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dinosaur extinction

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Guest willem

does the idea of a huge meteor extinting 75% of all life forms satisfy you? yes or no.

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How about the other theory that they ate so much that there was nothing left for them to eat so they ate each other and the last one standing died of starvation?

 

A meateor sounds like a good theory to me and I have heard some of the facts that back it up but I don't think they have proved it yet.

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There's a giant crater in the yucatan I believe that coincides with the extinction of the dinosaurs, and was probably the source of the iridium that defines the KT Boundary. And such a drastic extinction was probably caused by a drastic event. As someone in some book somewhere once said, the most important changes happen in the blink of an eye. But it's unlikely they'll ever be able to prove it.

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How about the other theory that they ate so much that there was nothing left for them to eat so they ate each other and the last one standing died of starvation?

 

That automatically rasies the question of "Why?" Why would a group of animals that has been spectacularly sucessful for so long sudden begin to "over-eat"?

 

From what I've been able to gather, there was a lot of stuff happening at the time, especially climate change. Nothing alone would have killed them, but the meteor hit at *just* the wrong time, delivering a knockout blow, so to speak.

 

Mokele

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Dont get me wrong -- dinosaurs are hard-core... but i dont think that they could survive the earth being hit by an effing huge metiore, even if theire taxa were in the prime of health and the climate were all hunky-doory for them.

 

Although, having said that, arent crocodyles dinosaurs? which would make the dinosaurs not actually extinct.

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Crocs and such are related to them, but aren't dinos. They either are archosaurs, or are closely to them (I forget), from which dinosaurs evolved. But, birds are evolved directly from dinosaurs, and I think might still qualify as such (toothless, beaked dinosaurs, most modified for flight).

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One of the main differences between today's lizards and dinosaurs is how the legs are joined to the hip. Dinosaurs walked with their legs perpendicular to the ground. Crocodiles and most lizards walk with their legs almost parallel to the ground. It has to do with how the hip socket is formed.

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One of the main differences between today's lizards and dinosaurs is how the legs are joined to the hip. Dinosaurs walked with their legs perpendicular to the ground. Crocodiles and most lizards walk with their legs almost parallel to the ground. It has to do with how the hip socket is formed.

 

Do you know why this is? why the hip sockets have changed in the manner they have?

 

Regards

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Crocs and such are related to them, but aren't dinos. They either are archosaurs, or are closely to them (I forget), from which dinosaurs evolved.

 

Both crocs and dinos are archosaurs (as are birds, technically), but crocs are not dinos, while birds are.

 

Crocodiles and most lizards walk with their legs almost parallel to the ground. It has to do with how the hip socket is formed.

 

More or less. While, AFAIK, no lizard has ever achieved a fully errect gait, the first crocodylians actually resembled reptilian greyhounds (small, fast, erect-running). While the main line of crocodylian evolution has been the form we all see today, there have been numerous returns to fully-upright posture among prehistoric crocs.

 

And the hip socket is more of a consequence than a cause. Basically, lizards don't have a diaphragm, and use contractions of the rib muscles to breathe (along with buccal pumping, involving the floor of the mouth). But they also use those muscles for locomotion, setting up a conflict of interest: any locomotion requiring lateral flexion of the body (which is basically everything above a slow crawl for sprawling animals) makes breathing impossible. This is why lizards run a short distance, stop, run, stop, etc. If they run continuously, they exhaust themselves.

 

Erect posture solves this problem: it allows the animal to run and breathe at the same time. This, in turn, makes higher aerobic scope (range of sustainible speeds) a possibility, which comes from higher metabolism, which leads to endothermy.

 

This site goes into some details about the gaits of dinosaurs (and consequently, hip structure, mostly concerning bipedality)

 

Seems good, but the conclusion (hopping dinos) is dead wrong, and based on some flawed assumptions (limited lateral and torsional motion of the femur prevents fast running? Has that guy ever seen an ostrich?). It's also contradicted by fossil evidence: hopping is pretty damn crappy as far as locomotion *unless* there's an elastic ligament involved. This ligament is present in all hoppers today (and actually makes them even more efficient than runners) and leaves *very* obvious signs on a skeleton (namely the attachment point), which I have seen in precisely 0 theropod skeletons to date.

