Thread: "Why did the dinosaurs die out?"

I hear this question a lot, and, as far as I've heard, there hasn't really been a concise agreement as to why. But I recall hearing the other day that there was once a much larger amount of carbon dioxide in the atmosphere (around the time of the dinosaurs). This meant that plants were everywhere, and thus the primarily herbivirous dinos were able to grow to ultimately unnecessary sizes because food was so extraordinarily plentiful. Since there is less carbon dioxide in the air nowadays—and I'm assuming that the shift happened somewhere near the end of the dinosaurs, correct me if I'm wrong—there are less plants, so giant reptillians can no longer exist as they once did.

One theory: The Alvarez Hypothesis.

The Alvarez hypothesis posits that the mass extinction of the dinosaurs and many other living things was caused by the impact of a large asteroid on the Earth sixty-five million years ago, called the Cretaceous–Paleogene extinction event. Evidence indicates that the asteroid fell in the Yucatán Peninsula, at Chicxulub, Mexico. The hypothesis is named after the father-and-son team of scientists Luis and Walter Alvarez, who first suggested it in 1980. In March 2010 an international panel of scientists endorsed the asteroid hypothesis, specifically the Chicxulub impact, as being the cause of the extinction. A team of 41 scientists reviewed 20 years of scientific literature and in so doing also ruled out other theories such as massive volcanism. They had determined that a 10–15 km (6–9 mi) space rock hurtled into earth at Chicxulub. The rock's size could be approximately the entire size of Martian moon Deimos (mean radius 6.2 km); the collision would have released the same energy as 100 teratonnes of TNT (420 ZJ), over a billion times the energy of the atomic bombs dropped on Hiroshima and Nagasaki.^[1]

Alvarez hypothesis - Wikipedia, the free encyclopedia

There is no serious disputing of the asteroidal impact theory of dinosaurian extinction. Exactly what machinism of the extinction event was most devastation to dinos, and not to mouselike mammals or flying birds, we do not know.
Mind you that this was only one of many "extinction events" in the history of our world.

There could also have been a virus that was caused by or indirectly, the asteroid collision, that might also have been attributed to the extinction of them.

Every thread should have the relevant xkcd link:
xkcd: Birds and Dinosaurs

Originally Posted by Strange

Every thread should have the relevant xkcd link:
xkcd: Birds and Dinosaurs

You beat me to saying that they didn't actually die out.

Hey! But if the dinosaurs evolved into birds and so there are no dinosaurs around any more ... how come we evolved from monkeys but there are still monkeys around !?!!1!?

Originally Posted by Strange

Hey! But if the dinosaurs evolved into birds and so there are no dinosaurs around any more ... how come we evolved from monkeys but there are still monkeys around !?!!1!?

Hey no fair! The birds have 65 million years to wipe out the dinosaurs, while humans have only had a few hundred thousand to wipe out the monkeys, but we've made excellent progress the past few decades towards that end. :-) (j/k)
--
Asteroid and related ecological disaster has good evidence and is the leading hypothesis by a long shot.

Exactly what machinism of the extinction event was most devastation to dinos, and not to mouselike mammals or flying birds, we do not know.
Mind you that this was only one of many "extinction events" in the history of our world.

There was a neat hypothesis advanced - but in a tv documentary series, I haven't tracked down any citations. Because it was about Australia we, of course, spent a lot of time on the monotremes, platypus and echidna. The view about mammals at the time of that extinction event was that there might have been several or many larger species around when dinosaurs were, but the asteroid impact itself meant that smaller creatures with a burrowing habit would have been better sheltered from that. So the larger ones were eliminated (if they were there at all).

The presenter also referred to some reptiles as survivors and showed that the ones which survived not only were shielded from the explosion effects, they also had feeding habits and slow metabolic rates that allowed them to survive in the early years following that impact. Animal prey had been largely wiped out and vegetation was severely limited by the dust clouds blocking sunlight. A creature that needed little nourishment and could survive long periods with none at all was in a distinctly advantageous position. Some of the mammal survivors had habits we might call hibernation - which was really more like, too little food, don't waste energy looking for food that isn't there and sleep a lot.

Alternately, Torres and the guys at arecibo have something else to add to the discussion.
Habitability of the Paleo-Earth as a Model for Earth-like Exoplanets - Planetary Habitability Laboratory @ UPR Arecibo

Our analysis shows that terrestrial habitability has been greater than today for most of the Phanerozoic as demonstrated by both habitability metrics, RVD and SPH (Figure 5). This makes sense with the fossil record as it is known that life was more abundant during many previous periods and were disturbed by extinction events. Today's terrestrial habitability (SPH) is about 0.6 but it was particularly more habitable during the Devonian (SPH > 0.9) and from the Triassic to the Cretaceous (SPH > 0.7). As expected, a more habitable planet (higher productivity) can support a larger biota (i.e. Dinosaurs). The RVD and SPH are generally correlated after 350 Ma when plants were more common, but there is a notable divergence between 280 Ma to 180 Ma. Both the RVD and SPH show a marked decrease on terrestrial habitability in the last 100 million years.
Luckily, Earth stayed as a mesoplanet during all the Phanerozoic, something that was crucial for the evolution of complex life. Future observations of Earth-like exoplanets may be put in context with the evolution of terrestrial habitability. More analysis will include correlations with the fossil record and other parameters. There are three big questions that need to be answered. First, why terrestrial habitability has been decreasing in the last 100 million years? (if related, the K-Pg mass extinctions was 65 million years ago).

Coupled with other claims I've read on the subject, which talk about a slow diminishment of species diversity, or a long period of decrease/demise leading up to the final "extinction event"
Assuming that the dinasaurs evolved to take advantage of a richer environment with higher temperatures, higher atmospheric density--more Oxygen, more co2, more water vapor, as these declined, so did the dinasaurs, weakened by a decline in habitability and temperature, their tolerance for stress was weakened too.

Because they had a big head and little arms.

The fliers, for obvious reasons can get out of harms way or find resources more easily than slow ground creatures--we see this even in today's largest forest fires for example.

Not sure about hibernation--though it makes sense--I wonder whether there's evidence for hibernation in early mammals.

I do not think that ALL of the dinosaurs went extinct, perhaps over 80 or 90 percent but there were some who survived.

I wonder whether there's evidence for hibernation in early mammals.

There was certainly some discussion along those lines in the series I was talking about. But it was just one among several strategies. The presenter also referred to the kangaroo process of insemination and pregnancy being delayed/separated. The foetus doesn't begin to develop straight away, the mother's system needs to give a signal that now is the time. Very handy in a resource constrained environment. Mate whenever healthy partners are available but only start gestation when there's enough food to sustain mother, foetus and suckling joey. Similar effect on survival to animals that only need to eat rarely.

strange that no-one has mentioned the Deccan flood basalts - surely that would have put plenty of environmental stress on the ecosystems, which an asteroid impact would only have made worse

But the Deccan traps were doing their thing both before and after the asteroid impact. That steady increase in CO2 would have had a warming effect (much, much slower than what we're doing now) but very little in the way of a years long global blanketing dust storm which would have followed the asteroid impact. That was really the killer.

The traps were smoking away for more than 5 million years. The asteroid impact was initially massive for a day or two - but the dust cloud would have lasted for a few years and more or less blotted out the sun entirely for the first year or two. Not at all conducive to growing the vegetation animals need to feed on.

Robert Sloan has listed the percentage of oxygen in samples of dinosaur-era amber as: 28% (130m years ago), 29% (115m years ago), 35% (95m years ago), 33% (88m years ago), 35% (75m years ago), 35% (70m years ago), 35% (68m years ago), 31% (65.2m years ago), and 29% (65m years ago).

High ambient oxygen and the K/T boundary extinctions

65 million years ago (MyBP) mass disappearances of some 70% of all biotic species, delineated the Cretaceous‐Tertiary (K/T) boundary (Hallam and Wignall, 1997). Alvarez et al. proposed that the causal agent was a climatic cataclysm, resulting from the impact of a bolide (Alvarez et al., 1980). This has now been widely accepted (Macleod and Keller, 1996). However, one conundrum remains: the decline of certain flora and fauna species which commenced some ten million years before the K/T event (Sloan et al., 1986; Johnson and Hickey, 1990; Sweet et al., 1990; Johnson, 1993; Macleod et al., 1997). These and other findings have suggested more gradually developing biosphere degrading factors, such as extreme volcanism

We seem to tend to want to find One answer for complexities. Sometimes, (especially when we set the rules) we can actually find that one answer.
But--that ain't most of the time. A drop in oxygen levels from 35%(68mybp) to 29%(65mybp) may have stressed the larger animals much more then the smaller. Add in the dieoff of much of certain flora---maybe important for certain dining habits?

