Mammals were almost destroyed with the dinosaurs 65 million years ago

Some inherent feature of mammal biology allowed them to adapt after global disaster.

Read the whole story

 

[Alhazred]

Wheels Of Confusion[/url]":1127qsnf]

Wheels Of Confusion[/url]":1127qsnf]

Viruses laugh at your puny prokarya.

Psh, we're talking about living things here. Viruses need not apply! :devious:

(ง'̀-'́)ง

(ง'̀-'́)ง . . . Q(｀⌒´Q)

I see you've pioneered a whole new level of textual ninjitsu.

 

[Colm]

Alhazred[/url]":2nn1auee]

Wheels Of Confusion[/url]":2nn1auee]

Wheels Of Confusion[/url]":2nn1auee]

Viruses laugh at your puny prokarya.

Psh, we're talking about living things here. Viruses need not apply! :devious:

(ง'̀-'́)ง

(ง'̀-'́)ง . . . Q(｀⌒´Q)

I see you've pioneered a whole new level of textual ninjitsu.

(╯°□°)╯︵ ┻━┻ ︵ ╯(°□° ╯)

 

[Alhazred]

Colm[/url]":1ngvu1z9]

Alhazred[/url]":1ngvu1z9]

Wheels Of Confusion[/url]":1ngvu1z9]

Wheels Of Confusion[/url]":1ngvu1z9]

Viruses laugh at your puny prokarya.

Psh, we're talking about living things here. Viruses need not apply! :devious:

(ง'̀-'́)ง

(ง'̀-'́)ง . . . Q(｀⌒´Q)

I see you've pioneered a whole new level of textual ninjitsu.

(╯°□°)╯︵ ┻━┻ ︵ ╯(°□° ╯)

Hmmmph!

 

[Luddite Curmudgeon]

Alhazred[/url]":2g33gt69]

DStaal[/url]":2g33gt69]
I'm not finding anything that will tell me quickly, but it wouldn't surprise me if grasses were advance colonists right from the start. A lot of their structure is designed for quick growth that can be sustained despite setbacks.

As another piece in there - grasses are fairly likely to use the C4 carbon path, vs. the C3 path used overall. The advantages of the C4 path include better resistance to drought and other resource starvation, so it's likely they dominated in the immediate aftermath.

Remarkably little is actually known for sure about the evolution of grasses. At 55 mya we have definitely got grass, at 66 mya there are recently analyzed coprolites containing probable grass (putting it more definitely into the Cretaceous, though its always been assumed to have existed in some degree back then). Multituberculates have suspiciously grass-eating like adaptations at 107 mya, and phylogenetic evidence indicates grasses may well have diverged in the early Cretaceous/End Jurassic.

C4 only exists in the PACMAD clade, and has evolved numerous times in that group. That would kind of indicate to me its a more recent development, though I doubt there's much way to really know for sure, unless phylogenetics can unravel the mystery.

Here's the thing, if grass really existed as far back as the Earliest Cretaceous its hard to imagine that dinosaurs didn't evolve to deal with it. Its also pretty unclear if it was extensive at the K-Pg or not. So whether it played any role in dinosaur extinction is hard to say. As with other changes in general the big question would be why would mammals adapt to these changes but not dinosaurs? There could be reasons of course, related to basic physiological constraints on each type of organism.

The possibility exists that they didn't need to evolve to eat grass. Especially if the other plants were plentiful and grew fast. I mention grass because after a forest fire today (or any event that leaves bare ground), the first thing that comes back are the grasses. Then some taller plants. Large things such as trees take way longer. So while the grasses may have been there after a forest fire, before that perhaps there was other fauna that grew as fast, and the plant eaters just started eating those.

Somebody mentioned a long recovery time doesn't help a large plant eater who needs food NOW. So it goes back to what fauna recovers fastest, and what animals of any sort would still be around to eat said plants. A long-necker will have issues eating small plants low to the ground, but if that's all that's there. And if they're constantly mowing the small plants before they become the huge plants, those big plants will never recover to the point where they can support the large animals. At least until they die out, and as long as there's enough seed survival to repopulate the ecosystem. And so forth.

 

[DStaal]

Alhazred[/url]":304wx5w8]

DStaal[/url]":304wx5w8]
I'm not finding anything that will tell me quickly, but it wouldn't surprise me if grasses were advance colonists right from the start. A lot of their structure is designed for quick growth that can be sustained despite setbacks.

As another piece in there - grasses are fairly likely to use the C4 carbon path, vs. the C3 path used overall. The advantages of the C4 path include better resistance to drought and other resource starvation, so it's likely they dominated in the immediate aftermath.

Remarkably little is actually known for sure about the evolution of grasses. At 55 mya we have definitely got grass, at 66 mya there are recently analyzed coprolites containing probable grass (putting it more definitely into the Cretaceous, though its always been assumed to have existed in some degree back then). Multituberculates have suspiciously grass-eating like adaptations at 107 mya, and phylogenetic evidence indicates grasses may well have diverged in the early Cretaceous/End Jurassic.

C4 only exists in the PACMAD clade, and has evolved numerous times in that group. That would kind of indicate to me its a more recent development, though I doubt there's much way to really know for sure, unless phylogenetics can unravel the mystery.

Here's the thing, if grass really existed as far back as the Earliest Cretaceous its hard to imagine that dinosaurs didn't evolve to deal with it. Its also pretty unclear if it was extensive at the K-Pg or not. So whether it played any role in dinosaur extinction is hard to say. As with other changes in general the big question would be why would mammals adapt to these changes but not dinosaurs? There could be reasons of course, related to basic physiological constraints on each type of organism.

Hence my theory that the dinosaurs were probably starting to adapt to the rise of grass, but still preferred other plant sources. (As grasses weren't dominant anyway, most likely - they are the new kid on the block.) You get a worldwide cataclysm, and suddenly the fast-growing fast-spreading grasses are more common, but they aren't as good a food source for the large plant-eating dinosaurs.

Meanwhile they are just fine food sources for the small, seed-eating mammals: Their seeds aren't any harder to digest than other seeds. Adaptations to actually eat the grass can come later, when there isn't as much competition in that space.