 

Mokele

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Seems good' date=' but the conclusion (hopping dinos) is dead wrong, and based on some flawed assumptions (limited lateral and torsional motion of the femur prevents fast running? Has that guy ever seen an ostrich?).

 

Mokele[/quote']

 

What's wrong with a hopping dino? I think there were some footprint fossils found in a riverbed, and from the stride they inferred the thing could 'hop'.

 

Not sure about it. But Coquina is right, the biggest difference between dinosaurs, and lizards of today, is how the hip socket is configured.

 

Look at the pattern:

 

1. snakes

2. turtles

3. crocodiles

4. alligators

5. others

 

They all seem, umm, like pushed to the ground.

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What's wrong with a hopping dino?

 

You mean aside from the total lack of an anatomical feature that is necessary to make hopping energeticly worthwhile?

 

I think there were some footprint fossils found in a riverbed, and from the stride they inferred the thing could 'hop'.

 

1) I'd like to see a source for that.

 

2) Did the trackway show actual hopping, or just convince people that maybe they could, at some point, hop? We have trackways that prove dinosaurs could run, when they remained below a certain size (just like how modern elephants can't run). Technically they probably could hop, of course, but not as a primary mode of locomotion for extended distances like kangaroos do.

 

Also, it should be noticed that the only "hopper" large than a rabbit is a kangaroo, and the only reason they hop is because that's the only mode of fast locomotion availible to them. They cannot evolve the specializations needed for fast, quadrupedal running because, as marsupials, they need dextrous forelimbs to move into the mother's pouch.

 

But Coquina is right, the biggest difference between dinosaurs, and lizards of today, is how the hip socket is configured.

 

It is *a* difference, but certainly not the biggest. Other differences, such as hepatic piston respiration, the 4-chambered heart, skull morphology, feathers, and possibly endothermy, would all be "bigger" differences.

 

Look at the pattern:

1. snakes

2. turtles

3. crocodiles

4. alligators

5. others

They all seem, umm, like pushed to the ground.

 

I could quibble the with the snakes on the ground bit by pointing you to the recent series of papers in the Journal of Experimental Biology on Chrysopelea genus, the gliding tree snakes, but I won't.

 

I will, however, note that not only does posture become more erect with size (in both mammals and reptiles), but that modern crocodilians technically are half-erect. Look at the back legs during a high-walk: they're straight up and down, like a mammal's, even though the front limbs are only semi-erect.

 

Modern crocodilians (alligators, caimans, crocs and gharials) evolved from the Sphenosuchians, a clade of archosaurs that looked, for all the world, like reptilian greyhounds. They were about the same size, similarly sleek, and had long, upright legs. The modern condition of crocodilians is a secondary reversion to the sprawling state, an adaptation for their unique lifestyle as shoreline hunters. Every time they've left that niche for land, erect walking has returned.

 

However, what reptilian and dinosaurian locomotion has to do with the KT extinction is beyond me.

 

Mokele

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Ok, I'll admit you make some good points, but you seem to have glossed over the possible actual fact, which is that there was at least one species of Dinosaur who "hopped."

 

Let me see if i can find you a site, with the footprint thing i mentioned.

 

And 'biggest' was probably not required, it happens to interest me very much though, this particular difference.

 

This is such an exciting topic for me, I've always loved dinosaurs, allosaurus, stegosaurus, etc etc

 

Let me see if i can find a link. This is a break from me thinking about physics/math all the time.

 

 

Well, not surprisingly i couldn't find the name of the riverbed, but i saw a documentary on it years ago, i think it was someplace in the center US.

 

Nonetheless, i think my main point has been missed, which is why do modern lizards appear "sqashed" to the ground, when the dinosaurs could 'hop' or certainly run on two legs, probably quite fast.

 

Imagine a hungry giant fanged creature coming at you. You would hop one mile if you could.

 

Regards

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Ok, I'll admit you make some good points, but you seem to have glossed over the possible actual fact, which is that there was at least one species of Dinosaur who "hopped."

 

1) I'm not convinced that such a fossil trackway exists. If you're referring to the trackway in which we observe an acrocanthosaur killing a large sauropod, the "hop" mentioned in the popular press is *not* what is kinematically classified as a "hop", but is merely a perfectly ordinary gait change.