My pet theory could be termed "egg crisis". This is going by the evolutionary record, not climate. I propose that offspring mortality, by predation from new kinds of ovivores, was a major cause of extinction. Remember that the revolutionary adaptation of reptiles in the first place was their leathery not gelatinous eggs, that could be deposited safely on land; these first reptiles like modern crocs and turtles would crawl back into the water when hatched. I think the game has always been about offspring survival. Enter the mammal, a nightmare egg-eater. It digs and gnaws. Its hot blood makes it active when reptiles are most sluggish, and it's too small and fast for mothers guarding their clutches to combat. See how a mere rat can "take down" the t-rex, by chewing holes through all her eggs? Dinosaurs responded to the egg crisis by becoming smaller and faster, by laying hard-shelled eggs resistant to biting, and by nesting off the ground in cliffs and trees. Perversely, many small dinosaurs also developed nest-raiding capabilities, like piercing beaks or the ability to swoop down on unguarded clutches. This extinction theory, unlike others, also covers the marine dinosaurs because their eggs, also deposited on land or dug into sand, were just as vulnerable.

I think they developed cults and all committed suicide thinking that their creators were going to come take them back to their home planet if they shed their earthly bodies.

but then most of their brains were too small to be THAT stupid.

Originally Posted by Pong

My pet theory could be termed "egg crisis". This is going by the evolutionary record, not climate. I propose that offspring mortality, by predation from new kinds of ovivores, was a major cause of extinction. Remember that the revolutionary adaptation of reptiles in the first place was their leathery not gelatinous eggs, that could be deposited safely on land; these first reptiles like modern crocs and turtles would crawl back into the water when hatched. I think the game has always been about offspring survival. Enter the mammal, a nightmare egg-eater. It digs and gnaws. Its hot blood makes it active when reptiles are most sluggish, and it's too small and fast for mothers guarding their clutches to combat. See how a mere rat can "take down" the t-rex, by chewing holes through all her eggs? Dinosaurs responded to the egg crisis by becoming smaller and faster, by laying hard-shelled eggs resistant to biting, and by nesting off the ground in cliffs and trees. Perversely, many small dinosaurs also developed nest-raiding capabilities, like piercing beaks or the ability to swoop down on unguarded clutches. This extinction theory, unlike others, also covers the marine dinosaurs because their eggs, also deposited on land or dug into sand, were just as vulnerable.

It's not a theory. Theory is supported by evidence.
You point out 'hot blooded mammals' as if to imply that dinosaurs were disadvantaged by being cold blooded. This is a bit like saying that dolphins were disadvantaged in the seas by being cold blooded and having nowhere to lay their eggs.

Not to mention the very long standing presence of Oviraptors.

I repeat it's a pet theory, meaning personal speculation and admittedly wild.

I don't understand your issue with the advantage of warm bloodedness. It allows unsuppressed activity at night, and in winter. We're still assuming early mammals had a higher metabolism than their contemporary dinos, especially the ones died off, right?

Oviraptor may be a mistaken name, because the original site now appears to be oviraptor eggs, with brooding female oviraptor. So the name still works but in another way.

The first dinosaur feathers (oviraptor is thought to be lightly feathered) were around the crotch and forelimbs, so that in brooding posture they presented a fan around the eggs. While the obvious explanation is thermal, they may have been defensive also as feathers may act like a cat's whiskers to detect nest invaders. Anyway, they're perfect objects of sexual selection and so often evolve far beyond original utility - I don't put much stock in apparent function of any feathers.

Originally Posted by Pong

I repeat it's a pet theory, meaning personal speculation and admittedly wild.

It's Ping, Pong.

Originally Posted by Neverfly

It's not a theory. Theory is supported by evidence.
You point out 'hot blooded mammals' as if to imply that dinosaurs were disadvantaged by being cold blooded. This is a bit like saying that dolphins were disadvantaged in the seas by being cold blooded and having nowhere to lay their eggs.

Not to mention the very long standing presence of Oviraptors.

Oviraptor and its relatives were insectavors/herbivores, the original fossil form which the egg-stealing was based has been reexamined and shown to be a brooding female on her own nest.

Originally Posted by Pong

I repeat it's a pet theory, meaning personal speculation and admittedly wild.

I don't understand your issue with the advantage of warm bloodedness. It allows unsuppressed activity at night, and in winter. We're still assuming early mammals had a higher metabolism than their contemporary dinos, especially the ones died off, right?

Oviraptor may be a mistaken name, because the original site now appears to be oviraptor eggs, with brooding female oviraptor. So the name still works but in another way.

The first dinosaur feathers (oviraptor is thought to be lightly feathered) were around the crotch and forelimbs, so that in brooding posture they presented a fan around the eggs. While the obvious explanation is thermal, they may have been defensive also as feathers may act like a cat's whiskers to detect nest invaders. Anyway, they're perfect objects of sexual selection and so often evolve far beyond original utility - I don't put much stock in apparent function of any feathers.

Most if not all dinosaurs are now thought to have been warmblooded too, so the warm bloods beat out cold bloods is not a viable hypothesis (not "theory")

Originally Posted by Paleoichneum

Oviraptor and its relatives were insectavors/herbivores, the original fossil form which the egg-stealing was based has been reexamined and shown to be a brooding female on her own nest.

Ah, I looked it up. I was under the impression that there were many "oviraptors" and not a singles species. I found a page on that, here:
Oviraptoridae - the Oviraptors - the Egg Snatchers or Egg Robbers

Color me corrected on that point.

Originally Posted by Paleoichneum

Most if not all dinosaurs are now thought to have been warmblooded too, so the warm bloods beat out cold bloods is not a viable hypothesis (not "theory")

I thought blood temperature more a matter of degree than true/false. Crudely, I imagined a warm-bloodedness scale with the largest dinos at one end and smallest mammals at the other.


And, yes guys I get the distinction between theory and hypothesis. I make no pretensions about "my pet theory".

It is a matter of degrees, and the growth structuring seen in bone sectioning taken from many different genera all display the same patterning as seen in birds. this they had a comparable "warm-bloodedness"

Well, they had fur and are thought to be generally nocturnal. I'm gonna hold that mammals were more active than larger dinosaurs at night. Couple this with the most successful mammals being ratlike carnivorous burrowers with keen smell, why wouldn't eggs be a juicy target? Even with a staple diet of cockroaches and termites the opportunity to sap large egg clutches is unavoidable.

Terrestrial ovivores are uncommon today, and I see it's the last guess people make about an extinct animal's eating habit. By my hypothesis, that's because Mesozoic evolution was largely about resolving the problem of offspring predation. The survivors had all adapted effective means of protecting their young, so nest-raiding became less viable.

Originally Posted by Pong

Well, they had fur and are thought to be generally nocturnal. I'm gonna hold that mammals were more active than larger dinosaurs at night. Couple this with the most successful mammals being ratlike carnivorous burrowers with keen smell, why wouldn't eggs be a juicy target? Even with a staple diet of cockroaches and termites the opportunity to sap large egg clutches is unavoidable.

Logical. But it's been shown that many species of dinosaur did brood and guard eggs. They way I see this one, You would have to have massive armies of ovivores flowing in droves over the lands to get the result you're looking for.
Is that really plausible?

I should not have called this a cause of extinctions. It's a stress. That makes it more a driver of selection than a cause of extinction.

Though when a cataclysm like K–Pg wipes out 75% of species, the stressed ones are unlikely to survive.


A brooding dinosaur can't effectively rid her nest of creatures the size of rats and mice, unless she's smaller and faster than ...well, we know from experience: than a human. She can sit up all night turning her eggs? She can't bite at the vermin because that may puncture her soft eggs. The only way a larger animal can safely eradicate vermin amongst its eggs is by plucking them out with a tapered snout, like a beak.

