Cretaceous extinction

[Slypork]

My 14 year old son and I were watching some Discovery Science program about dinosaurs and it mentioned the theory that an asteroid or other “cosmic event” triggered their extinction. This seems plausible enough if you examine the evidence of the KT boundary and the Chicxulub Crater.
Then my son asked, “OK, I can see why the big sauropods died and even the bigger flying reptiles like pterodactyls and even the big swimming ones like the plesiosaurs. But why did the smaller ones like compsognathus die off? Shouldn’t they have been able to scavenge off the carcasses? What about the other marine creatures? Why couldn’t they survive? If the event changed the climate and cooled everything off so cold-blooded creatures had problems, how did that effect the marine creatures? I mean, sharks and fish aren’t warm blooded so they should have died off, too.”
I love my son but he is too damn smart for his own good. Not wanting to look like a total idiot I told him, “They all died off because God didn’t want them around.”
Kidding!! Actually, I told him I didn’t know why certain species died off and others didn’t but I knew just the right group to ask.

So, to all of you paleontologist, archeologists and dino-nuts on the SDMB: Can you explain why only the sauropods and their dino-like cousins died off and other creatures did not?

[carnivorousplant]

@erie774

Shouldn’t they have been able to scavenge off the carcasses? What about the other marine creatures? Why couldn’t they survive?

The bodies would begin to rot. The sea depends on sunlight for the food chain.
I’ll just hang out and wait for someone who knows more than I to show up.

[Musicat]

Just how long do you think carcasses will last? After the first few weeks, what do you do for food for the remaining, oh, say, million years or so? Even 7-11’s need to be resupplied sometime.

There’s not one single answer to your question, although there are several theories, and here are some of them: National Geographic

"Another important factor is that the Yucatan, where the giant asteroid hit, was especially rich in sulfur-bearing rocks (calcium sulfate). The impact vaporized the sulfate rock and deposited billions of tons of sulfur dioxide gas in the atmosphere.

“Studies of volcanic eruptions have shown that this gas would convert to sulfuric acid clouds in the atmosphere, and that such clouds could remain in the atmosphere for years. These clouds may have initially been thick enough to shut down photosynthesis for a year, and perhaps they blocked the sun long enough (several years) to cause major global cooling. This mechanism helps explain why the impact was especially devastating,” Pope says.

New Dino-destroying Theory Fuels Hot Debate

Most dinosaurs were incinerated in a matter of hours after an asteroid impact 65 million years ago kicked up a global rain of broiling debris, according to a new study.

Anything not underground or protected by water was wiped out.

The research builds on previous studies that concluded the die-off was rapid. The new analysis presents a plausible scenario of swift death, outside experts said, but they caution that the fossil record for an event so long ago cannot discern whether the extinction played out over hours or years.

For more than a decade, most researchers have been convinced that an asteroid was responsible for the death of the dinosaurs. Recently however, a handful have argued that a combination of effects – an asteroid along with perhaps increased volcanic activity and climate change, or even a second asteroid – caused a slow demise of the giant animals…

http://www.priweb.org/ed/ICTHOL/ICTHOLrp/19rp.htm

Alvarez’ hypothesis has been altered to include everything from massive wildfires to global volcanic activity but most scientists now agree that some sort of wintry darkness was the cause for the ultimate demise of the dinosaurs…

http://www.newton.dep.anl.gov/newton/askasci/1995/environ/ENV182.HTM

Global warming triggered the worst mass extinction in the Earth’s history some 250 million years ago, according to a computer model of the climate during the great prehistoric die-off.

http://www.isgs.uiuc.edu/faq/dino-faqs/pdq85.html

A brilliant flash erupted in the southeast as the asteroid rammed into Mexico’s Yucatan Peninsula, gouging out a crater about 120 miles wide and vaporizing the upper crust.

A brilliant, hot plume of vapor and incandescent “sun-bright” debris arced across the sky at about 7 to 10 miles per second, then crashed onto North America.

Scalding heat killed countless land-dwelling plants and animals. For example, 90 percent of known types of leaf-bearing trees and plants became extinct, according to the fossil record.

[Slypork]

@Musicat

Just how long do you think carcasses will last? After the first few weeks, what do you do for food for the remaining, oh, say, million years or so? Even 7-11’s need to be resupplied sometime.