 

2) I'm not arguing that dinosaurs could not hop, or never hopped, only that it was not their primary mode of rapid locomotion. We can hop too, but we don't when faced with a threat, because running is far more efficient and faster for us.

 

Nonetheless, i think my main point has been missed, which is why do modern lizards appear "sqashed" to the ground, when the dinosaurs could 'hop' or certainly run on two legs, probably quite fast.

 

Because it's the ancestral state. For them, it remains useful. While their stance limits endurance for reasons already mentioned above, it does not limit burst speed nor is it actually any less efficient. For small animals who do not need endurance-based escapes, this is fine, and may actually be preferable, as it allows them to fit into hiding spaces not availible to erect-walkers.

 

Erect walking only makes sense in a narrow set of conditions, which is for an organism which can profit from high endurance enough to justify the resultant required increase in basal metabolism. Your maximum endurance is always roughly 10x your basal metabolism. So if an animal gains the ability to run at faster sustainable speeds, it pays the cost of having to fuel that higher metabolism 24/7. For many animals, the cost just isn't worth it. Evidently, for primitive mammals and archosaurs, it was worth it.

 

Mokele

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Coquina brought up a very good point, about the hip bone, which connects to the very reason I got involved in this thread in the first place... because almost twenty years ago, I figured out what killed the dinosaurs.

 

I have sort of been dancing around the answer, to see what responses I'd get, but it seems this thread has died, so I will finally reveal my hidden motive for discussing the 'hip bone' issue, and the 'hopping' dinosaur issue.

 

The theory came to me as i was reading an encyclopedia article on dinosaurs. It was an old encyclopedia, and there was an artists rendition of a bunch of dinosaurs. The sketch was of a beach line, and showed some dinosaurs in the ocean. Off in the distance, there was a brontosaurus, with an extremely long neck. In the air, there was a pterydactl flying.

 

Now, I looked at this picture for a very long time, because something just didn't seem right, though I wasn't sure what.

 

Then it hit me all at once.

 

"How could something that big hold its neck up against the pull of gravity?How could something that heavy fly? Why were dinosaurs so big compared to the sizes of animals today?"

 

Now at that time, I'd already learned the Newtonian theory of gravity, and I reasoned as follows:

 

[math] F_{gravity} = G \frac{M_{earth} m_{dino}}{R^2} [/math]

 

Dinosaur weight = w = mg, therefore

 

[math] F_{gravity} = \frac{G}{g} \frac{M_{earth} w_{dino}}{R^2} [/math]

 

 

Postulate: In the prehistoric past, before the moment of dinosaur extinction, the force of gravity of earth was less.

 

Let w denote the weight of the dinosaur before earths gravity changed, and let W denote the weight of the same dinosaur moments after earth's gravity suddenly dramatically changed.

 

Right after something drastic happened, Pterydactyls were too heavy to fly, and were pinned to the earth.

 

The brontosaurus could no longer hold up his neck.

 

Alligators which used to be able to run, were now squashed.

 

Snakes which maybe used to have tiny legs, learned to slither on their bellies.

 

Turtles, now took to water to ease the burden of the increase in gravity on their ability to move.

 

Etc, you hopefully get the idea here.

 

So then i thought, how much would be enough to devestate them?

 

Doubling their weight seemed good, but possibly hard to achieve using the equation above.

 

The idea ended up being this...

 

Before the dinosaurs died, earth had a second moon, a prehistoric moon.

 

Hence the prehistoric moon theory of dinosaur extinction.

 

The moon spiralled in, blanketed the KT boundary with iridium, as it spiraled around faster and faster.

 

I figured that a 1.5 increase in their weight seemed appropriate, and do-able, within the framework of Newton's gravity formula.

 

Well so anyways, that's why i chimed in when I saw Coquina's comment about the hip bones. It made me think of my theory.

 

Also one more thing.

 

Before you go trying to down a theory, that can't possibly be downed, let me send you one additional thing to think about, which is this...

 

http://www.edwardtbabinski.us/mpm/struthers.html

 

And here is the relevent quote:

 

SEE THE TWO DIAGRAMS OF THE RIGHT WHALE'S PELVIS, FEMUR AND TIBIA

(based on dissections by Struthers)

 

"Nothing can be imagined more useless to the animal than rudiments of hind legs entirely buried beneath the skin of a whale, so that one is inclined to suspect that these structures must admit of some other interpretation. Yet, approaching the inquiry with the most skeptical determination, one cannot help being convinced, as the dissection goes on, that these rudiments [in the Right Whale] really are femur and tibia. The synovial capsule representing the knee-joint was too evident to be overlooked.