Judging by modern freshwater crocodiles, egg predation was a huge problem. Despite the mothers' efforts to protect them, more than 80% of nests are destroyed by predators, with less than 1% of crocs living to maturity. It doesn't take a massive army of ovivores to seriously impact these large reptiles. Sea turtles have the same problem, mainly from dogs, raccoons, and other scavengers digging into their egg clutches. And that's today, when such nests are too rare for raiding them to be a worthwhile specialty of any species.


My main point is that adaptations leading up to the big extinction make more sense if we think the era as "about" resolving the problem of offspring predation.

Originally Posted by Pong

A brooding dinosaur can't effectively rid her nest of creatures the size of rats and mice, unless she's smaller and faster than ...well, we know from experience: than a human.

This is speculative... how do you know what a dinosaur could effectively do?

Originally Posted by Pong

The only way a larger animal can safely eradicate vermin amongst its eggs is by plucking them out with a tapered snout, like a beak.

Humoring- some had those. Or nearly.

Originally Posted by Pong

Judging by modern freshwater crocodiles, egg predation was a huge problem. Despite the mothers' efforts to protect them, more than 80% of nests are destroyed by predators, with less than 1% of crocs living to maturity.

Crocodiles are cold blooded reptiles and sluggish as well as massive (point- they can be very quick in short bursts but not sustained). Quite the contrast to a nimble and warm blooded mother animal.

Originally Posted by Pong

It doesn't take a massive army of ovivores to seriously impact these large reptiles.

How stressed are these crocodiles? Threatened? Endangered? Critical? Call a priest?

Originally Posted by Pong

And that's today, when such nests are too rare for raiding them to be a worthwhile specialty of any species.

Speculative, again. We don't really know enough about 240 million years ago to 65 million years ago to have a full picture of habitats and extensive diversity across the globe in those eras.

Originally Posted by Neverfly

Originally Posted by Pong

A brooding dinosaur can't effectively rid her nest of creatures the size of rats and mice, unless she's smaller and faster than ...well, we know from experience: than a human.

This is speculative... how do you know what a dinosaur could effectively do?

Apart from weird exceptions, like anteaters, an animal can't effectively combat something well outside its size range. And human vs. mouse is good evidence. An elephant confronted by a mouse, backs away.

Here its worth noting that dinosaur eggs have an upper size limit, regardless of how large the adult is, because a very thick membrane suffocates the embryo. Massive dinosaurs had relatively small eggs, and puny hatchlings that start life competing on a completely different scale than their parents.

Originally Posted by Neverfly

Originally Posted by Pong

The only way a larger animal can safely eradicate vermin amongst its eggs is by plucking them out with a tapered snout, like a beak.

Humoring- some had those. Or nearly.

Yes. The adaptation helps it protect the eggs.

Originally Posted by Neverfly

Originally Posted by Pong

Judging by modern freshwater crocodiles, egg predation was a huge problem. Despite the mothers' efforts to protect them, more than 80% of nests are destroyed by predators, with less than 1% of crocs living to maturity.

Crocodiles are cold blooded reptiles and sluggish as well as massive (point- they can be very quick in short bursts but not sustained). Quite the contrast to a nimble and warm blooded mother animal.

Yes. Warmer blood and nimbleness help dinosaurs protect the eggs.

Originally Posted by Neverfly

Originally Posted by Pong

It doesn't take a massive army of ovivores to seriously impact these large reptiles.

How stressed are these crocodiles? Threatened? Endangered? Critical? Call a priest?

I dunno, but 80% of nests destroyed is pressure alright. If crocs can adapt a means of decreasing that, it's a selective pressure. I reckon they can't. I reckon any changes to the croc would make it less successful in other ways.

Originally Posted by Neverfly

Originally Posted by Pong

And that's today, when such nests are too rare for raiding them to be a worthwhile specialty of any species.

Speculative, again. We don't really know enough about 240 million years ago to 65 million years ago to have a full picture of habitats and extensive diversity across the globe in those eras.

We know there were more dinosaur eggs than today.

aren't crocs one of the few animals that have been around since the time of the dinosaurs? if egg predation where that big a deal, how would they last so much longer than many other species?

Originally Posted by Pong

Apart from weird exceptions, like anteaters, an animal can't effectively combat something well outside its size range.

Nonsense. I've watched coyotes and wolves pounce at the ground and snap up mice like little snacks. They do it very adeptly.

Originally Posted by Pong

And human vs. mouse is good evidence.

If so, so is coyote and mouse.
So there you go- it isn't evidence of how an entirely different animal that existed 80 million years ago would have fared against shrew like mammals.

Originally Posted by Pong

An elephant confronted by a mouse, backs away.

I speculate that this is to avoid a mess on their foot, not a lack of desire to combat the mouse. Elephants are well documented in paying very close attention to where they step and to avoid stepping on any animal underfoot including humans and mice alike.

Originally Posted by Pong

Here its worth noting that dinosaur eggs have an upper size limit, regardless of how large the adult is, because a very thick membrane suffocates the embryo. Massive dinosaurs had relatively small eggs, and puny hatchlings that start life competing on a completely different scale than their parents.

There is evidence of nurturing parental behavior- even in the famous T. Rex.
In which case the competition on different scales means jack squat. I am honestly uncertain how much of that is speculative and how much actual supportive evidence there is. But in speculation vs. speculation- neither of us wins the round.

Originally Posted by Pong

Yes. The adaptation helps it protect the eggs.
Yes. Warmer blood and nimbleness help dinosaurs protect the eggs.

How do these support your stressed hatching hypothesis?

Originally Posted by Pong

I dunno,

I suggest that you find out. It's relevant.

Originally Posted by Pong

We know there were more dinosaur eggs than today.

True.
But we don't know how much stress those chain smoking lil buggers were under.

Pong, why are you comparing to crocodiles??? Compare to various bird species, as they are much closer to dinosaurs then the crocodyloids are. Also how exactly would a shew size mammal predate a ceratopsian, hadrosauroid or theropod egg in the first place? The size difference and shell thickness would have been prohibitive.

I have to admit, never having had the normal childhood fascination with dinos that it seems most children do, for too many years I thought all dinos lived at the same time. It has only been in the last 15 years that I understood the idea behind Jurassic, Triassic, Pleistocene, Eocene, and various other era names meant. Maybe pong is working on the same set of thrusters I was for a long time. Understanding the differences between the fauna of each era would give more indications of why each era of life went extinct. Wouldn't it?

@Neverfly. Coyote vs. mouse is good counterpoint. I especially like that for purpose of this argument coyotes have roughly similar capabilities to the reptiles I want to pressure, especially their jaws and teeth.

So if a surly dinosaur can gobble up small invaders, what about herbivores? If only herbivores were pressured by egg-eaters, only they'd get the adaptations I say are really about offspring protection. This is falsifiable... and untrue. (The list, just to refresh: live birth, hard eggshell, pointed snout or beak, remote nesting, smaller size, warmer blood.)

About nurturing behaviour. All mammals necessarily nurture their young; reptiles might. In modern species the contrast between reptilian and mammalian parenting is stark. Those Australian crocodiles mentioned above for example are notably incompetent at guarding their nests, what's more they accidentally stomp or rip their own eggs. They're about as purposeful as a cat instinctively brushing the kitty litter without burying anything. The surviving hatchlings just scatter, and hope they don't get cannibalized. To us mammals such parental ineptitude is almost unbelievable. And the sea turtle and probably most extinct marine reptiles return to the water after depositing their eggs to chance. So in absence of evidence we should assume dinosaurs besides the paravians were no better parents than contemporary reptiles. That's not "speculation vs. speculation".

Paleoichneum, it's logical to suppose dinos that evolved into birds were somewhat birdlike in their parenting behaviour. I'm sorry we've no better living examples than crocodiles, or maybe komodo dragons? to see how large reptiles topping the food chain would interact with other animals. Anyway I initially brought up crocodiles to show how dinosaurs are an improvement in context of this era-long struggle against egg predation I'm pushing.

Originally Posted by Paleoichneum

how exactly would a shew size mammal predate a ceratopsian, hadrosauroid or theropod egg in the first place? The size difference and shell thickness would have been prohibitive.