There’s not one single answer to your question, although there are several theories, and here are some of them:
<snip>

New Dino-destroying Theory Fuels Hot Debate | Space

I understand that bodies wouldn’t have been around forever, but as the larger creatures started dying off there would still be some T-Rex Tasties ™ around. And the little scavangers could have been eating shrews, voles and marmosets thus preventing the evolution of Pauly Shore. Surely some of them could have survived unless there was a dino-specific reason (and don’t call me Shirley)
That cite mentions being protected by water. So what the hell killed off the plesiosaurs? Was it the massive wave from the asteroid hit making them surf to Europe? Or did it superheat the water to a point where the larger creatures got boiled off but smaller ones didn’t?
Sorry if this seems sort of smart-assy but I’m really curious. The land extinction I can see, but not the sea extinction. See?

[CalMeacham]

Nitpick: Compsognathus was Triassic. I think they were long gone by the time of the Cretaceous extinction.
IIRC there were a lot of marine extinctions of non-large animal life .The problem is, I know my memory plays me false on some of these, but I believe that there was a big drop, for instance, in Ammonites (octopus-like creatures living in spiral shells, like the present-day Chambered Nautilus), Belemnites (same thing, only straight shells), and others. why? They were pretty commonplace around the world.
It’s not clear to me why plesiosaurs and ichthyosaurs should’ve died off. Some of them were relatively small. Ditto on the Pterodactyls – most such flying reptiles were small. Quetzalcoatylus gets all the press because it was so big, but the majority of specimens of flyers – Rhamphoryncus and other multi-syllabled named ones were bird-sized (albeit large birds). (And, of course, neither the flyers nor the marine reptiles were technically dinosaurs.)

[Colibri]

@erie774

I understand that bodies wouldn’t have been around forever, but as the larger creatures started dying off there would still be some T-Rex Tasties ™ around. And the little scavangers could have been eating shrews, voles and marmosets thus preventing the evolution of Pauly Shore. Surely some of them could have survived unless there was a dino-specific reason (and don’t call me Shirley)

Many small dinosaurs did survive the K-T event. We call them birds.

Extinction is chancey during a catastrophe like the one that ended the Cretaceous. Because it completely disrupted local ecologies, it preferentiall killed off the larger land creatures, all of which were dinos. It also probably killed off most of the smaller creatures as well; but a few of these survived, including small mammals, birds, and smaller reptiles and amphibians. It may have just been coincidence that non of the smaller non-avian dinosaurs survived.

That cite mentions being protected by water. So what the hell killed off the plesiosaurs? Was it the massive wave from the asteroid hit making them surf to Europe? Or did it superheat the water to a point where the larger creatures got boiled off but smaller ones didn’t?
Sorry if this seems sort of smart-assy but I’m really curious. The land extinction I can see, but not the sea extinction. See?

The evert disrupted oceanic ecosystems as well. It probably wasn’t due to heating per se, but due to changes in chemistry of the surface waters such as acidification. Many kinds of plankton, such as the giant Foraminifera, also became extinct at the same time. This would have caused starvation of the smaller fish that fed on them, with effects that extended on up the food chain. As on land, the animals hardest hit were the largest ones, including the plesiosaurs, mosasaurs, and ammonites (cephalopods).

[Darwin_s_Finch]

@erie774

So, to all of you paleontologist, archeologists and dino-nuts on the SDMB: Can you explain why only the sauropods and their dino-like cousins died off and other creatures did not?

That is, in fact, one of The Big Questions in vertebrate paleontology. You may (or may not) be interested in this earlier thread on the topic. There’s a lot of good info there, both on what lived and what died, as well as the miscellaneous global goings-on at the time that helped to spell doom for those critters.

[Lemur866]

Cold blooded reptiles preferentially survived the KT extinction. Turtles, lizards, crocs and such made it through. Warm blooded dinosaurs and other archosaurs died, except for a few branches of small feathered dinosaurs. Ammonites died out.

During the Cretaceous there were fewer fish than nowadays. The oceans were full of marine reptiles and ammonites that were largely replaced by fish and to a smaller extent by marine mammals.

[Grendel_s_Father]

One important thing to remember is that not all big prehistoric reptiles and dinosaurs lived at the same time. As has been mentioned, Compsognathus was earlier (Late Jurassic though, not Triassic), and as about as distant from the K/T extinction as you are from T. rex. Many major dinosaur groups were gone or on the way out by the end of the period. Pterosaurs were almost all gone–all that remained were a few types of giant azhdarchids like Quetzalcoatlus, the ones in niches that hadn’t been taken over by birds already. Ceratopsians and hadrosaurs are the only groups that really seem to have been widespread and diverse at the time of the extinction, off the top of my head.

