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Why Did Mammals Survive The 'k/t Extinction'?


Nicholas

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ScienceDaily (Jan. 31, 2010) — Picture a dinosaur. Huge, menacing creatures, they ruled the Earth for nearly 200 million years, striking fear with every ground-shaking stride. Yet these great beasts were no match for a 6-mile wide meteor that struck near modern-day Mexico 65 million years ago, incinerating everything in its path. This catastrophic impact -- called the Cretaceous-Tertiary or K/T extinction event -- spelled doom for the dinosaurs and many other species. Some animals, however, including many small mammals, managed to survive.

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Nicholas,

Here's another example of a science news article claiming something but not really saying anything.

I read science magazines (not all of them and not all of the articles, mostly just the ones that hit me as interesting) and select journal articles plus at least a few mainstream paleo books every year. From what I've read, at first, paleontologists doubted that some asteroid/comet hit the earth but the evidence in favor of it kept coming, so they had to accept it. They wondered, however, about the level of destruction. If it was so catastrophic with all the affereffects (forest fires, acid rain, extreme cold, etc.), how did anything make it through. Of course, it was very popular with TV shows and the public - dinosaurs dying in a huge fireball. It seemed the only thing that could have killed them. Then, scientists thought, "Well, if a meteor hit killed the dinosaurs, the other exinctions might have been caused by them too." They sent teams all over the place and the slightest clue was announced as confirmation.

Then, the partypooper news started coming in. Paleontologists studied the survivors of the K/T extinction and the pattern of survival didn't fit. You'd think anything that lived in trees and on the ground would have suffered around the same percentage. Mammals did survive but in one area of North America, where a decent sample of Late Cretaceous land vertebrates could be collected, one group, the marsupials, suffered the most. Only 1 species out of 11 survived while all 6 of the placental mammal species survived. Five of the ten species of a third mammal group, multituberculates, also survived. How does this fit the linked article? Is the author saying that all but one of the marsupials lived in trees and on the ground while the one that knew howw to swim or hide survived? Most Mesozoic mammals are known only by teeth and jaw sections. Where's the evidence that any burrowed deep enough to escape heat devastating enough to burn all the trees? Did all the placental mammals burrow underground or did they just move into other animals burrows?

The article makes it sound like freshwater was a safe place to live during the K/T extinction except it doesn't mention that all the shark and rays that lived in freshwater also died out. How could mammals but not sharks survive in the same environment?

Paleontologists also pointed out that frogs survived. Only one species was known from the study area but it survived into the Cenozoic. It was not rare and continued to be common afterward. Frogs are rather delicate animals. They are undergoing declining numbers worldwide now but there has been no fireball - just the cumulative result of pollution and habitat loss.

The other bad news for the asteroid fans was that with all the interest, other impact sites were discovered. Some of these impacts were almost as sizable as Chixulub but they took place at a geologic instant when there was no associated extinction. Furthermore, initial reports of confirming evidence of impacts associated with other mass extinction events offered results that could not be duplicated by additional studies. A large crater that was dated as having formed near the end of the Triassic, when there was another mass extinction, turned out to be 13 million years too old to have had an effect. Keep in mind that the tools used to determine the age of rocks have gotten more precise and with smaller margins of error over the past couple of decades. Chixulub was confirmed but then evidence was offered that there may have been two impacts within a million years, a level of resolution that was not possible to read thirty years ago.

What I'm saying is that this is a complex issue but the average science article tries to whittle a story down to a few paragraphs with no room for opposing evidence if the story is too fanatastic. I've also read that physicists staunchly defend the "asteroids kill everything" theory while paleontologists wonder how frogs lived through fire.

Two books to read that offered background on this are:

Archibald, J. D. 1996.

Dinosaur extinction and the End of an Era: What the Fossils Say.

Prothero, D.R. 2009.

Greenhouse of the Dinosaurs: Evolution, Extinction, and the Future of the Planet. (Chapter 5).

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Trust me I know the irritation of science media, and I thank you for the clarification. In my field I constantly roll my eyes over the articles being reported usually nothing of substance or distorted meanings... and some times old news revisited.

I post these articles not because they are good, sometimes they are, but they usually promote great discussions and answers like yours. :P

Again thanks for telling us the difference.

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Yeah that article says a lot of thigs that are untrue or make no sense logically. I wonder if it wasn't written by a High School student with only minimal outdated knowledge.

The last research I've heard was that the number of dinosaur species was in rapid decline before K/T. Gerta Keller has evidence that the Chixalub impact was in fact maybe 500k years seperated from the actual K/T "event" (as recorded by microfossils and strata).

If there was a massive die-off caused by some massive meteor or large scale forest fires then where are the charred herds of dinosaurs?

