In the popular notion of comets or large meteorites causing the extinction of dinasaurs, what's the explanation for the continued existence of turtles and alligators? Did they simply duck it out in the mud? If that's the case, why did the marine dinosaurs crap out?
comets and dinasaurs
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Bikewer
Penultimate Amazing
I recall reading that at about the time of the extinction (which was an "event" that went on for some time) dinosaurs were not particularly diverse. Bob Bakker, (The Dinosaur Heresies) indicated that North America was populated by huge herds of rather specialized grazers, with an incidence of predators appropriate to their numbers.
The cometary impact is presumed to have caused something along the lines of the "nuclear winter", causing a massive die-off of plant life on land. This would have doomed the grazers, and their predators as well.
Large scale die-off of ocean flora would have impacted "krill", which would have decreased larger fish populations as well. Eventually, unable to support the larger predator oceanic dinosaurs.
Creatures such as crocodiles have a different lifestyle; essentially ambush predators able to eat nearly anything. The really big ones would likely have perished for lack of prey, but smaller species would have found sufficient foodstuffs.
Likewise turtles are omnivores; able to eat both plant foods and other critters as well.
Seems to me that the smaller and less-specialized creatures would have found room to flourish, while the highly-specialized dinosaurs would have had trouble.
The cometary impact is presumed to have caused something along the lines of the "nuclear winter", causing a massive die-off of plant life on land. This would have doomed the grazers, and their predators as well.
Large scale die-off of ocean flora would have impacted "krill", which would have decreased larger fish populations as well. Eventually, unable to support the larger predator oceanic dinosaurs.
Creatures such as crocodiles have a different lifestyle; essentially ambush predators able to eat nearly anything. The really big ones would likely have perished for lack of prey, but smaller species would have found sufficient foodstuffs.
Likewise turtles are omnivores; able to eat both plant foods and other critters as well.
Seems to me that the smaller and less-specialized creatures would have found room to flourish, while the highly-specialized dinosaurs would have had trouble.
yes, but:
weren't there also small dinosaurs that went down?
Were there no omnivorous dinos?
I have recently learned that female turtles (of some species) can stash sperm for several years, if circumstances dictate.
I don't know if the same is true for alligators or dinosaurs. Could this be part of the explanation?
weren't there also small dinosaurs that went down?
Were there no omnivorous dinos?
I have recently learned that female turtles (of some species) can stash sperm for several years, if circumstances dictate.
I don't know if the same is true for alligators or dinosaurs. Could this be part of the explanation?
Paulhoff
You can't expect perfection.
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Dinosaurs, warm to hot blooded, and fast growing, needing lots of food to live.
Turtles and alligators are cold blooded, slow growing needing little food to live.
Also dinosaurs where not the only things to disappear.
http://news.bbc.co.uk/2/hi/science/nature/7181993.stm
Paul
Turtles and alligators are cold blooded, slow growing needing little food to live.
Also dinosaurs where not the only things to disappear.
http://news.bbc.co.uk/2/hi/science/nature/7181993.stm
Paul
Kotatsu
Phthirapterist
I had a look in my copy of Fastovsky and Weishampel's otherwise excellent "The Evolution and Extinction of the Dinosaurs", to see if it had any suggestion. I did, eventually, find a brief mention --- on page 440 --- of patterns in survival of terrestrial vertebrates after the K/T boundary. They refer to Archibald and Bryant, who apparently made a study on exactly this, trying to figure out if there were patterns to what survived and what didn't. Their conclusions were that land-living organisms showed only a 10% survivorship, whereas those that lived in limnic areas (rivers, lakes, and so on) showed a 90% survival rate. They also found that "small vertebrates are favored over large vertebrates, ectotherms over endotherms, and non-amniotes over amniotes".
Sadly that is all the have to say on the subject, but their reference list leads to the following publications:
- Archibald, 1996: Dinosaur Extinction and the End of an Era. Columbia University Press.
- Archibald & Bryant, 1990: Differential Cretaceous/Tertiary extinction of nonmarine vertebrates; evidence from northeastern Montana. In: Sharpton & Ward (eds.), Global Catastrophes in Earth History; an Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality. Geological Society of America Special Paper no. 247, pp 549-562.