All the small dinos at the time were feathered, winged species that would be called “birds” outside a technical sense (dromaeosaurids, troodonts, etc., plus the last ornithomimids, which were primarily herbivores). Why some bird groups died off and modern toothless groups didn’t is a mystery, as far as I know. I’ve heard that modern birds were mainly in shorebird niches at the time, which tend to be more resiliant and numerous (anyone taking bets on what birds would survive a mass extinction today should look at seagulls).

As for the marine species, most theories I’ve heard deal with the death of lots of types of plankton, which would majorly mess up the marine ecosystems in any time period. The extinction of the exremely numerous and diverse ammonites probably had a whole lot to do with the extinction of all the large marine reptiles as well.

[Polycarp]

There were several events in the Late Cretaceous that may have contributed to the K-T mass extinction. The Chicxulub meteorite was unquestionably a significant factor, and probably “the last straw” in terms of being the proximate cause. However, two or three other events, depending on how closely you see them associated, were involved.

1. The Laramide Revolution had been going on. The fertile low plains of Colorado, Wyoming, Utah, Montana, and Alberta, with intermittently an inland seaway, were colliding with what had been offshore island terranes on another plate, and being replaced by the Western Cordillera – the Rocky Mountains and all the related ranges that extend west through the Basin and Ridge geomorphic Province. Dinosaurs were able to adapt to this, but with some significant shifts in populations. Outside Mongolia, there were only 13 families of dinosaur worldwide in the last stage of the Cretaceous. (Relate this to present megafauna – rhinos and elephants continue to thrive, but as only a few species compared to a diverse population before and during most of the Ice Age.)

2. India, still an island continent, was passing over the Seychelles hot spot, one of the areas where magma is being upthrust. The result was the Deccan Traps, something people outside the interior Northwest will not be familiar with, but the simplest description would be non-mountainous vulcanism – massive amounts of lava flooding out of vents to cover large areas of land – with consequent releases of noxious gas and particulates. Anyone familiar with the effects of the Tambura eruption (“the year without a summer”), and the lesser but real effects of Krakatoa and Mount Saint Helens, will be aware of the potential for significant large-scale climate change from such events. Now imagine a non-point source producing at about the quantity of 100 Tamburas over years or centuries.

3. There appears to have been a sharp change in global climate toward the latest Cretaceous – a global cooling. To what extent this is related to #1 and #2 and to what extent an independent development is grist for some serious argument.

The K-T extinction, though, was not confined to the dinosaurs. Numerous families of plankton were driven extinct by whatever cause(s) the K-T event is attributed to. And the impact of this spread across the entire metazoan (multi-celled animal) subkingdom.

The ammonites (equivalent to the chambered nautilus), a major element in the Cretaceous oceanic fauna, went extinct. The belemnites, effectively squids with shells or tests, likewise. The brachiopods, until then the dominant bivalve shellfish, survived but lost their dominance to the pelecypods (clams, oysters, mussels, and their kin), becoming a relatively minor constituent of the ocean-floor fauna. Crinoids became significantly rarer. The same story could be told for most of the invertebrate phyla that left enough fossils to make the determination. The coelacanths, common in the Cretaceous, became so rare that they were thought extinct until the chance discovery of Latimeria in 1938.

Among the vertebrates, the pattern is checkered, and appears to have selected against high-metabolism large animals without “pelt” (fur, feathers, whatever besides fatty tissue and thick skin keeps one warm). If you were high-metabolism but with insulating cover (birds, mammals) or low-metabolism and small, you had good odds to survive. Michael J. Benton’s The Fossil Record 2 gives the following statistics for vertebrate extinctions (format is number of families extinct after the K-T event out of number of families in the Maastrichtian, the last stage of the Cretaceous, and percentage extinct):

Sharks, rays, and chimeras: 8 of 44, 18%
Bony fish: 6 of 50, 12%
Amphibians: 0 of 11, unscathed
Turtles: 4 of 15, 27%
Lizards and snakes: 1 of 16, 6%
Crocodilians: 5 of 14, 36%
Pterosaurs: 2 of 2, 100%
Dinosaurs: 21 of 21, 100% (8 of these families are known only from Mongolian deposits that are not certainly Maastrichtian, so the more accurate figure may be 13 of 13)
Plesiosaurs: 3 of 3, 100%
Birds: 9 of 12, 75% (This figure may not be accurate, as there are Cretaceous fossils debatably assignable to surviving groups not taken into account here.)
Non-therian basal mammals: 1 of 11, 9%
Marsupials: 3 of 4, 75% (the surviving family is Didelphidae, the American opossums)
Placental mammals: 1 of 7, 14%

[Slypork]

Damn! You are some smart people! Thanks for the info and insight. I knew I’d get some reasonable explanations from this crowd. I really appreciate it.