Hard shells are a cretacius development, after - maybe in response to - mammals. The rat teeth some of those early mammals had could certainly chew through a meat-filled football, and no egg was ever so tough as that - the embryo must have oxygen and must also break out eventually. But let's not lay all the blame on mammals. Presumably any carnivorous reptile will opportunistically eat eggs.

Originally Posted by Neverfly

Originally Posted by Pong

Yes. The adaptation helps it protect the eggs.
Yes. Warmer blood and nimbleness help dinosaurs protect the eggs.

How do these support your stressed hatching hypothesis?

I don't know what the "stressed hatching hypothesis" is, but here is my main point:

Originally Posted by Pong

Mesozoic evolution was largely about resolving the problem of offspring predation.

You've kinda co-argued that the more birdlike dinosaurs would have better egg survival ...I think that's done.
We haven't argued if mammals have any advantages for offspring protection. Wanna do mammals next?


@seagypsy. Thanks for your concern, but I'm running great on all three cylinders.

If mice were your only source of protein, you might become a very adept mouse-catcher.

Pong: what is the source of your assertion that calcified eggs are a Cretaceous development? Jurassic sauropod eggs were up to 5mm thick, had a microcrystaline structure and were notably hardened.

and birds are the better concept for egg care overall, as they are much closer in relation to dinosaurs then any of the Crocodylomorphs are.

Originally Posted by Pong

@seagypsy. Thanks for your concern, but I'm running great on all three cylinders.

LOL, that wasn't intended as an insult and I hope you didn't take it that way. It's just a common misunderstanding that laypersons seem to have about dinosaurs. I don't know what your level of study is in paleontology. Mine is zilch.

Sometimes the experts need to know what misconceptions you may hold in order to explain better where the disconnect is. So it was merely a suggestion that you could confirm or deny in order to help.

Originally Posted by Paleoichneum

Pong: what is the source of your assertion that calcified eggs are a Cretaceous development? Jurassic sauropod eggs were up to 5mm thick, had a microcrystaline structure and were notably hardened.

I'd thought they appeared in the mid or late mesozoic, then googled a few confirmations for this debate, yielding cretacious. Let's say jurassic for sake of argument: this supports my hypothesis that the Mesozoic was a time of evolutionary struggle to protect offspring.

Originally Posted by Paleoichneum

birds are the better concept for egg care overall, as they are much closer in relation to dinosaurs then any of the Crocodylomorphs are.

That's an exciting and trendy debate in itself: how birdlike in behaviour were the dinosaurs? which dinosaurs? did sauropods behave more like birds ...or elephants?

But I'm saying: more birdlike means better offspring survival. The crocodile is a living example of poor parenting. Are you trying to argue against my hypothesis or not?



For the record (seagypsy) I'll submit that I don't know enough, or what I do know is broken, or both. I have ideas, I have an internet connection, I try to be intellectually honest.

The crocodile is a living example of poor parenting.

Are you kidding? They've survived for 10s of millions of years. Maybe when our remote descendants have managed to do the same they might be able to make such observations. But we're in no position to do so. We haven't yet proven ourselves that successful.

Originally Posted by Pong

Originally Posted by Paleoichneum

Pong: what is the source of your assertion that calcified eggs are a Cretaceous development? Jurassic sauropod eggs were up to 5mm thick, had a microcrystaline structure and were notably hardened.

I'd thought they appeared in the mid or late mesozoic, then googled a few confirmations for this debate, yielding cretacious. Let's say jurassic for sake of argument: this supports my hypothesis that the Mesozoic was a time of evolutionary struggle to protect offspring.

Originally Posted by Paleoichneum

birds are the better concept for egg care overall, as they are much closer in relation to dinosaurs then any of the Crocodylomorphs are.

That's an exciting and trendy debate in itself: how birdlike in behaviour were the dinosaurs? which dinosaurs? did sauropods behave more like birds ...or elephants?

But I'm saying: more birdlike means better offspring survival. The crocodile is a living example of poor parenting. Are you trying to argue against my hypothesis or not?



For the record (seagypsy) I'll submit that I don't know enough, or what I do know is broken, or both. I have ideas, I have an internet connection, I try to be intellectually honest.

First off its Cretaceous, which is the second period of the Mesozoic era. And NO it does NOT support your argument in any way, and asserting it does is fallacious, and like a already stated they were shew sized, eg around 50-100 grams in weight and up to about 15cm long. This is a great size for being an insectavore (which the literature agrees with) and NOT a good size at all for any sort of egg predation.

Originally Posted by adelady

The crocodile is a living example of poor parenting.

Are you kidding? They've survived for 10s of millions of years. Maybe when our remote descendants have managed to do the same they might be able to make such observations. But we're in no position to do so. We haven't yet proven ourselves that successful.

Right, the crocodilians would say primates are a living example of poor ambush predators. And we truly do suck at that, compared to crocs. Must an order be good at all things to be successful? It doesn't work that way, everything has its strengths and weaknesses. Don't you find that mammals, birds, and probably dinosaurs, are better parents?

Originally Posted by Paleoichneum

First off its Cretaceous, which is the second period of the Mesozoic era.

Thanks, I'll try to remember. Memorization's a personal thing. I think "tri, jur, cret" to remember cretaceous is the third and last period.

Originally Posted by Paleoichneum

NO it does NOT support your argument in any way, and asserting it does is fallacious

Wait, so I'm saying "bird traits are good against egg predation", you're saying "think of dinosaurs like birds", yet you believe this contradicts my hypothesis that the mesozoic is characterized by adaptations against egg predation? I don't see the contradiction, unless you believe bird traits are not good against egg predation? Please reply whether (I'll be precise) paravians, in your opinion, were better adapted against egg predation than mesozoic contemporaries, or earlier forms.

I get the feeling you want to argue about whether dinosaurs are birds, with misinformed Pong believing they're like crocodile godzillas. If you reread my posts you'll see I really don't deserve correction on that.

I sense also that you want to argue the fine points of specific mammals' ability to endanger hard-shelled eggs, as if this disproves my hypothesis that adaptations like hard shell occurring during the mesozoic were against egg predation. I believe you know full well there were mammals substantially larger than 15cm even in the triassic, so I don't appreciate the dishonesty. Exactly what was attacking soft eggs is not important, because the eggs prove something was, just as a tortoise's shell proves something wants to chew on the tortoise.

If you must agree with me, don't get all-caps mad about it.

Originally Posted by Pong

Right, the crocodilians would say primates are a living example of poor ambush predators. And we truly do suck at that, compared to crocs. Must an order be good at all things to be successful? It doesn't work that way, everything has its strengths and weaknesses. Don't you find that mammals, birds, and probably dinosaurs, are better parents?

You used the statement to support claiming a low survival rate. Pointing out they've successfully survived for millions of years is valid.

Originally Posted by Pong

I get the feeling you want to argue about whether dinosaurs are birds, with misinformed Pong believing they're like crocodile godzillas. If you reread my posts you'll see I really don't deserve correction on that.

Yes, you do deserve it. You said that Crocodiles and Monitors were a better match. Did you not say that?

You have done a lot of waffling. You've been going back and forth so much that I have no idea anymore, what your original claims were. You were originally claiming that pressure from predation contributed to the extinction event.
Now, after that, you're claiming that protection from predation resulted from the pressures and the whole "extinction' factor has slipped out the window.

A lack of clarity on your part plus lots of waffling back and forth does not equal dishonesty from others.

Originally Posted by Neverfly

You used the statement to support claiming a low survival rate. Pointing out they've successfully survived for millions of years is valid.

Who's "they"? I said "they" the nests are 80% destroyed by predators. Adelady said "they" the order crocodilia has survived for millions of years. We're talking about different things. I'm not disputing the statement, but it's a poor argument against the observation that aside from their many strengths crocodiles are lousy at guarding their eggs.

Originally Posted by Neverfly

Originally Posted by Pong

I get the feeling you want to argue about whether dinosaurs are birds, with misinformed Pong believing they're like crocodile godzillas. If you reread my posts you'll see I really don't deserve correction on that.

Yes, you do deserve it. You said that Crocodiles and Monitors were a better match. Did you not say that?

Better match for what? I believe they're the best living examples of mesozoic reptiles that were not adapting to reduce egg predation. I use them in contrast to dinosaurs that developed more birdlike traits, and of course mammals. I am not matching them to dinosaurs. I am not arguing that dinosaurs are crocodiles. I brought them up to illustrate differences.