Anyway, just a hypothesis, and I don't think it would be enough in and of itself to cause extinction, but I think it could be another small push for the mammals and against the dinosaurs. Some of this depends on when and how some specific features of grass evolved anyway - specifically their tough cell walls.

 

[Nostromo21]

Has any of the science ever addressed why ocean-dwelling dinosaurs also died out at about the same time/rate as did the land-bound ones...? Surely the asteroid impact (pardon the pun!) would have been much less in the oceans...or am I missing something obvious...? :-/

 

[Hat Monster]

Nostromo21[/url]":3q7ubztp]Has any of the science ever addressed why ocean-dwelling dinosaurs also died out at about the same time/rate as did the land-bound ones...? Surely the asteroid impact (pardon the pun!) would have been much less in the oceans...or am I missing something obvious...? :-/

There were no oceanic dinosaurs.

There were large marine reptiles like icthyosaurs, mosasaurs, plesiosaurs, pliosaurs, etc. They weren't dinosaurs, nor even particularly closely related to them. Their food chain collapsed too.

 

[Router66]

Alhazred[/url]":1a03p1er]

DStaal[/url]":1a03p1er]
I'm not finding anything that will tell me quickly, but it wouldn't surprise me if grasses were advance colonists right from the start. A lot of their structure is designed for quick growth that can be sustained despite setbacks.

As another piece in there - grasses are fairly likely to use the C4 carbon path, vs. the C3 path used overall. The advantages of the C4 path include better resistance to drought and other resource starvation, so it's likely they dominated in the immediate aftermath.

Remarkably little is actually known for sure about the evolution of grasses. At 55 mya we have definitely got grass, at 66 mya there are recently analyzed coprolites containing probable grass (putting it more definitely into the Cretaceous, though its always been assumed to have existed in some degree back then). Multituberculates have suspiciously grass-eating like adaptations at 107 mya, and phylogenetic evidence indicates grasses may well have diverged in the early Cretaceous/End Jurassic.

C4 only exists in the PACMAD clade, and has evolved numerous times in that group. That would kind of indicate to me its a more recent development, though I doubt there's much way to really know for sure, unless phylogenetics can unravel the mystery.

Here's the thing, if grass really existed as far back as the Earliest Cretaceous its hard to imagine that dinosaurs didn't evolve to deal with it. Its also pretty unclear if it was extensive at the K-Pg or not. So whether it played any role in dinosaur extinction is hard to say. As with other changes in general the big question would be why would mammals adapt to these changes but not dinosaurs? There could be reasons of course, related to basic physiological constraints on each type of organism.

On the evolution of grasses, take a look at this one. It was announced only last year and it effectively pushes the grass timeline some 40my back - at least.
http://www.sci-news.com/paleontology/sc ... 02482.html

 

[jimcox]

Alhazred[/url]":1ybi6d2e]

jimcox[/url]":1ybi6d2e]

Alhazred[/url]":1ybi6d2e]

Fatesrider[/url]":1ybi6d2e]

El Guapo[/url]":1ybi6d2e]Was I the only one that read the title as "Millennials were almost destroyed with the dinosaurs ..."?

You just need more coffee.

I'm wondering if the egg-laying had more to do with it than anything else. If, as has been reported, the entire world was thrown into cold due to the dust in the air for a lengthy time, then only brooding animals, which sit on eggs to keep them warm, and mammals, who bear live young, would have a chance to reproduce.

Dinosaurs, from what I've gathered and seen of their nests, didn't brood. And some of their strategies for keeping eggs warm (like covering them in biodegrading matter) wouldn't have been sufficient to keep that matter warm if the temperature plummets even more than usual.

If one assumes already living dinosaurs could survive the cold, it may be their eggs couldn't, or couldn't in enough numbers to remain viable. The fossil record doesn't really have the resolution to distinguish the generations, but the speed at which the dinosaurs died off after the boundary suggests it could have been well within a generation of two of the event - maybe 100 years tops.

Then, without the pressure of the dinosaurs hunting them, the mammals had a BETTER chance at survival and once the food supplies recovered, they multiplied (which is exactly what happens in nature today).

Just a thought that I didn't see offered as a potential reason for the ascendancy of mammals, and a reason birds survived, in the article.

But then how do you account for lizards, snakes, amphibians, crocodillians, turtles, etc? Any explanation that works for them should also work for dinosaurs. Here's what bothers me about the whole thing. Any of these reasons might well be true, for SOME species, but why EVERY dinosaur?

One thing that is pretty clear, NOTHING above a mass of about 2 kg survived on land. Now we know very few species, even of mammals (and I'm going to hypothesize birds follow the same pattern) survived. Sounds like the number of individuals, and the total biomass in any given area which persisted was VERY small. The land was ALMOST completely sterilized. If the ecosystem's carrying capacity was extremely low, then it makes sense, of the few individuals who survived, only small species where that number was a breeding population that fell below the ecosystem energy cycling limit (IE could get enough food) could possibly survive. If it wasn't that bad, then almost certainly a few dinosaur species would have persisted, even if only for a fairly short time period in geological terms. So what we see here must logically be something like a 99.95% kill. Only something as small a mouse or wren, living in countless millions had ANY chance to pull through.

From Wikipedia:
"The Cretaceous–Paleogene (K–Pg) extinction event,[a] also known as the Cretaceous–Tertiary (K–T) extinction, was a mass extinction of some three-quarters of the plant and animal species on Earth—including all non-avian dinosaurs—that occurred over a geologically short period of time[2][3][4] approximately 66 million years ago.[3] With the exception of some ectothermic species in aquatic ecosystems like the leatherback sea turtle and crocodiles, no tetrapods weighing more than 55 pounds (25 kilos) survived."

That is a lot more than 2 kg. It makes sense that very large creatures would be more susceptible to extinction. If you have a climatic event where there is very little vegetation, even for a short period of time, large warm blooded herbivores would die off because of lack of food. Cold blooded creatures are much more able to survive if they don't freeze. Alligators and many other reptiles can go for months without eating. Extreme events are often going to favor smaller creatures (except cold blooded creatures) for a large number of fairly obvious reasons. Also, the percentage of species that went extinct was smaller than you imply. It was far from "total sterilization". Insect species probably were not affected much at all. I think the only large extinction of insect species was the Permian-Triassic extinction event.