 

The inescapable conclusion is this...

 

Whales used to be able to walk on land.

 

Which brings me to the very first post of this thread:

 

does the idea of a huge meteor extinting 75% of all life forms satisfy you? yes or no.

 

Nope.

 

 

Regards

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#1 Sure there were running crocs, but there were also many varieties just like those that exist today. And even so, the ones around today can make mad dashes. There wer also some even more thoroughly evolved for a marine lifestyle. Under your conclusion, what would lead to their extinction?

 

#2 Turtles largely evolved for the water, prior to the KT event, whereas tortoises evolved for the land, where they remain today.

 

#3 Though younger than lizards by far, legless snakes did exist before the KT event.

 

#4 Now I'm not positive about this, but I believe that prior to the KT Event only a single known pterosaur remained in existance, Quetzalcoatlus, which, due to its specific niche, was not outcompeted for by birds. And yes, while it was certainly very large, its light bone structure weighed about as much as a man. Combining thermals and an impressive surface area for its tremendous wings, flight isn't so farfetched.

 

#5 Yes, whales were descended from small terrestrial mammals Long AFTER the KT Event, from semi-aquatic creatures such as Ambulocetus. Trace their evolution further and eventually you get to fully aquatic whales. Further along, and obviously, you encounter modern whales. And the similar bone structure of their limbs can be deduced to nothing more than the easiest frame-work under which their former legs could evolve into flippers. Why evolve a new skeletal paddle entirely when you can easily adjust the limbs you've got? Their remaining hindlimbs are simply vestigial, like the leftover eyes in blind cavefish.

 

#6 My biggest problem with your moon theory is the fact that a moon spiralling around like that would majorly disrupt all those little balances maintained by the moon today, such as wobble, tides, and magnetic field, which have major influences on climate and such. It stands to reason that we'd be able to find evidence of an event of that scale.

 

#7 If this increase in gravity killed all the large creatures, would it not have largely affected the small as well? An increase in gravity for large beings adapted to low gravity would have analogous affects on small creatures adapted for low gravity, yet they survived, inlcuding the birds, which it seems would have been devestated by a sudden increase in weight.

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...........

 

....................

 

That is the stupidest extinction theory I have ever heard.

 

It's based on *art* not evidence. Let's see what the real evidence has to say.

 

Right after something drastic happened, Pterydactyls were too heavy to fly, and were pinned to the earth.

 

You do realize that most pterosaurs (giants aside) were approximately seagull-sized, and actually weighed about the same? Hollow bones, sometimes nearly paper-thin.

 

Furthermore, there are flying birds both before and after the KT boundary. If there was a gravity increase, we should see different anatomy in the pre- and post- extinction groups (lighter bones, smaller size, etc). We see nothing of the sort. We similarly see no major alterations in flying insects.

 

The brontosaurus could no longer hold up his neck.

 

Aside from the fact that only a few, straggling families of sauropods were even left by the late cretaceous (most had been out-competed by hadrosaurs and other ornithischian grazers), there is similarly little evidence for this as a reason of death.

 

Currently, the main theory on diplodocid biomechanics is that, like gap-bridging snakes, they possessed extremely long tendons that anchored the neck to the spine. They had similar anchors in their tail, which served as a counterbalance. There was little, if any, muscular force involved in holding the neck in position.

 

And, by the way, the average diplodocid sauropod's head was less than 12 feet above the ground. Most of the very-long-necked ones held their necks horizontal, not vertical.

 

Alligators which used to be able to run, were now squashed.

 

Once again, your idea is flatly wrong.

 

1) Alligators can *still* gallop and walk erect

 

2) Genus Alligator (yeah, creative name, huh?) exists on *both* sides of the KT boundary, with NO evidence of anatomical modifications. Ditto for crocodiles.

 

Now, the real killer for your idea:

 

3) Ziphosuchians, the erect-walking crocodylians I spoke of earlier, existed *AFTER* the dinosaurs died. In fact, they enjoyed *much* sucess throughout the world until fairly recently (likely due to climate change).