The only likening I've done is "in absence of evidence we should assume dinosaurs besides the paravians were no better parents (in terms of nurturing) than contemporary reptiles". I'm gonna drop that there and decline the bizarre debate with Paleoichneum about whether brontosaurus was "like a bird" in its maternal behaviours.

Originally Posted by Neverfly

You have done a lot of waffling. You've been going back and forth so much that I have no idea anymore, what your original claims were. You were originally claiming that pressure from predation contributed to the extinction event.
Now, after that, you're claiming that protection from predation resulted from the pressures and the whole "extinction' factor has slipped out the window.

A lack of clarity on your part plus lots of waffling back and forth does not equal dishonesty from others.

The dishonesty was a particular instance of portraying mesozoic egg predation as <100g shrews bruising their noses against 5mm thick hardened eggshell. It's a contrived and misleading picture.

Okay I'll stop waffling and say what I mean for the first time: The mesozoic is characterized by adaptations against egg predation. Egg predation is a stress. That makes it more a driver of selection than a cause of extinction. Though when a cataclysm like K–Pg wipes out 75% of species, the stressed ones are unlikely to survive.

Adelady said "they" the order crocodilia has survived for millions of years. We're talking about different things. I'm not disputing the statement, but it's a poor argument against the observation that aside from their many strengths crocodiles are lousy at guarding their eggs.

And turtles leave their eggs to hatch alone, get to the sea all by themselves and few actually make it through their first day. Very, very few make it to adulthood. The solution? More eggs. More chances for survival and reproduction.

And turtles are hardly alone here. Some creatures, corals are a good example but they're not alone, just eject their reproductive material into the ocean or other waters and it's up to environmental circumstances to determine how many meet up with other reproductive material and finish up as infant/adult organisms. Others take very good care and have social arrangements which promote survival of each individual's offspring, look at emperor penguins or those tree creches of Australian parrots.

No one species is any "better" a parent than another. They do what works for that species in that environment so far. And they're here to show that the strategy works. Who's to argue with that?

I'm not disputing those statements.

Honestly I think you just ripped a quote out where I remarked at the crocodile's poor maternal care of its eggs, responding as if I'd judged its survival to be poor. Now it looks like I'd judged its reproductive strategy to be poor and you're responding by making silly putty of the word "parent": an emperor penguin is a good parent, a coral is a good parent, a crocodile is a good parent.

In case you missed it, when I said "The crocodile is a living example of poor parenting" that was in response to Paleoichneum's "birds are the better concept for egg care overall". We were talking about care.

I don't know if it makes any difference in the debate but apparently the red belly turtle in Florida thinks pretty highly of alligator moms because they lay their eggs in alligator nests.

Florida Redbelly Turtle - Florida eco travel guide

Originally Posted by Pong

Better match for what? I believe they're the best living examples of mesozoic reptiles that were not adapting to reduce egg predation. I use them in contrast to dinosaurs that developed more birdlike traits, and of course mammals. I am not matching them to dinosaurs. I am not arguing that dinosaurs are crocodiles. I brought them up to illustrate differences.

I'm trying to follow you here:
Are you talking about why crocodiles/sluggish squat cold blooded reptiles survived the K/T event while others didn't?

Originally Posted by Pong

The dishonesty was a particular instance of portraying mesozoic egg predation as <100g shrews bruising their noses against 5mm thick hardened eggshell. It's a contrived and misleading picture.

How so?

Originally Posted by Pong

Okay I'll stop waffling and say what I mean for the first time: The mesozoic is characterized by adaptations against egg predation. Egg predation is a stress. That makes it more a driver of selection than a cause of extinction. Though when a cataclysm like K–Pg wipes out 75% of species, the stressed ones are unlikely to survive.

Ok good enough- now where's the evidence? I'm not saying I disagree; I am saying present the evidence.
Adaptations that led to hard shelled eggs rather than soft, like the snakes of the yellow ball python are today, for example may be due to predation but that is not the only possibility.

No time to read entire thread, but I like the "Egg crisis" theory.

But, hasnt there been quite a few extinction, since Im seeing that this dino lived in that era, that other dino live in that other area, etc, etc, its not like all types merrily lived until they all got extinct all at the same time?

But back to eggs, reptiles often dig to hide their eggs, do we have indications that dinos just laid the eggs there, which would explain the survival of crocodiles and turtles?



And, now Im reading that there was more Carbon dioxide back then, is this true? I had also read that there was a lot more oxygen? So was the atmospheric pressure higher or what? And if so, why is it going down, is there a leak?

Originally Posted by icewendigo

And, now Im reading that there was more Carbon dioxide back then, is this true? I had also read that there was a lot more oxygen? So was the atmospheric pressure higher or what? And if so, why is it going down, is there a leak?

yes more oxygen and more co2
as/re atmospheric pressure--I started a thread on that
atmospheric density over time?
It does seem that atmospheric pressure was higher then.

also water vapor (h2o) was much higher 100 million years ago.
and 100mybp seems to be when the planet started cooling

Originally Posted by Pong

Originally Posted by adelady

The crocodile is a living example of poor parenting.

Are you kidding? They've survived for 10s of millions of years. Maybe when our remote descendants have managed to do the same they might be able to make such observations. But we're in no position to do so. We haven't yet proven ourselves that successful.

Right, the crocodilians would say primates are a living example of poor ambush predators. And we truly do suck at that, compared to crocs. Must an order be good at all things to be successful? It doesn't work that way, everything has its strengths and weaknesses. Don't you find that mammals, birds, and probably dinosaurs, are better parents?

Originally Posted by Paleoichneum

First off its Cretaceous, which is the second period of the Mesozoic era.

Thanks, I'll try to remember. Memorization's a personal thing. I think "tri, jur, cret" to remember cretaceous is the third and last period.

Originally Posted by Paleoichneum

NO it does NOT support your argument in any way, and asserting it does is fallacious

Wait, so I'm saying "bird traits are good against egg predation", you're saying "think of dinosaurs like birds", yet you believe this contradicts my hypothesis that the mesozoic is characterized by adaptations against egg predation? I don't see the contradiction, unless you believe bird traits are not good against egg predation? Please reply whether (I'll be precise) paravians, in your opinion, were better adapted against egg predation than mesozoic contemporaries, or earlier forms.

I get the feeling you want to argue about whether dinosaurs are birds, with misinformed Pong believing they're like crocodile godzillas. If you reread my posts you'll see I really don't deserve correction on that.

I sense also that you want to argue the fine points of specific mammals' ability to endanger hard-shelled eggs, as if this disproves my hypothesis that adaptations like hard shell occurring during the mesozoic were against egg predation. I believe you know full well there were mammals substantially larger than 15cm even in the triassic, so I don't appreciate the dishonesty. Exactly what was attacking soft eggs is not important, because the eggs prove something was, just as a tortoise's shell proves something wants to chew on the tortoise.

If you must agree with me, don't get all-caps mad about it.

No there were no mammals larger then about shew size in the Triassic, And very very few non-mammal synapsids survived the Permian extinction, belonging to the groups Therocephalia and Cynognathids. They were pushed out by the middle of the Triassic and Dinosauria had taken dominance.

This I ahve shown no dishonesty, and you have shown more lack of knowledge while making a false accusation of me.

was just watching the history channel, and they tried to attribute the extinction to a pathogen. they kept saying that the youngest dinosaur fossils were from long before the asteroid (or maybe comet? i think i've seen recent research pointing to it being a comet) impact ever happened, and so the dinos had to have become extinct from something else. is it true that there are no fossils from around the time of impact?

Originally Posted by mat5592

is it true that there are no fossils from around the time of impact?

Not even close.
http://en.wikipedia.org/wiki/Alamosaurus
for example- they even found nests with eggs and embryos in them from that time.
History channel is as reliable as my grandmother.

not true(as per my education)
but
the dieoff of flora and fauna had already started,
with the stressors of atmospheric change, and the loss of parts of the food chain, the survivors would have had lower resistance to pathogens
.....................
as/re:

History channel is as reliable as my grandmother.

Were you intending to insult your grandmother?

Originally Posted by Neverfly

Originally Posted by mat5592

is it true that there are no fossils from around the time of impact?