Name something over 2kg that survived that wasn't aquatic. That's the cutoff I've seen cited in a number of fairly knowledgeable discussions of the topic. Yes, AQUATIC reptiles of a larger size PERHAPS survived, BUT a small crocodile (say a hatchling) might well be your survivor in that case. As you say, they can eat little and often estivate. They grow slowly, so they would remain small and requiring less food for a substantial time period. Turtles are at least aquatic (and most such species are in the under 2kg range, or close to it) and many are ocean dwellers, thus much less affected.

As for insects, they exist is truly mind-blasting numbers. There are said to be something on the order of a billion ants for every hectare of land outside the arctic. 99.95% losses would be practically meaningless to those kinds of numbers in terms of SOME individuals surviving. They are also classic r-strategists, which would clearly be advantageous.

You should review the actual physical effects of the Chixulub event as well. Its actually pretty damned amazing that as much survived as did. The top 1 meter of the ENTIRE OCEAN was boiled away. The air temperature over the entire globe was raised to the flash point of dry organic material, and pelted with a rain of debris significant enough to leave several inches on average over the whole surface of the Earth. I don't see anything incompatible with the notion that 1 out every 2,000 rats managed to survive, and not much else. Again, if this was not so, then why NOT ONE SINGLE non-avian dinosaur? Surely some of them were small, adaptable, could eat seeds/nuts/insects/carrion/something. They just weren't quite as small and numerous as the mammals. 1 in 2000 of THEM wasn't enough.

I have seen a lot of things that indicate that it was not anywhere near as bad as you describe. In your original post, you give very specific numbers, such as 99.95%. We do not know how many creatures survived at all. That number is completely arbitrary. Even if we magically had such a number, it wouldn't be a useful number. The catastrophe obviously would have effected different species in different habitats very differently. Many obviously suffered 100% die off. Other creatures, we just don't know. Also, a large number of aquatic species did die out. The oceans were not spared.

As for "anything over 2 kg", that is a completely arbitrary number also. I don't think that an alligator would need to be small to have survived. There still would have been some food and they don't need to eat much. They are also not picky about what they eat; smaller alligators could have been on the menu along with just about any other creature. Maybe there was a platypus ancestor that weighed 3 kg that survived. I will name him Fred. There, I named one. Anyway, there was not some arbitrary weight limit. When you cut off photosynthesis for possibly years, what ecosystems are left? Basically ecosystems where the base of the ecosystem feeds on rotting plant material. This is essentially a swamp ecosystem or perhaps a very moist forest floor. Dry material doesn't support much invertebrate life. There still would have been insect larvae, worms, snails, slugs, and other invertebrates that feed on rotting plant material or the fungus that grows on them in swamp-like ecosystems.

So, what was selected for rather than selecting some arbitrary weight limit? The creatures that would still survive in these detritus based ecosystems would be insectivores and other generalist omnivores similar to rats that will eat just about anything. Any creatures dependent on active plant growth would die off. This would include herbivores, the predators that hunt them, the scavengers that scavenged them, and several other niches (egg eaters, etc). Were there any insectivore dinosaurs? Probably not. If there had been a larger termite eating dinosaur, then maybe it would have survived. Termites eat dead plant material; probably plenty of that around. Just about any dinosaur was too large to be an insectivore. Most insectivores are nocturnal, since most insects come out at night; dinosaurs are not thought to have been nocturnal either. Things were probably still very tough though, or some small dinosaurs would have survived by eating the small mammals, birds, amphibians, fish, and reptiles that did survive. I would suspect that the birds and mammals that survived were those that already hunted in such swamp-like ecosystems. Similar event happened in the oceans. Creatures that fed high in the water column and were dependent on active photosynthesis died out in large numbers, The bottom dwellers did okay since those ecosystems are based on detritus falling from above.

Also, for the time after the impact event, while insectivores and similar creatures were selected for, the very small ones may actually have been selected against. Even under normal conditions, very small mammals or birds (shrews or hummingbirds for example) live only a very short time away from starvation. With an uncertain food supply, such small size could have been detrimental. Also, temperatures could have been much colder than before. This also selects for larger creatures that do not have to expend so much energy to keep warm and can store more fat for lean times. Those that survived may have been around the equator; it may have been much to cold any places too far north or south. They could have grown larger very quickly as they spread back north to colder climates as plant life recovered.

 

[jimcox]

Hat Monster[/url]":31lxz09t]It's not that the extinction was "picky". Ecosystems don't work like that.

It's that a huge number of keystone species were wiped out in a short span of time and primary productivity was reduced to at least a fifth of its normal capacity.

This caused the highly advanced and very derived animals to suffer most. They're the ones which fitted in so well that they could only adjust slowly to long term changes. This is why the "gradual cooling" (there were Antarctic dinosaurs!) and "three million years of vulcanism" theories don't really explain it all, as all that had happened before and the dinosaurs had barely noticed.

The less specialised, less advanced won out, but even they took heavy losses.

However, even some specialists could make it if they could switch to alternative food. Dung beetles appeared in the Jurassic to exploit on the mountains of dung that the sauropods produced. However, as detritus feeders, they could switch to any other source of organic material. They're still around today. The various biting insects which followed herds of sauropods around are not, as they couldn't. The pterosaurs which followed the sauropods around to feed on these insects aren't. The microorganisms specialised to live in and on them are not. To these, the sauropods were their keystone species. The extinction of one group (or even just one species) has a knock on that everything relying on them also goes. Then everything relying on them has to go.

Knocking out just one big, influential species can collapse an entire ecosystem. Knocking out nearly all of them causes a cataclysm.

Was it actually that cold in the Antarctic at that time though? The continent was not isolated at the south pole at the time, so it could have had warm ocean currents around it.