There are some more references to journal articles. I could see if my university has access to those, if you'd like.
Sorry if this was not very informative. I'll look a bit more in this book and see if I get some more clues elsewhere.
Sadly that is all the have to say on the subject, but their reference list leads to the following publications:
- Archibald, 1996: Dinosaur Extinction and the End of an Era. Columbia University Press.
- Archibald & Bryant, 1990: Differential Cretaceous/Tertiary extinction of nonmarine vertebrates; evidence from northeastern Montana. In: Sharpton & Ward (eds.), Global Catastrophes in Earth History; an Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality. Geological Society of America Special Paper no. 247, pp 549-562.
There are some more references to journal articles. I could see if my university has access to those, if you'd like.
Sorry if this was not very informative. I'll look a bit more in this book and see if I get some more clues elsewhere.
Delvo
Дэлво Δε&#
Mammals (of the time) and birds are warm-blooded, but small, so they needed more food than similar-sized reptiles, but less than larger animals. Factors that helped them survive despite their warm-bloodedness would include birds' ability to get food from a wider area by flying, and mammals' tendency to be nocturnal and/or ovovorous.
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CapelDodger
Penultimate Amazing
Follow the food-chain.
Some food-chains are anchored on creatures that eat dead stuff - and there would have been a lot of that about. This ties in with Kotatsu's point about the limnic environments, which would have been provided with a flow of nutrients from all those land-based critters and plants that died with nothing much around to eat them.
One branch of dinosaurs did survive - the birds. They're small, mobile, and many species will have fed on insects or fish. The fruit-and-seed eaters will have died off, but those niches have been filled subsequently (this was a long time ago, after all).
Termites did OK, as did species that live off termites. Any species with a food-chain based on leaf-litter did OK (which includes a lot of insects and worms). Turtles eat jellyfish, which eat plankton, which did OK from the flow of nutrients. Crocodilians eat big fish, which eat smaller fish, which eat plankton and algae and insects. Amphibians are by nature limnic. And so on.
Follow the food-chain. If you need fresh leaves or fresh herbivores, forget it.
Some food-chains are anchored on creatures that eat dead stuff - and there would have been a lot of that about. This ties in with Kotatsu's point about the limnic environments, which would have been provided with a flow of nutrients from all those land-based critters and plants that died with nothing much around to eat them.
One branch of dinosaurs did survive - the birds. They're small, mobile, and many species will have fed on insects or fish. The fruit-and-seed eaters will have died off, but those niches have been filled subsequently (this was a long time ago, after all).
Termites did OK, as did species that live off termites. Any species with a food-chain based on leaf-litter did OK (which includes a lot of insects and worms). Turtles eat jellyfish, which eat plankton, which did OK from the flow of nutrients. Crocodilians eat big fish, which eat smaller fish, which eat plankton and algae and insects. Amphibians are by nature limnic. And so on.
Follow the food-chain
. If you need fresh leaves or fresh herbivores, forget it.Kotatsu
Phthirapterist
Follow the food-chain
By the empress, that's an excellent explanation! It sparked a memory:
[derail]
I read a book last year which was about this actual event, but in a fictional setting where some humans are transported to a few days before the meteor hits, and they can't get back. The impact occurs, and the people in the book manage to survive, and witness exactly that: leaf eaters disappear, but the scavengers remain. And so on.
I should have made that connection earlier^^.
The book, in case anyone is interested, is Cretaceous Sea by Will Hubbell, and I found it to be nice, but not outstanding.
[/derail]
Kotatsu
Phthirapterist
Well, Baryonyx ate fish, but that's as close as you can get, I guess...
Loss Leader
I would save the receptionist., Moderator
Don't gloss over the fact that many alligator species did become extinct. The so-called "dino-crocs" are now as extinct as all of the large dinosaurs. http://en.wikipedia.org/wiki/Sarcosuchus_imperator
Paulhoff
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A few points. Firstly, as already mentioned, far more things than just dinosaurs died out. Secondly, the dinosaurs probably didn't just disappear overnight. There are various different theories about the how and why, some which would only take a few thousand years, others which would take hundreds of thousands, or even longer. Either way, it's not a case of some things suddenly dying and others not, it's a case of some things being able to adapt to a new environment and others not. As already mentioned, large, specialised animals will find it much harder to adapt and so are much more likely to die out.