I'm starting to wonder if there wasn't also some sorta mystery virus or bacteria that mainly affected the higher-metabolism reptiles (dinosaurs, pterosaurs) but spared the lower-metabolism reptiles (snakes, crocodiles, turtles, lizards) and amphibans.

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it is my sense that any "straightforward", pablum-for-the-masses attempt at explaining or understanding global extinction events necessarily ignores the almost unlimited variables involved in global ecosystems and therefore represents an intellectually dishonest major "fail". the initial, convenient premise that any one given factor was causative seems a huge leap in logic, and similarly, any conclusion that various organisms went extinct globally due to identical causation is an unnecessary, although comfortably simplistic, way to view the thing.

i feel that even the wikipedia article on the subject makes a much better attempt at pointing out the complexities and uncertainties of the matter. later, K-taters

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The last research I've heard was that the number of dinosaur species was in rapid decline before K/T. Gerta Keller has evidence that the Chixalub impact was in fact maybe 500k years separated from the actual K/T "event" (as recorded by microfossils and strata).

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####There are also studies that show species were every bit as numerous and vibrant immediately before K-T as ever

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If there was a massive die-off caused by some massive meteor or large scale forest fires then where are the charred herds of dinosaurs?

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####At any one time, there are relatively few large organisms living. If there was a meteor impact, with an initial ash producing fire blast, followed by acid rain, why would fossilization occur? Don't forget, there is a demonstratable spike in spore count, they were feeding on something.

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I'm starting to wonder if there wasn't also some sorta mystery virus or bacteria that mainly affected the higher-metabolism reptiles (dinosaurs, pterosaurs) but spared the lower-metabolism reptiles (snakes, crocodiles, turtles, lizards) and amphibans.

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####You mean like mammals? We really don't know much about amphibians, particularly frogs. The number of amphibian fossils wouldn't fill a five gallon bucket, hard to make claims based on what they did. While being delicate, they tend to burrow into the mud, good protection from blast, and also seemingly making them better subjects for fossilization, maybe they were actually quite rare in the environment, but because of their habits, fossilized at a higher rate?

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In major extinction events, I am a catastrophist. It is my opinion that organisms can adapt rapidly to a changing environment. Whatever happened (in my opinion) was sudden, savage, and probably measured in minutes. There have been at least 5 major extinctions, I suspect there was also one immediately proceeding the "Cambrian Explosion". Of these, the only one that is easy to explain is the end-Ordovician, where an ice age caused drying of shallow ocean environments. Was it even a true mass extinction? If the same situation happened today, I doubt it would be considered such. We would actually see an increase of land species, as habitable land increased.

Bakker pointed out these facts about mass extinctions:

-Kills on land and sea at the same time

-strikes hardest at large fast-evolving animals

-hits small land animals less hard

-leaves large cold blooded animals largely untouched

-strikes plant eaters more severely then plants

An explanation has to cover all of these facets, whether one cause or several. Keep Occum's razor in mind when you start lumping possible causes together, because your explanation becomes less an less likely which each "and this also happened"

This is an interesting topic, one we have hashed before, and will hash again, no doubt.

Brent Ashcraft

ashcraft, brent allen

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Yeah that article says a lot of thigs that are untrue or make no sense logically. I wonder if it wasn't written by a High School student with only minimal outdated knowledge.

The last research I've heard was that the number of dinosaur species was in rapid decline before K/T. Gerta Keller has evidence that the Chixalub impact was in fact maybe 500k years seperated from the actual K/T "event" (as recorded by microfossils and strata).

If there was a massive die-off caused by some massive meteor or large scale forest fires then where are the charred herds of dinosaurs?

I'm starting to wonder if there wasn't also some sorta mystery virus or bacteria that mainly affected the higher-metabolism reptiles (dinosaurs, pterosaurs) but spared the lower-metabolism reptiles (snakes, crocodiles, turtles, lizards) and amphibans.

re: fire - lots of theories and arguments -- this is from a post last month-

Dinosaurs broiled, not grilled

Debris from K-T impact could have been heat source and heat shield

Ultimately, the Earth’s surface still felt like an oven on broil, but for only about eight minutes, the model suggests. The surface felt less heat for less time. This could explain why the species that survived the impact included small, burrowing mammals and aquatic reptiles like crocodiles that could take shelter from the searing heat, says Doug Robertson of the University of Colorado at Boulder.

“I’m really pleased about the model,” says Belcher, who says her research on the charcoal content of the boundary layer argues against widespread wildfires. “I think it’s been a long time coming.”

Robertson still believes worldwide fires occurred, however. While the radiation may not have been enough to directly ignite wood, it could still have kindled pine needles and dry leaves, he points out.

“You don’t need to ignite every tree to have a forest fire,” he says. “Toss a smoldering cigarette—it won’t ignite a log either, but it will ignite a forest fire. It’ll hit dry leaves, and poof.”

“It’s not a closed book on the wildfires,” Goldin says. “There’s still a lot of work going on, on both sides on this story, to converge on a solution.”....