 

[JPan]

jimcox[/url]":3mj95jrv]

Alhazred[/url]":3mj95jrv]

jimcox[/url]":3mj95jrv]

Alhazred[/url]":3mj95jrv]

Fatesrider[/url]":3mj95jrv]

El Guapo[/url]":3mj95jrv]Was I the only one that read the title as "Millennials were almost destroyed with the dinosaurs ..."?

You just need more coffee.

I'm wondering if the egg-laying had more to do with it than anything else. If, as has been reported, the entire world was thrown into cold due to the dust in the air for a lengthy time, then only brooding animals, which sit on eggs to keep them warm, and mammals, who bear live young, would have a chance to reproduce.

Dinosaurs, from what I've gathered and seen of their nests, didn't brood. And some of their strategies for keeping eggs warm (like covering them in biodegrading matter) wouldn't have been sufficient to keep that matter warm if the temperature plummets even more than usual.

If one assumes already living dinosaurs could survive the cold, it may be their eggs couldn't, or couldn't in enough numbers to remain viable. The fossil record doesn't really have the resolution to distinguish the generations, but the speed at which the dinosaurs died off after the boundary suggests it could have been well within a generation of two of the event - maybe 100 years tops.

Then, without the pressure of the dinosaurs hunting them, the mammals had a BETTER chance at survival and once the food supplies recovered, they multiplied (which is exactly what happens in nature today).

Just a thought that I didn't see offered as a potential reason for the ascendancy of mammals, and a reason birds survived, in the article.

But then how do you account for lizards, snakes, amphibians, crocodillians, turtles, etc? Any explanation that works for them should also work for dinosaurs. Here's what bothers me about the whole thing. Any of these reasons might well be true, for SOME species, but why EVERY dinosaur?

One thing that is pretty clear, NOTHING above a mass of about 2 kg survived on land. Now we know very few species, even of mammals (and I'm going to hypothesize birds follow the same pattern) survived. Sounds like the number of individuals, and the total biomass in any given area which persisted was VERY small. The land was ALMOST completely sterilized. If the ecosystem's carrying capacity was extremely low, then it makes sense, of the few individuals who survived, only small species where that number was a breeding population that fell below the ecosystem energy cycling limit (IE could get enough food) could possibly survive. If it wasn't that bad, then almost certainly a few dinosaur species would have persisted, even if only for a fairly short time period in geological terms. So what we see here must logically be something like a 99.95% kill. Only something as small a mouse or wren, living in countless millions had ANY chance to pull through.

From Wikipedia:
"The Cretaceous–Paleogene (K–Pg) extinction event,[a] also known as the Cretaceous–Tertiary (K–T) extinction, was a mass extinction of some three-quarters of the plant and animal species on Earth—including all non-avian dinosaurs—that occurred over a geologically short period of time[2][3][4] approximately 66 million years ago.[3] With the exception of some ectothermic species in aquatic ecosystems like the leatherback sea turtle and crocodiles, no tetrapods weighing more than 55 pounds (25 kilos) survived."

That is a lot more than 2 kg. It makes sense that very large creatures would be more susceptible to extinction. If you have a climatic event where there is very little vegetation, even for a short period of time, large warm blooded herbivores would die off because of lack of food. Cold blooded creatures are much more able to survive if they don't freeze. Alligators and many other reptiles can go for months without eating. Extreme events are often going to favor smaller creatures (except cold blooded creatures) for a large number of fairly obvious reasons. Also, the percentage of species that went extinct was smaller than you imply. It was far from "total sterilization". Insect species probably were not affected much at all. I think the only large extinction of insect species was the Permian-Triassic extinction event.

Name something over 2kg that survived that wasn't aquatic. That's the cutoff I've seen cited in a number of fairly knowledgeable discussions of the topic. Yes, AQUATIC reptiles of a larger size PERHAPS survived, BUT a small crocodile (say a hatchling) might well be your survivor in that case. As you say, they can eat little and often estivate. They grow slowly, so they would remain small and requiring less food for a substantial time period. Turtles are at least aquatic (and most such species are in the under 2kg range, or close to it) and many are ocean dwellers, thus much less affected.

As for insects, they exist is truly mind-blasting numbers. There are said to be something on the order of a billion ants for every hectare of land outside the arctic. 99.95% losses would be practically meaningless to those kinds of numbers in terms of SOME individuals surviving. They are also classic r-strategists, which would clearly be advantageous.

You should review the actual physical effects of the Chixulub event as well. Its actually pretty damned amazing that as much survived as did. The top 1 meter of the ENTIRE OCEAN was boiled away. The air temperature over the entire globe was raised to the flash point of dry organic material, and pelted with a rain of debris significant enough to leave several inches on average over the whole surface of the Earth. I don't see anything incompatible with the notion that 1 out every 2,000 rats managed to survive, and not much else. Again, if this was not so, then why NOT ONE SINGLE non-avian dinosaur? Surely some of them were small, adaptable, could eat seeds/nuts/insects/carrion/something. They just weren't quite as small and numerous as the mammals. 1 in 2000 of THEM wasn't enough.

I have seen a lot of things that indicate that it was not anywhere near as bad as you describe. In your original post, you give very specific numbers, such as 99.95%. We do not know how many creatures survived at all. That number is completely arbitrary. Even if we magically had such a number, it wouldn't be a useful number. The catastrophe obviously would have effected different species in different habitats very differently. Many obviously suffered 100% die off. Other creatures, we just don't know. Also, a large number of aquatic species did die out. The oceans were not spared.

As for "anything over 2 kg", that is a completely arbitrary number also. I don't think that an alligator would need to be small to have survived. There still would have been some food and they don't need to eat much. They are also not picky about what they eat; smaller alligators could have been on the menu along with just about any other creature. Maybe there was a platypus ancestor that weighed 3 kg that survived. I will name him Fred. There, I named one. Anyway, there was not some arbitrary weight limit. When you cut off photosynthesis for possibly years, what ecosystems are left? Basically ecosystems where the base of the ecosystem feeds on rotting plant material. This is essentially a swamp ecosystem or perhaps a very moist forest floor. Dry material doesn't support much invertebrate life. There still would have been insect larvae, worms, snails, slugs, and other invertebrates that feed on rotting plant material or the fungus that grows on them in swamp-like ecosystems.