Not even close.
History channel is as reliable as my grandmother.

don't worry, i'm fully aware of that (no offense to your grandmother). i had never heard it before so i figured i would ask. guess i could have done my own research, but i'm feeling extra lazy today.

I think Pong's got something in his hypothesis. Excessive vulnerability to predators is a very good reason for a species to shrink in size. The biggest prey are the most strongly hunted.

Since the rise of humanity as Mammoth hunters, almost all of the megafauna world wide died out. There used to be really big deer too, not just Mammoths. But the humans killed them too effectively. So now all that's left are a smaller populations of hairless elephant (living in places where other food sources are available for the humans), and the deer you see roaming today.


The Asteroid event hypothesis can explain what initially happened to kill off the dinosaurs of that era, but it does not explain why they didn't re-evolve back to larger sizes after the catastrophe had ended. If environmental conditions had motivated it to happen once, they should have motivated it to happen again.

Or one possibility I just thought of is that, I guess if mammals had moved into and filled all the "big reptile/bird" niches before the dinosaurs could re-evolve to be big again, then I guess they wouldn't evolve to fill a niche that's already full.

Originally Posted by kojax

Or one possibility I just thought of is that, I guess if mammals had moved into and filled all the "big reptile/bird" niches before the dinosaurs could re-evolve to be big again, then I guess they wouldn't evolve to fill a niche that's already full.

That post just reminded me of this video—

Originally Posted by seagypsy

I don't know if it makes any difference in the debate but apparently the red belly turtle in Florida thinks pretty highly of alligator moms because they lay their eggs in alligator nests.
Florida Redbelly Turtle - Florida eco travel guide

Brood parasitism is well illustrated by cuckoos. Although live-birth is an obvious protection against it, I don't know that calcified eggs in this case are an improvement - presumably softer more fragrant eggs would be easier to distinguish by mothers as their own? That modern birds who otherwise display keen parenting can be slavish victims of brood parasites, nurturing them and even watching stupefied as the parasites destroy competing young, suggests mesozoic reptiles including dinosaurs were susceptible. Arboreal nesting and flight are double edged swords here because canopy dinosaurs either sequester their nests from surface-laying freeloaders, or are better positioned to cuckoo the surface nesters.

Originally Posted by Neverfly

Originally Posted by Pong

Better match for what? I believe they're the best living examples of mesozoic reptiles that were not adapting to reduce egg predation. I use them in contrast to dinosaurs that developed more birdlike traits, and of course mammals. I am not matching them to dinosaurs. I am not arguing that dinosaurs are crocodiles. I brought them up to illustrate differences.

I'm trying to follow you here:
Are you talking about why crocodiles/sluggish squat cold blooded reptiles survived the K/T event while others didn't?

Thanks, you're zeroing in. I'm talking about how one particular stress (egg predation) throughout the mesozoic promoted adaptations resistant to egg predation, as seen in the evolution toward birds. A consequence of this is that species still under egg predation stress during a cataclysm are more likely to die out.

Originally Posted by Neverfly

Originally Posted by Pong

The dishonesty was a particular instance of portraying mesozoic egg predation as <100g shrews bruising their noses against 5mm thick hardened eggshell. It's a contrived and misleading picture.

How so?

I'll admit to being out of my depth regarding the exact characteristics of all eggs during that era, or the full range of potentially egg-eating mammals. But to say that mesozoic mammals were <100g shrews is disingenuous; most were this small yes. The source I had saying that a meter-long mammal dates as early as the triassic I think is wrong; such brutes shouldn't exist until the late era... but I don't see the point to this discussion in placing exactly which periods included which sizes. And to say eggshell was hardened 5mm thick is cherrypicking; few eggs of the mesozoic had this property. Above all the picture is a strawman because egg predation does not just mean mammals attacking massive hardened dinosaur eggs. Even if not one mammal ever compromised a single egg of any kind throughout the entire mesozoic, this side issue would not disprove my hypothesis. Recall that not too long ago we were all surprised to find oviraptor wasn't caught in the act of egg-eating; so the idea that even dinosaur eggs got predated is not a fringe belief I should have to argue here.

Originally Posted by Neverfly

Originally Posted by Pong

Okay I'll stop waffling and say what I mean for the first time: The mesozoic is characterized by adaptations against egg predation. Egg predation is a stress. That makes it more a driver of selection than a cause of extinction. Though when a cataclysm like K–Pg wipes out 75% of species, the stressed ones are unlikely to survive.

Ok good enough- now where's the evidence? I'm not saying I disagree; I am saying present the evidence.
Adaptations that led to hard shelled eggs rather than soft, like the snakes of the yellow ball python are today, for example may be due to predation but that is not the only possibility.

Well, through most of this debate my would-be opponents have been dishing up the evidence because they got my meaning backwards. Like arguing harder eggs are resistant to gnawing by vermin, or dinosaurs with the activity level of coyotes could easily dispatch vermin and nest robbers. Perhaps I should'a strung you along for more.

I'm wary of "may be due to ... but that is not the only possibility" type discussions, because too often people on this forum push single explanations for an adaptation. IMO practically all traits carry multiple or nebulous advantages and disadvantages.

I can't supply physical evidence, but the indirect evidence seems compelling. For examples I've no evidence any flier of the mesozoic ever nested on a tree, cliff, or barren island; or that baby mammals ever shrieked out an alarm when threatened, while neighbouring dinosaur eggs were devoured in stealth; but we easily accept the value of such adaptations observed in modern species as self-evident.

Originally Posted by kojax

I guess if mammals had moved into and filled all the "big reptile/bird" niches before the dinosaurs could re-evolve to be big again, then I guess they wouldn't evolve to fill a niche that's already full.

That's pretty much consensus, but eggs have a fundamental disadvantage at the larger size range. The reason is that, while a giraffe may birth a calf nearly two meters tall, so it begins life competing on a comparable level, egg size is constrained by shell thickness, which is constrained by the embryo's need to respirate through the egg... so hatchlings of huge dinosaurs are relatively undersized and face very different predators and prey than their parents. That could be turned to advantage, as we see with animals that employ metamorphosis. But it tends to suppress specialization in large reptiles because their bodies must function well in multiple niches.

And, now Im reading that there was more Carbon dioxide back then, is this true?

Yup. In earlier times it was even higher. All nicely offset by the fact that the sun was cooler.

Originally Posted by Pong

I'll admit to being out of my depth regarding the exact characteristics of all eggs during that era, or the full range of potentially egg-eating mammals. But to say that mesozoic mammals were <100g shrews is disingenuous; most were this small yes. The source I had saying that a meter-long mammal dates as early as the triassic I think is wrong; such brutes shouldn't exist until the late era...

What exactly does your source claim? What is your source?

Originally Posted by Pong

but I don't see the point to this discussion in placing exactly which periods included which sizes.

When the time period you are discussion between dates is at least 56 million years and upwards of 180 million years! YES it is very important to make distinction regarding what periods/eras/stages are being referenced. you are trying to make hypothesis based on a period of time longer then when the dinosaurs died of and now.

Originally Posted by Pong

And to say eggshell was hardened 5mm thick is cherrypicking; few eggs of the mesozoic had this property.

I pointed out this particular information to show that hard shells had already evolved much earlier then your initial hypothesis and comments were talking.

And what is your source saying that few were comparable?

Originally Posted by Pong

Above all the picture is a strawman because egg predation does not just mean mammals attacking massive hardened dinosaur eggs. Even if not one mammal ever compromised a single egg of any kind throughout the entire mesozoic, this side issue would not disprove my hypothesis. Recall that not too long ago we were all surprised to find oviraptor wasn't caught in the act of egg-eating; so the idea that even dinosaur eggs got predated is not a fringe belief I should have to argue here.

It is a fringe hypothesis, because you are placing a much larger emphasis on the impact of egg predation on the extinction then there is any evidence for.

Originally Posted by Pong

Thanks, you're zeroing in. I'm talking about how one particular stress (egg predation) throughout the mesozoic promoted adaptations resistant to egg predation, as seen in the evolution toward birds. A consequence of this is that species still under egg predation stress during a cataclysm are more likely to die out.

