resources to survive. Another problem may simply be erratic destruction - some small areas survived sufficiently to allow their occupants to live, even while meteroid hot flashes and then nuclear-winter-scale fallout destroyed much of the ecology.
Nice user name / post combo.
That’s a good theory.
And just to nitpick, which I normally don’t like to do but since this is GQ I’ll go ahead, according to Wiki they “brumate” instead of “hibernate”.
The combination of metabolism and size and the resulting food requirements must have been a major factor. There are reports of adult crocodiles surviving up to a year with eating. Seems unlikely that a large and warm blooded animal could survive with such a restricted food supply.
There were many species of animals that survived the major extinction, but were not suitably adapted to the environment that followed, and became extinct gradually afterwards. There may have been dinosaurs which survived initially but never established enough of a foothold for long enough to leave evidence of post extinction life.
We do know that Ichthyosaurs, at least some of them, had live birth–there are famous fossils of female Ichthyosaurs who died while giving birth: Mijndomein
Thing is, lots and lots of creatures of all types and habitats went extinct. The only thing the survivors have in common is that enough of them survived (perhaps only a single breeding pair or gravid female) to found a new population after the event.
So it’s perfectly possible that crocodiles survived simply because a particular burning tree fell 1 foot to the left and didn’t crush one particular nest, while plesiosaurs went extinct because another tree fell 1 foot to the right and crushed another particular nest. That said, there was probably bias in the random extinction process, as particular species in particular habitats with particular lifestyles were more vulnerable than others. So even if freshwater aquatic reptiles had a better shot at avoiding extinction, that doesn’t mean we can say for sure why some freshwater aquatic lineages survived and others didn’t.
Just to comment on this: crocodilians are fairly closely related to dinosaurs. Crocodiles are the non-bird group most closely related to birds. And crocodiles are more closely related to birds than they are to other reptiles. (There is/was some dispute over the relationships among bird, crocodiles and dinosaurs.)
That’s a great point. For all I know, plesiosaurs gave birth to live young. In fact, they did.
Icthyosaurs were gone by the KT boundary, though.
I thought a brewmate was the same thing as a beer buddy. 