So, what was selected for rather than selecting some arbitrary weight limit? The creatures that would still survive in these detritus based ecosystems would be insectivores and other generalist omnivores similar to rats that will eat just about anything. Any creatures dependent on active plant growth would die off. This would include herbivores, the predators that hunt them, the scavengers that scavenged them, and several other niches (egg eaters, etc). Were there any insectivore dinosaurs? Probably not. If there had been a larger termite eating dinosaur, then maybe it would have survived. Termites eat dead plant material; probably plenty of that around. Just about any dinosaur was too large to be an insectivore. Most insectivores are nocturnal, since most insects come out at night; dinosaurs are not thought to have been nocturnal either. Things were probably still very tough though, or some small dinosaurs would have survived by eating the small mammals, birds, amphibians, fish, and reptiles that did survive. I would suspect that the birds and mammals that survived were those that already hunted in such swamp-like ecosystems. Similar event happened in the oceans. Creatures that fed high in the water column and were dependent on active photosynthesis died out in large numbers, The bottom dwellers did okay since those ecosystems are based on detritus falling from above.

Also, for the time after the impact event, while insectivores and similar creatures were selected for, the very small ones may actually have been selected against. Even under normal conditions, very small mammals or birds (shrews or hummingbirds for example) live only a very short time away from starvation. With an uncertain food supply, such small size could have been detrimental. Also, temperatures could have been much colder than before. This also selects for larger creatures that do not have to expend so much energy to keep warm and can store more fat for lean times. Those that survived may have been around the equator; it may have been much to cold any places too far north or south. They could have grown larger very quickly as they spread back north to colder climates as plant life recovered.

You fall into the same "everything is possible" trap that a lot of people fall into when they want to argue against generalizations. You fail to see that generalizations are often a helpful tool and do not have to fit to 100% of cases to be an accurate description of reality.

If I say smoking is unhealthy, showing me a healthy smoker is no counter argument. It is an exception that proves the rules.

According to the fossil records pretty much nothing that was cat sized or over survived. While a lot of small animals survived instead. Obviously this doesn't hold as true for water based animals and there are exceptions. But for the mostly warm blooded land animals it seems to be true and explains why mammals made it and dinosaurs didn't. Seems to be a pretty good generalization. Being the underdogs and good at escaping hunting dinosaurs seems to have helped mammals.

 

[Alhazred]

DStaal[/url]":3tq6k9ri]
Hence my theory that the dinosaurs were probably starting to adapt to the rise of grass, but still preferred other plant sources. (As grasses weren't dominant anyway, most likely - they are the new kid on the block.) You get a worldwide cataclysm, and suddenly the fast-growing fast-spreading grasses are more common, but they aren't as good a food source for the large plant-eating dinosaurs.

Meanwhile they are just fine food sources for the small, seed-eating mammals: Their seeds aren't any harder to digest than other seeds. Adaptations to actually eat the grass can come later, when there isn't as much competition in that space.

Anyway, just a hypothesis, and I don't think it would be enough in and of itself to cause extinction, but I think it could be another small push for the mammals and against the dinosaurs. Some of this depends on when and how some specific features of grass evolved anyway - specifically their tough cell walls.

Yeah, its all just a mass of unknowns. We don't know the prevalence of different plants or even of different ecosystems, exactly how they were changing, how they looked after the K-Pg vs before, etc. That's the whole problem that all these theorists have, they really don't have sufficient evidence. They're working with a few scraps of material and trying to imagine what an entire world was like and what happened in it. Inevitably most of it is at least partially speculation.

 

[Alhazred]

Hat Monster[/url]":1kiaomlt]

Nostromo21[/url]":1kiaomlt]Has any of the science ever addressed why ocean-dwelling dinosaurs also died out at about the same time/rate as did the land-bound ones...? Surely the asteroid impact (pardon the pun!) would have been much less in the oceans...or am I missing something obvious...? :-/

There were no oceanic dinosaurs.

There were large marine reptiles like icthyosaurs, mosasaurs, plesiosaurs, pliosaurs, etc. They weren't dinosaurs, nor even particularly closely related to them. Their food chain collapsed too.

Did it? Fish weren't much affected. Ammonites seem to have been, but all throughout the last part of the Cretaceous, the Maastrichtian, ammonite groups were on the decline. Ichthyosaurs vanished quite a while before the End Cretaceous, and mosasaurs replaced them, then themselves went into decline. What's odd is that terrestrial reptiles were little affected, but aquatic ones were totally wiped out. There's a specific story for each group that survived or perished, I expect.

 

[Shavano]

JPan[/url]"b5b8ewm]
According to the fossil records pretty much nothing that was cat sized or over survived. While a lot of small animals survived instead. Obviously this doesn't hold as true for water based animals and there are exceptions. But for the mostly warm blooded land animals it seems to be true and explains why mammals made it and dinosaurs didn't. Seems to be a pretty good generalization. Being the underdogs and good at escaping hunting dinosaurs seems to have helped mammals.

No, it doesn't explain why dinosaurs didn't survive. The lightest non-avian dinosaurs were under a kilogram. The size thing only explains the extinction of their larger relatives.

 

[Shavano]

Alhazred[/url]":18iy4diy]

Hat Monster[/url]":18iy4diy]

Nostromo21[/url]":18iy4diy]Has any of the science ever addressed why ocean-dwelling dinosaurs also died out at about the same time/rate as did the land-bound ones...? Surely the asteroid impact (pardon the pun!) would have been much less in the oceans...or am I missing something obvious...? :-/

There were no oceanic dinosaurs.

There were large marine reptiles like icthyosaurs, mosasaurs, plesiosaurs, pliosaurs, etc. They weren't dinosaurs, nor even particularly closely related to them. Their food chain collapsed too.

Did it? Fish weren't much affected. Ammonites seem to have been, but all throughout the last part of the Cretaceous, the Maastrichtian, ammonite groups were on the decline. Ichthyosaurs vanished quite a while before the End Cretaceous, and mosasaurs replaced them, then themselves went into decline. What's odd is that terrestrial reptiles were little affected, but aquatic ones were totally wiped out. There's a specific story for each group that survived or perished, I expect.