Friday, December 11th, 2009

http://www.sciencene...nosaurs_broiled,_not_grilled

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A few points - in order to infer a catastrophic extinction, you need evidence. Now, someone (lance?) mentioned above "fields of charred dinosaurs", and some folks have said 'well, where are the piles of dino corpses at the K/T boundary?'

The problem is that in order to preserve any evidence whatsoever of an event like this, deposition of sediment is required. In the case of the terrestrial realm, sea level was relatively low (and dropping) at the end of the Maastrichtian; during a 'base level' fall, downcutting and erosion increases, and deposition of sediment decreases. This is why so few terrestrial rocks worldwide show any evidence for the event, or even the K/T boundary and the iridium anomaly itself, for that matter. In fact, the reason why the hell Creek Formation is so famous (aside from T. rex and Triceratops) is because it is one of the few fossil-bearing terrestrial rocks that preserves the boundary itself. Now... generally fossilferous rocks are deposited during lower rates of sedimentation (lower sediment deposition rates lessens the dilution of fossils within the environment). Although lower sedimentation rates are conducive to preserving and accumulating vertebrate fossils... any notion of a boundary layer has a high chance of being destroyed by erosion. Which is why the "Z-coal" (lithostratigraphic "marker" of the K/T boundary) only appears in some places. Additionally... the hell Creek Fm. has different thicknesses, and the "z-coal" is geochronologically slightly younger or older than the actual chronostratigraphic K/T boundary... so it is extremely difficult to point to the KTB and say "this dinosaur bone right below it means the dinosaur died during the impact event". That bone could be transported there or eroded from older sediments, or could even be just a few months older.

The resolution of the terrestrial vertebrate fossil record is too poor to discriminate between catastrophic or gradual decline. Additionally, there is the added problem that no dinosaurs have actually been found within 3 meters of the K/T boundary in much of MT. Elsewhere, where the hell Creek is of a slightly different age, there is actually an articulated Triceratops skeleton that has been found above the K/T boundary, in the Fort Union Formation. Is this a case of a dinosaur that survived the extinction??! No... the age of the Fort Union Formation just happens to be cretaceous in some areas, because terrestrial sedimentary rocks can vary in age laterally almost as much as they can vertically.

The entire problem here is that there is virtually no way of knowing, independent of the serious flaws in catastrophic 'models' constructed thus far. Other important things to remember are: 1) dinosaur diversity was seriously dwindling by the end of the Maastrichtian; relative to the Campanian (e.g. Dinosaur Park and Judith River/Two Medicine Fms.) diversity had decreased by 2/3. Keeping in mind that Torosaurus and Triceratops, Pachycephalosaurus/Stygimoloch/Dracorex and T.rex/Nannotyrannus are all just ontogenetic morphs of the same species, that effectively takes seven species and reduces it to three. 2) There is no 'clear' segregation between survivors and the extinct. Not via body size, reproductive strategy, and certainly not physiology, as this study seems to promote. What about birds? Birds are warm blooded, and they survived too - but most birds are not fossorial. What about small dinosaurs? They get killed off too. And now we even have burrowing dinosaurs! There is even evidence to suggest many small bipedal ornithischian dinosaurs were burrowers, and many more dino burrows have been discovered since on different continents.

Anyway, just some pertinent info.

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i still say i want to be like bobby when i grow up...i can see little muscles on his iq nodules.

one thing nobody seems to point out about birds (and hopefully auspex won't jump on me here and point out that i'm full of the proverbial crabs), is that birds can fly away.

it would seem to me that, if you picture your average "negative situation", with you sitting there, waiting to be extinctified, you're not gonna have many birds sitting there with you. they'll look at you, laugh in their completely annoying bird manner, and fly away, likely dropping a wet, white one on your forehead as they go.

where do they go? i'm never sure, but undoubtedly, to places where they have those little unbrellas in the drinks.

very few cataclysmic events would equally and homogeneously affect all areas of the globe. relative mobility would therefore be one of the many variables to consider, along with resource needs, etc. another point is that some critters can only survive within narrow ranges of parameters. (like me). other critters can apparently survive anywhere and everywhere, as long as there is rock dust for them to breath. (like rb). you see this modernly with plants and critters - some things live everywhere, and some things just live in a weensy locale where the pillows are fluffed hourly. don't know why; just how it is.

there was a point in my brain somewheres....hmmm...i'll go look for it.

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As far as birds, I read a study at one point where most modern birds are descended from Asia, as I recall they speculated that was because they had a higher survival rate after the meteor impact then their N. American relatives.

I don't know if I agree with the morphs of the same species argument as reduction to diversity. If you look at ruminants today, you could argue that they are also morphs of the same species, but they are pretty diverse.

More info for the fire pit

Brent Ashcraft

ashcraft, brent allen

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