This is why I point out the nature of speculation. Speculating in itself is not bad... but when trying to build a picture, you need to keep your speculations separate from your conclusions.
So, you decide to examine an ecosystem from 180 million years ago.
You start with what you know and what fossil evidence there is. You speculate to fill in the gaps, given the data about the end result.
If you clump your speculations with your conclusions, you won't know what you're doing, won't keep track and will confuse yourself. You won't easily find which speculation was in error and be able to backtrack to correct it.
It's a bit of detective work piecing the puzzle together and should be done carefully.

Originally Posted by Pong

But to say that mesozoic mammals were <100g shrews is disingenuous; most were this small yes. The source I had saying that a meter-long mammal dates as early as the triassic I think is wrong; such brutes shouldn't exist until the late era...

What makes you think it's wrong- what is the source? Why do you declare that they shouldn't exist?
Do you realize mammal-like predators larger than a Volkswagon were roaming the earth as early as 300 million years ago?

Originally Posted by Pong

but I don't see the point to this discussion in placing exactly which periods included which sizes.

This is what Seagypsy pointed out earlier. You're clumping together almost 370 million years of total time into one era.
It's absofrickenlutly relevant what time frame we're talking about.

Originally Posted by Pong

And to say eggshell was hardened 5mm thick is cherrypicking; few eggs of the mesozoic had this property.

Evidence?

Originally Posted by Pong

Above all the picture is a strawman because egg predation does not just mean mammals attacking massive hardened dinosaur eggs. Even if not one mammal ever compromised a single egg of any kind throughout the entire mesozoic, this side issue would not disprove my hypothesis.

Uhhh... if it never happened, then yet, it shows an error in your hypothesis.

Originally Posted by Pong

Well, through most of this debate my would-be opponents have been dishing up the evidence because they got my meaning backwards. Like arguing harder eggs are resistant to gnawing by vermin, or dinosaurs with the activity level of coyotes could easily dispatch vermin and nest robbers. Perhaps I should'a strung you along for more.

Bull. When you present a hypothesis, be prepared to see that it withstands attack and scrutiny.

Originally Posted by Pong

I'm wary of "may be due to ... but that is not the only possibility" type discussions, because too often people on this forum push single explanations for an adaptation. IMO practically all traits carry multiple or nebulous advantages and disadvantages.

Agreed. Ecosystems are complex and very diverse. Focusing on single cause is often a mistake- but not always. A single cause can have dramatic repercussions, such as the K/T event itself.

Originally Posted by Pong

I can't supply physical evidence, but the indirect evidence seems compelling. For examples I've no evidence any flier of the mesozoic ever nested on a tree, cliff, or barren island; or that baby mammals ever shrieked out an alarm when threatened, while neighbouring dinosaur eggs were devoured in stealth; but we easily accept the value of such adaptations observed in modern species as self-evident.

What?

Originally Posted by adelady

And, now Im reading that there was more Carbon dioxide back then, is this true?

Yup. In earlier times it was even higher. All nicely offset by the fact that the sun was cooler.

I'm thinking if there was less oxygen, that might effect selection toward larger sizes more directly also. Bigger creatures have slower metabolisms. They still need more food per day, but proportionally they're metabolizing it slower. I'm thinking a bigger creature can take longer, slower breaths to fill its lungs full of lots of oxygen and absorb it slowly. Also, because if it's warm blooded, then the huge size means it's easier to maintain its core temperature.

Smaller creatures with fast metabolisms maybe couldn't get enough oxygen to keep going? That would also explain why some of the most notable fliers of that era, like pterodactyls, were gliders instead of active fliers. Perhaps they were not able to get enough oxygen into the system fast enough to actually flap those wings at a high rate? (Or actually it seems wiki has them as possible active fliers with auxiliary respiration devices in their wings.)

Pterosaur - Wikipedia, the free encyclopedia

Originally Posted by wiki

As evidenced by hollow cavities in the wing bones of larger species and soft tissue preserved in at least one specimen, some pterosaurs extended their system of respiratory air sacs (see Paleobiology section below) into the wing membrane itself.

So... maybe one reason huge creatures were workable is because they didn't have as stiff a competition from faster, smaller, more agile opponents? In the modern world, pack hunters of smaller size quite often win against bigger prey. A pack of dogs is the most effective and easy way to take down a bear. A pack of humans is the most fierce threat to a mammoth.

Another quick hop in and out,

another way of asking the question, to step back with another perspective, would be to flip the question around and ask:

"Why have the ancestors of Birds and Reptiles survived?"

small size (needing little food) low metabolism (ditto) and/or fast generation times (fast bounce-back after population crash)

Circa 68mybp the southern rockies rose up out of a shallow sea with amazing speed. About the same time, the deccan traps were formed. (I've yet to find conclusive data as/re the interrelation of these events)
Add in the drop in atmospheric oxygen from 35ppm to 29ppm by the time(65.5mybp) of the impact and the great die-off.
It seems that the world/climate of the dinasaurs was undergoing rapid change. It also seems that very large animals are more niche bound than smaller ones.
The dinosaurs were dying off (fewer extant species) before the impact.

The problem is figuring out why mammals took over the "big land animal" niche. Both small dinosaurs and small mammals survived the extinction. Why didn't the dinosaurs take back the "big land animal" niche again after it was over? How is it that, the first time around the dinosaurs got that niche, but the second time around the mammals got it?

Clearly the existing large mammals are descended from smaller mammals. How did mammals win that evolution race?

Originally Posted by kojax

The problem is figuring out why mammals took over the "big land animal" niche. Both small dinosaurs and small mammals survived the extinction. Why didn't the dinosaurs take back the "big land animal" niche again after it was over? How is it that, the first time around the dinosaurs got that niche, but the second time around the mammals got it?

Maybe it was all that added mass from the asteroid that got absorbed by the planet. Earth is just too big to let big animals get around so well.

lol jk

I think it has something to do with the amount of O₂ in the atmosphere. There isn't enough to allow things to get freakishly huge anymore. Including insects.

Originally Posted by kojax

The problem is figuring out why mammals took over the "big land animal" niche. Both small dinosaurs and small mammals survived the extinction. Why didn't the dinosaurs take back the "big land animal" niche again after it was over? How is it that, the first time around the dinosaurs got that niche, but the second time around the mammals got it?

Clearly the existing large mammals are descended from smaller mammals. How did mammals win that evolution race?

As for why Dinosaurs got it the first time, its due to mammals not existing yet, remember that when asking things.

Remembering that Birds were the small dinos that survived, you only have to look at the Paleocene/Eocene/Oligocene to see that in a number of places large ground dwelling birds DID take over for a while.

Originally Posted by seagypsy

Originally Posted by kojax

The problem is figuring out why mammals took over the "big land animal" niche. Both small dinosaurs and small mammals survived the extinction. Why didn't the dinosaurs take back the "big land animal" niche again after it was over? How is it that, the first time around the dinosaurs got that niche, but the second time around the mammals got it?

Maybe it was all that added mass from the asteroid that got absorbed by the planet. Earth is just too big to let big animals get around so well.

lol jk

I think it has something to do with the amount of O₂ in the atmosphere. There isn't enough to allow things to get freakishly huge anymore. Including insects.

actually huge insects went away at least 200 million years before that at the end of the Carboniferous

Originally Posted by Paleoichneum

Originally Posted by seagypsy

Originally Posted by kojax

The problem is figuring out why mammals took over the "big land animal" niche. Both small dinosaurs and small mammals survived the extinction. Why didn't the dinosaurs take back the "big land animal" niche again after it was over? How is it that, the first time around the dinosaurs got that niche, but the second time around the mammals got it?

Maybe it was all that added mass from the asteroid that got absorbed by the planet. Earth is just too big to let big animals get around so well.

lol jk

I think it has something to do with the amount of O₂ in the atmosphere. There isn't enough to allow things to get freakishly huge anymore. Including insects.

actually huge insects went away at least 200 million years before that at the end of the Carboniferous

Well that's what I get for thinking. Thanks for the correction.... sneaks off to look up "carboniferous"....