Fish were significantly affected. Only 7 of the 41 cartilaginous fish families survived; almost all skate and ray species disappeared. Bony fishes did better. Many marine invertebrate families were also much affected. In general, those that lived in deep water were more likely to survive than those that lived at the shoreline. Among echinoderms, tropical and shallow-water species were most affected.

 

[Alhazred]

jimcox[/url]":djvhpra0]
I have seen a lot of things that indicate that it was not anywhere near as bad as you describe.

You'll need to be more specific.

In your original post, you give very specific numbers, such as 99.95%. We do not know how many creatures survived at all. That number is completely arbitrary. Even if we magically had such a number, it wouldn't be a useful number. The catastrophe obviously would have effected different species in different habitats very differently. Many obviously suffered 100% die off. Other creatures, we just don't know. Also, a large number of aquatic species did die out. The oceans were not spared.

I didn't say the 'oceans were spared', though the most profound effects seem to have been on terrestrial tetrapods. As for an 'arbitrary number', its a HYPOTHESIS, that's how it works, you look at the evidence and you form a hypothesis as to what that evidence means! Its NOT ARBITRARY, I provided a perfectly reasonably logic for it. In some sense it is of course just a guess, not some kind of exactly fixed number, so attacking it on the basis of 'arbitrariness' is wrong-headed, its just a number that stands for the hypothetical "most every individual perished." Nor is it meaningful to criticize the statement on the basis of it being 'universal'. Of course there was variation across both locale and species! However its not necessary that ANY species was 100% wiped out by the direct effects of the impact. Its quite likely many were done in by the 2nd and 3rd order effects over some period of time (however short in geological terms this still could have been several 1000 years at least).

As for "anything over 2 kg", that is a completely arbitrary number also. I don't think that an alligator would need to be small to have survived.

What you (or I) 'think' is irrelevant, only facts are relevant, go get facts. If large crocodillians survived, as individuals, then either there is or is not evidence of that. If there isn't then we can only speculate, if there is then present it. Unfortunately the only footnote about animal mass in the quote you provide is a dead link to a book, which presumably must have had its own citations. I can't find anything definitive that would favor your 25kg over my 2kg claim, so these must remain unsupported for the present.

There still would have been some food and they don't need to eat much. They are also not picky about what they eat; smaller alligators could have been on the menu along with just about any other creature. Maybe there was a platypus ancestor that weighed 3 kg that survived. I will name him Fred. There, I named one. Anyway, there was not some arbitrary weight limit.

It isn't about some ARBITRARY weight limit. Its about a question of what was the largest body mass of something that could have, and DID, survive? Again, you simply speculate and hypothesize, which is fine, but tie that to some theory at least! I've presented a theory, and shown how it would possibly mesh with observation. Its not 'proven' nor is it 'correct', it is simply a theory! Rhetoric is a meaningless response to that.

When you cut off photosynthesis for possibly years, what ecosystems are left? Basically ecosystems where the base of the ecosystem feeds on rotting plant material. This is essentially a swamp ecosystem or perhaps a very moist forest floor. Dry material doesn't support much invertebrate life. There still would have been insect larvae, worms, snails, slugs, and other invertebrates that feed on rotting plant material or the fungus that grows on them in swamp-like ecosystems.

Sure, nothing to disagree with here. I would point out that insect diversity seems to have taken about 1.7 million years to recover (as proxied by evidence of insect predation on plants). So even these basic detritivore ecosystems were probably far from unscathed.

So, what was selected for rather than selecting some arbitrary weight limit? The creatures that would still survive in these detritus based ecosystems would be insectivores and other generalist omnivores similar to rats that will eat just about anything. Any creatures dependent on active plant growth would die off. This would include herbivores, the predators that hunt them, the scavengers that scavenged them, and several other niches (egg eaters, etc). Were there any insectivore dinosaurs? Probably not. If there had been a larger termite eating dinosaur, then maybe it would have survived. Termites eat dead plant material; probably plenty of that around. Just about any dinosaur was too large to be an insectivore. Most insectivores are nocturnal, since most insects come out at night; dinosaurs are not thought to have been nocturnal either. Things were probably still very tough though, or some small dinosaurs would have survived by eating the small mammals, birds, amphibians, fish, and reptiles that did survive. I would suspect that the birds and mammals that survived were those that already hunted in such swamp-like ecosystems. Similar event happened in the oceans. Creatures that fed high in the water column and were dependent on active photosynthesis died out in large numbers, The bottom dwellers did okay since those ecosystems are based on detritus falling from above.

I don't know what this is all addressing really in terms of anything I've said. Its either just arbitrary speculation ( I have for instance no reason to believe that there were no insectivorous dinosaurs, though I'd note that these are exactly the sort of dinosaurs that probably DID survive, as birds are quite often insectivores).

Also, for the time after the impact event, while insectivores and similar creatures were selected for, the very small ones may actually have been selected against. Even under normal conditions, very small mammals or birds (shrews or hummingbirds for example) live only a very short time away from starvation. With an uncertain food supply, such small size could have been detrimental. Also, temperatures could have been much colder than before. This also selects for larger creatures that do not have to expend so much energy to keep warm and can store more fat for lean times. Those that survived may have been around the equator; it may have been much to cold any places too far north or south. They could have grown larger very quickly as they spread back north to colder climates as plant life recovered.

They might have been selected against LATER, perhaps, but this is all speculation. Its still quite possible they were what DID survive the actual event. Anything that didn't survive the actual event, its irrelevant what the selection pressures would have been on it later, it was dead. Also you should be careful when you extrapolate from MODERN birds and mammals to those of the earliest Paleogene, they would have been quite different in some respects. They may for instance have been more able to weather a lack of food. Nor is it exactly unknown for small animals to survive lean times, most rodents are quite good at this, and there's no reason to believe many early mammals would have been different. Likewise with birds. Nor does my hypothesis require that the smallest animals be the most favored. The hypothesis was only that small body size below some cutoff was required, was a gate, to survival. This would favor the most numerous creatures below that size. There could of course also be many other criteria for survival, including specific habitats, food requirements, etc. I didn't mention those so it would be incorrect to jump to the conclusion that I think they are irrelevant.