 

However, there are *also* erect-walking crocodylians from long before the dinosaurs, the sphenosuchians, *and* a group of erect walking archosaurs somewhat closer to (but still before) the dinosaurs, the Erythrosuchids. The former are small sprinters, so don't make a good comparison, but the latter are the spitting image of the post-extinction Ziphosuchians. And they display *no* differences that would indicate a gravity shift.

 

Snakes which maybe used to have tiny legs, learned to slither on their bellies.

 

Snakes *did* have legs at one point. But they lost them 120 mya, almost 60 million years *before* the KT extinction. Things we would recoginze as modern snakes existed 90 mya, 25 million years *before* the extinction.

 

Or were they just really good at anticipating things?

 

Turtles, now took to water to ease the burden of the increase in gravity on their ability to move.

 

Turtles have been around for 200 million years. They have *always* been primarily aquatic. And the largest land-living form, roughly the size of VW beetle, not only lived *after* the extinction, but was killed off by *humans*.

 

Whales used to be able to walk on land.

 

And you didn't read that article, nor do you have any significant knowledge of paleobiology. Want to know how I can say that? Aside from the massive evidence of your ignorance displayed above?

 

Whales lost their limbs *AFTER* the KT extinction. A very Long time after it. Whales evolved from Mesonychids, a group of *erect-walking* mammal predators that looked like wolves, but were closer to sheep in ancerstry. We have a long and beautiful sequence of whale fossils showing the transition from one to the other. All of it is *after* your proposed gravity increase.

 

So, let me get this straight: mammals lived through the KT extinction, into your "high gravity" world, but *still* evolved an upright stance, and then said "Oy, 25 million years of standing up is tiring, let's go back to the water"?

 

Your theory displays nothing but the most superficial and trivial understanding of paleontology.

 

Your grade: F

 

Mokele

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Johnny5

Permanently Banned

 

Awww, and I was hoping he'd get to see his idea's death. Somehow, I don't think I'll miss him.

 

Mokele

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Damn, I was really hoping to reduce him to Jello. Was I right in thinking that Quetzalcoatlus was the last pterosaur? I've read it multiple times, but I can't find the resources I used.

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Was I right in thinking that Quetzalcoatlus was the last pterosaur? I've read it multiple times, but I can't find the resources I used.

 

Well, I don't think it was *the* last, since at any given time there were usually multiple species of pterosaurs in a range of sizes and niches, but, IIRC, it was the last of the truly big ones, and lived right up until the very end.

 

Mokele

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Dont get me wrong -- dinosaurs are hard-core... but i dont think that they could survive the earth being hit by an effing huge metiore' date=' even if theire taxa were in the prime of health and the climate were all hunky-doory for them.

 

Although, having said that, arent crocodyles dinosaurs? which would make the dinosaurs not actually extinct.[/quote']

 

crocs are not dinosaurs, , the only things that survive the "meteor" (if that is wut killed them) was the things that lived under ground or in the depths of the ocean, i learned that in 9th grade, where did you learn your dino history?

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crocs are not dinosaurs, , the only things that survive the "meteor" (if that is wut killed them) was the things that lived under ground or in the depths of the ocean, i learned that in 9th grade, where did you learn your dino history?

Your right, but they both have a common archosaurian anscestry.

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haha... that was actually really funny.

 

just a question (serious one). what was the tortoise that was killed off by humans? and where was it located? or if you have more info...

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just a question (serious one). what was the tortoise that was killed off by humans? and where was it located? or if you have more info...
Well, the giant tortoise Testudo atlas seems to be a possible victim of humans, and i believe it was Asian in the Indian region. A race or two or three of Galapagos tortoises have been wiped out in that particular island chain, with one race represented today solely by Lonesome George, and I'm certain there are others, I just can't remember them.

 

crocs are not dinosaurs' date=' , the only things that survive the "meteor" (if that is wut killed them) was the things that lived under ground or in the depths of the ocean, i learned that in 9th grade, where did you learn your dino history?[/quote'] actually it tended to be smaller species that survived, regardless of their environment, with the great marine reptiles that all dying out as well as the terrestrial animals and the large flying groups.

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ive heard there was evidence of a bug of some kind that killed off a lot of the dinos premeteor. dont ask me to prove it though. weakened animals would have a harder time surviving the event.

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