Originally Posted by Paleoichneum

As for why Dinosaurs got it the first time, its due to mammals not existing yet, remember that when asking things.

but well-advanced therapsids close to the mammalian grade DID exist, they just got smaller towards the end, while dinosaur quickly became far bigger than its precursors such as Lagosuchus
remember also that, although dinosaurs had become a noticeable part of the ecosystems in the late Triassic, it was only after the extinction of its rival archosaurs such as Phytosaurs, Ornithosuchians, Rauisuchians etc near the end of the Triassic that dinosaurs became fully dominant as the only sizeable tetrapods on land

Originally Posted by marnixR

Originally Posted by Paleoichneum

As for why Dinosaurs got it the first time, its due to mammals not existing yet, remember that when asking things.

but well-advanced therapsids close to the mammalian grade DID exist, they just got smaller towards the end, while dinosaur quickly became far bigger than its precursors such as Lagosuchus
remember also that, although dinosaurs had become a noticeable part of the ecosystems in the late Triassic, it was only after the extinction of its rival archosaurs such as Phytosaurs, Ornithosuchians, Rauisuchians etc near the end of the Triassic that dinosaurs became fully dominant as the only sizeable tetrapods on land

Very true, thanks marnixR

GOD ALMIGHTY killed the dinosaurs.

Originally Posted by parag29081973

GOD ALMIGHTY killed the dinosaurs.

Show the evidence

Originally Posted by Paleoichneum

Originally Posted by parag29081973

GOD ALMIGHTY killed the dinosaurs.

Show the evidence

Isn't the thread asking why? Doesn't matter how God might have done it or what kind of evidence was left behind, so maybe parag can tell us the reason. Probably had something to do with God wanting to introduce moronic thought and bring idiots into the world.

I mean look at the job done by GOD. So complete. So effecient. So beautiful. Only GOD can kill with such power and effeciency.

Originally Posted by parag29081973

I mean look at the job done by GOD. So complete. So effecient. So beautiful. Only GOD can kill with such power and effeciency.

Why does your god enjoy killing things so much? She seems to do an awful lot of it.

And it wasn't that efficient. They are still around ...

Originally Posted by Strange

She seems to do an awful lot of it.

So... that whole Noahs ark thing...


Did God have an abortion?

Originally Posted by Strange

Originally Posted by parag29081973

I mean look at the job done by GOD. So complete. So effecient. So beautiful. Only GOD can kill with such power and effeciency.

Why does your god enjoy killing things so much? She seems to do an awful lot of it.

And it wasn't that efficient. They are still around ...

True, some of them with their tiny little brains outsmarted god.

Originally Posted by Neverfly

Originally Posted by Strange

She seems to do an awful lot of it.

So... that whole Noahs ark thing...

That is how we know she is female: so bloody inconsistent!

I don't think God is the one you're going to have to worry about after saying that...

Originally Posted by Strange

Originally Posted by Neverfly

Originally Posted by Strange

She seems to do an awful lot of it.

So... that whole Noahs ark thing...

That is how we know she is female: so bloody inconsistent!

And perfectly vicious in her wrath. Although, I think I could have done it way way better. For instance, death is an unnecessary mercy.

Originally Posted by seagypsy

Originally Posted by Strange

That is how we know she is female: so bloody inconsistent!

And perfectly vicious in her wrath. Although, I think I could have done it way way better. For instance, death is an unnecessary mercy.

Maybe I should go into hiding now....

Originally Posted by Strange

Originally Posted by seagypsy

Originally Posted by Strange

That is how we know she is female: so bloody inconsistent!

And perfectly vicious in her wrath. Although, I think I could have done it way way better. For instance, death is an unnecessary mercy.

Maybe I should go into hiding now....

Don't worry, Strange, if I were god, I'd resign immediately after making myself human. Existence is boring without any risks.
http://www.youtube.com/watch?v=B4CRkpBGQzU

Originally Posted by parag29081973

I mean look at the job done by GOD. So complete. So effecient. So beautiful. Only GOD can kill with such power and effeciency.

It was neither complete nor efficient. So show me the specific evidence that shows any supernatural influnace

Originally Posted by parag29081973

I mean look at the job done by GOD. So complete. So effecient. So beautiful. Only GOD can kill with such power and effeciency.

I think you're pulling legs, here.

Poe's Law?

I agree with PumaMan and the Alvarez Theory.

Originally Posted by Paleoichneum

It is a matter of degrees, and the growth structuring seen in bone sectioning taken from many different genera all display the same patterning as seen in birds. this they had a comparable "warm-bloodedness"

Perhaps but I'm not convinced. Dinosaurs were warm-blooded? How could scientists have been so sorely mistaken for all these years? Do you have some peer-reviewed papers to share?

Ahhh...nevermind. I found an article:

Dinosaurs were warm-blooded reptiles: Mammal bone study sheds light on dinosaur physiology

The study analysing the lines of arrested growth (LAG) in the bones of around a hundred ruminants, representative of the specific and ecological diversity of that group of mammals. The results show that the presence of these lines is not an indicator of an ectothermic physiology (does not generate internal heat), as had previously been thought, since all warm-blooded mammals have them. The study therefore dismantles the key argument of the hypothesis that dinosaurs could have been cold-blooded reptiles.
The work was carried out by Meike Köhler, ICREA researcher and ICP palaeontologist; Ronny Aanes, researcher from the Norwegian Polar Institute; Nekane Marín, PhD student at the UAB and Xavier Jordana, lecturer of postgraduate studies at same university.
LAGs are seen in bone sections as dark rings, similar to those seen in tree trunks. The rings are formed, both in the studied mammals and in trees, during the unfavourable seasons (winter or dry season) when the growth of the organism is arrested as a result of a lack of resources. The presence of LAGs in bones was, until now, considered to be the clearest indicator of ectothermy since the seasonal arrest of growth was related to the animal's inability to maintain a more or less constant body temperature (endothermy) during the season of scarce resources.
Meike Köhler explains: "the study we have carried out is very powerful, both in terms of the amount of material and the diversity of species with which we worked, but we did not design it to find a response to the thermophysiology of dinosaurs. We sought to better understand the physiology of extant mammals and how the environment affects them -- how their growth changes as a result of external temperatures, rain and the availability of food and water."
Understanding this was the first step to establishing discussions in paleontological research about the physiology of animals that lived several million years ago.
But the researchers realised that what they observed in the bones of different ruminants refutes the main argument for an ectothermic physiology in dinosaurs. Many hypotheses set out from the premise that large mammals -- endothermic par excellence -- do not have LAGs in their hard tissues since they do not need to arrest their growth responding to external temperature conditions. In fact, since LAGs have been observed in almost all species of dinosaur, many scientists considered that they were cold-blooded reptiles.
The article published in Nature offers the first systematic study, based on an extensive sample of mammals representative of a large variety of ecosystems, which shows that LAGs do not indicate an ectothermic physiology but give us information about how the physiology (metabolism) of an animal changes according to seasonal endocrinal changes, both in cold- and warm-blooded animals. These changes represent a common heritage in all vertebrates and are a kind of internal clock that regulates the animals' needs according to the seasonal availability of resources. Despite the fact that these physiological changes have a strong genetic component, they are also functional and their intensity depends on the ecological conditions in which the animals live. The main ecological factors are more rain and limited supply of food and water, rather than external temperature. This discovery opens up a major line of research into the conservation of biodiversity on our planet today.

If this is true, then why did only mammals survive the mass extinction and not small dinosaurs? I thought that mammals survived largely because they were endothermic and didn't need to rely on external temperatures as much (and they could burrow and hibernate, etc). Or did small mammals simply outcompete the small dinosaurs which survived...or did they go extinct earlier on and weren't even there to compete with in the first place?

Originally Posted by parag29081973

I mean look at the job done by GOD. So complete. So effecient. So beautiful. Only GOD can kill with such power and effeciency.

I think God missed one in Pat Robertson.

Originally Posted by mikepotter84

If this is true, then why did only mammals survive the mass extinction and not small dinosaurs? I thought that mammals survived largely because they were endothermic...

Yes, how are mammals fundamentally different..?


I dunno why offspring predation isn't taken more seriously. Do we suppose the live birth adaptation was just for fun?

Yes, how are mammals fundamentally different..?

Tribosphenic cheek teeth and a diversified diet at the time may have made them different enough to survive, perhaps (?)

What's wrong with the simplest answer?

I never said there was anything wrong with your answer.

Originally Posted by mikepotter84

If this is true, then why did only mammals survive the mass extinction and not small dinosaurs?

Birds are (descendants of [small?]) dinosaurs.