 

[JPan]

Shavano[/url]":wfkj5cxi]

JPan[/url]":wfkj5cxi]
According to the fossil records pretty much nothing that was cat sized or over survived. While a lot of small animals survived instead. Obviously this doesn't hold as true for water based animals and there are exceptions. But for the mostly warm blooded land animals it seems to be true and explains why mammals made it and dinosaurs didn't. Seems to be a pretty good generalization. Being the underdogs and good at escaping hunting dinosaurs seems to have helped mammals.

No, it doesn't explain why dinosaurs didn't survive. The lightest non-avian dinosaurs were under a kilogram. The size thing only explains the extinction of their larger relatives.

A kg is much much much more than the 1-200 gr that shrews to rats have. Also which of them did live at the end of the cretacious? All real dinosaurs were much larger than that. The only REALLY small dinosaurs seem to be predecessors of birds from the late jurassic/early cretacious. Which had been replaced by REAL birds at the end of the cretacious which seems to explain why they survived?

https://en.wikipedia.org/wiki/Anchiornis

 

[Luddite Curmudgeon]

Router66[/url]":1oob57bs]

On the evolution of grasses, take a look at this one. It was announced only last year and it effectively pushes the grass timeline some 40my back - at least.
http://www.sci-news.com/paleontology/sc ... 02482.html

Oooh, a stoned sauropod. The mind boggles!

 

[caldepen]

Isn't this sort of misleading? I was under the impression that most everything died out during that global event. Basically smaller versions of everything survived to repopulate and evolve, leaving what we have today, mammals, birds, fish and reptiles (not including insects and plants, etc.).

 

[DStaal]

caldepen[/url]":2ntmea0l]Isn't this sort of misleading? I was under the impression that most everything died out during that global event. Basically smaller versions of everything survived to repopulate and evolve, leaving what we have today, mammals, birds, fish and reptiles (not including insects and plants, etc.).

But why 'most'? And why did the most important group for the previous 200 million years (basically since the beginning of real land animals, and a period twice as long as mammals have dominated since) suddenly become a minor sideline? They'd survived everything else, why not this?

 

[Wickwrack]

Obligatory XKC

 

[caldepen]

DStaal[/url]":2ds4yrkb]

caldepen[/url]":2ds4yrkb]Isn't this sort of misleading? I was under the impression that most everything died out during that global event. Basically smaller versions of everything survived to repopulate and evolve, leaving what we have today, mammals, birds, fish and reptiles (not including insects and plants, etc.).

But why 'most'? And why did the most important group for the previous 200 million years (basically since the beginning of real land animals, and a period twice as long as mammals have dominated since) suddenly become a minor sideline? They'd survived everything else, why not this?

I am not sure they became a minor sideline at all (well until we came along anyway). Reptiles and birds continued to dominate along with mammals. All populations were hit and brought low and the world we see today (well 100 years ago), is a result of the recovery. The event just hit the reset button and leveled the playing field perhaps.

 

[llanitedave]

SixDegrees[/url]":34z2sx1e]

ViciousAndCruel[/url]":34z2sx1e]i think it also had to do with how quickly a species matured before having the next generation. Mice sized beasties are fast. Elephant sized Dino's probably not as much.

But a lot more very small dinosaurs died out along with their rarer, elephant-size brethren. And dinosaur development rates were, apparently, very fast, at least in many cases. It's an interesting idea, but I don't think it holds up very well to the data.

I really haven't been able to find anything in the literature that confirms that "very small dinosaurs" were common in the late Cretaceous. While I'm far from convinced that dinosaurs as a group were in decline towards the end of the Cretaceous, it does seem that Pterosaurs and the smallest non-avian dinosaurs had been largely replaced by birds and small mammals prior to the K-T event.

I could be wrong, but I can't seem to find any specifics to the contrary.

 

[Alhazred]

llanitedave[/url]":6x0ukh7f]

SixDegrees[/url]":6x0ukh7f]

ViciousAndCruel[/url]":6x0ukh7f]i think it also had to do with how quickly a species matured before having the next generation. Mice sized beasties are fast. Elephant sized Dino's probably not as much.

But a lot more very small dinosaurs died out along with their rarer, elephant-size brethren. And dinosaur development rates were, apparently, very fast, at least in many cases. It's an interesting idea, but I don't think it holds up very well to the data.

I really haven't been able to find anything in the literature that confirms that "very small dinosaurs" were common in the late Cretaceous. While I'm far from convinced that dinosaurs as a group were in decline towards the end of the Cretaceous, it does seem that Pterosaurs and the smallest non-avian dinosaurs had been largely replaced by birds and small mammals prior to the K-T event.

I could be wrong, but I can't seem to find any specifics to the contrary.

OTOH I've never seen anything that indicated there was some sort of decimation of small dinosaurs prior to the K-Pg either. In fact the long term trend in groups closely related to the avian lineage was for smaller size from what I've heard. So its likely there were a whole variety of bird-like small dinosaurs. Mammals seem to have diversified a good bit in the later Cretaceous, but that also may be an illusion in that a bunch of groups, which had diversified in that period, survived, but many other groups stemming from earlier rounds of diversification perished. So its not clear there was increased diversification going on there. Certainly there was no notable trend towards larger body size or movement out of the classic Mesozoic mammal niches.

 

[rmgoat]

d0x[/url]":1umtm0nf]

Torbjörn Larsson, OM[/url]":1umtm0nf]Mammals are just lucky, they didn't need a wish bone.

Fatesrider, a recent article claims the scene was set before brooding. Avian dinosaurs had beaks and were specialized on seeds. Buried seeds would have sustained them until the plants grew back. That would explain why non-beaked avian analogs among dinosaurs didn't make it. YMMV of course.

Today seems to be nitpick time:

This dark period of die-outs is called the K-T mass extinction,

More correct today is the Cretaceous-Paleogene, K-Pg or perhaps better K/Pg (?) boundary, the two former which the press release uses. [Thanks, Keysh!]