Thirdly, possibly most importantly, is the definition of "dinosaur". Many things often labelled dinosaurs actually aren't, and many of them would have been much closer to reptiles or birds. For example, dimetrodon is one of the "classic" dinosaurs that most people would recognise, but isn't a dinosaur at all and is actually most closely related to mammals. None of the aquatic things often called dinosaurs, such a plesiosaurs, are dinosaurs, and the same for flying ones as well. Many of these belong to the archosaurian group, but so do crocodiles and birds.
The question of why certain species died out and why others survived is an interesting one, but the simplistic view of dinosaurs all dying out and everything else being OK just isn't true. Some dinosaurs died out, along with lots of things that weren't dinosaurs. Other dinosaurs didn't die out and their descendants are still around today.
Thirdly, possibly most importantly, is the definition of "dinosaur". Many things often labelled dinosaurs actually aren't, and many of them would have been much closer to reptiles or birds. For example, dimetrodon is one of the "classic" dinosaurs that most people would recognise, but isn't a dinosaur at all and is actually most closely related to mammals. None of the aquatic things often called dinosaurs, such a plesiosaurs, are dinosaurs, and the same for flying ones as well. Many of these belong to the archosaurian group, but so do crocodiles and birds.
The question of why certain species died out and why others survived is an interesting one, but the simplistic view of dinosaurs all dying out and everything else being OK just isn't true. Some dinosaurs died out, along with lots of things that weren't dinosaurs. Other dinosaurs didn't die out and their descendants are still around today.
Delvo
Дэлво Δε&#
BTW, there's also the question of what made certain kinds of plants go extinct and not others...
Yes, which is why I'm wondering if the longevity of the seed (or fertilized egg) is a factor.
Again, I think it will have been more to do with adaptability than anything else. Plants which can only survive under a small set of conditions will have dies out, while those that can live pretty much anywhere would do better. Temperature, rainfall, amount of sunlight, soil pH, availability of nutrients and so on would all have changed. In addition, if the species they rely on for pollination dies out, so will the plants. It won't matter how long seeds can last if they can't survive once they germinate. And it matters even less if there aren't any seeds to start with.
CapelDodger
Penultimate Amazing
Crocodilians pre-date the dinosaurs, and they're very good at what they do (they're still with us now, after all) so it's unlikely that dinosaurs could muscle them out of their niches. I'm not so sure about turtles, but I suspect the same applies.
As to plants, there are some whose seeds can lie dormant for years until the right conditions occur. The sudden greening of deserts after rainfall is evidence of that.
That probably played a part.
MG1962
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Dinosaurs were in some type of trouble before the comet strike. Although their biomass remained as strong as ever, diversity was crashing. Some estimates put the species numbers as low as a fifth what they were even 20 million years earlier.
As others have pointed out, the marine reptiles crashed because of the food chain. Huge populations of marine creatures such as anomites etc all went down at the same time
As others have pointed out, the marine reptiles crashed because of the food chain. Huge populations of marine creatures such as anomites etc all went down at the same time
shadron
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Yes, it was the same time as the creation of the Deccan Traps, a huge outpouring of lavas in India. I remember watching the BBC series Walking with Dinosaurs and they emphasized that the late Cretaceous seems to have been a bad time for the biosphere, mostly thought to be atmospheric pollution. The meteor seems to have been the icing on the cake that ended the Cretaceous with an iridium rich bang.
It should also be remembered that the top predictors in the food chain after the KT boundary were giant birds, so it would seem that the dinosaurs weren't really stopped at all by the KT, but rather a lot of their competition was.
It should also be remembered that the top predictors in the food chain after the KT boundary were giant birds, so it would seem that the dinosaurs weren't really stopped at all by the KT, but rather a lot of their competition was.
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