And it wasn't lack of smarts either, because winged dinosaurs (aka birds) didn't manage to out-compete mammals, despite their intelligence.

Birds did out-compete mammals. There are ~ 10,000 avian species, but just ~ 6,000 mammalian species.

Which takes me to this:

Keysh[/url]":1umtm0nf]
Their "counterparts among the Dinosauria" did not recover at all, because they were all extinct.

I am willing to bet some surviving mammals were seed eaters as well, even if tubers would be a better survival diet.

Well we can still even the odds and get rid of some birds. Ones like pigeons and seagulls have my vote. Sure sure eco system and all but can we at least kill the seagulls? I don't live anywhere near the damn ocean and I see them

The domestic cat (Latin: Felis catus) seems well on it's way to reducing the number of bird species. Unfortunately for you they are unlikely to make much impact on the species you named.

 

[rmgoat]

JPan[/url]":k6ppw03l]

SixDegrees[/url]":k6ppw03l]

ViciousAndCruel[/url]":k6ppw03l]i think it also had to do with how quickly a species matured before having the next generation. Mice sized beasties are fast. Elephant sized Dino's probably not as much.

But a lot more very small dinosaurs died out along with their rarer, elephant-size brethren. And dinosaur development rates were, apparently, very fast, at least in many cases. It's an interesting idea, but I don't think it holds up very well to the data.

Mammals were rat sized, dinos at best cat sized. Huge difference. Ask an Australian if its possible to exterminate dogs from an island and the answer is most likely yes, cats and the answer is "with a lot of effort". Rats and the answer is "forget about it".
I don't think there is much more need for explanations of what happened.

There are no rats in Alberta, a Canadian province for those that don't know. They are fortunate in that they have only two rat friendly borders with part of Montana and Saskatchewan to defend. The Rocky mountains are a good barrier to the west and the northern border is also very rat unfriendly as is the northern half of the Saskatchewan border. $350,000 Cdn annually, taxpayers money well spent.

Saskatchewan doesn’t have a rat patrol, but the province has stepped up its rat control effort in recent years. Two-thirds of its regional municipalities are now rat-free and the province could be entirely rat-free within a decade.

Contrary to your belief several islands have had rats eradicated, see the link below.

http://www.theverge.com/2015/5/13/85928 ... radication

 

[iEvolution2]

rmgoat[/url]":147secro]

JPan[/url]":147secro]

SixDegrees[/url]":147secro]

ViciousAndCruel[/url]":147secro]i think it also had to do with how quickly a species matured before having the next generation. Mice sized beasties are fast. Elephant sized Dino's probably not as much.

But a lot more very small dinosaurs died out along with their rarer, elephant-size brethren. And dinosaur development rates were, apparently, very fast, at least in many cases. It's an interesting idea, but I don't think it holds up very well to the data.

Mammals were rat sized, dinos at best cat sized. Huge difference. Ask an Australian if its possible to exterminate dogs from an island and the answer is most likely yes, cats and the answer is "with a lot of effort". Rats and the answer is "forget about it".
I don't think there is much more need for explanations of what happened.

There are no rats in Alberta, a Canadian province for those that don't know. They are fortunate in that they have only two rat friendly borders with part of Montana and Saskatchewan to defend. The Rocky mountains are a good barrier to the west and the northern border is also very rat unfriendly as is the northern half of the Saskatchewan border. $350,000 Cdn annually, taxpayers money well spent.

Saskatchewan doesn’t have a rat patrol, but the province has stepped up its rat control effort in recent years. Two-thirds of its regional municipalities are now rat-free and the province could be entirely rat-free within a decade.

Contrary to your belief several islands have had rats eradicated, see the link below.

http://www.theverge.com/2015/5/13/85928 ... radication

Rats in that region might have evolved into something else. See that little thing running around? Look carefully, it is a rat.

 

[ackmondual]

ZenBeam[/url]":2lw6j1lv]"But the researchers found that after the asteroid impact, several mammal species rapidly evolved to be quite large. So obviously it wasn't size alone that killed off the dinosaurs."

That doesn't follow. Enough food to support large mammals 200,000 years after impact, or even 100 years after impact, doesn't help the large dinosaurs who need food immediately after impact.

I never got this either. Perhaps there was still food, but not enough to sustain the large numbers of living beings at the time.

 

[Bart _Dale]

Having read the reviews, i would like to point out a few things.

1. While there were "small dinosaurs", small is a relative term. There were no dinosaurs I am aware of as small as a mouse or rat. I haven't see any evidence for dinosaurs as small as 1 kg (2.2 lbs).

2. Unlike birds, many species of mammals, even large mammals, under go hibernation. Hibernation would allow mammals to ride out a period of ecological disaster caused by a giant meteor strike. Many reptiles and amphibians can also under go extended period of inactivity. (Definition of hibernation was revised to include bears.)

Birds, with very few exceptions, do not undergo extended periods of inactivity (hibernation). If dinosaurs were like birds they too might not have been able to hibernate, so even small dinosaurs could be be hit hard by the massive meteorite strike. After a few months, plants might recovery, but dinosaurs it appear had high bird like metabolisms, but possibly no ability to undergo hibernation, and would starve to death, even small dinosaurs.

3. Birds greater mobility would allow them to find the few spots where the environment might have been spared, a sheltered valley or such, which allow them to survive. Even so, birds did not survive as well as mammals - only a few families of birds survived, some of them based on aquatic or seabird bird families.

4. Mammals survived better. The groups of mammals that survived were from much more widely diverse groups, Placental, Marsupial, Monotremes, and Multitubulars. The bird survival is more as if one family of mammals had survived, say Primates, and only certain branches of it at that.

5. Crocodiles are large, but aquatic, and in any case they can "aestivate" (their equivalent of hibernation).

6.Even if the absolute number of dinosaur species decline fore the K-T extinction, dinosaurs were a long, long way from becoming extinct. if not as common as they once were (and that is highly debatable), dinosaurs were still common and numerous overall up to the time of the extinction. Had the K-T extinction not occurred, presumably due the giant meteorite impact, there is no indication that the dinosaurs would have disappeared anyways in the next few million years, the fossil record doesn't support that.