Dinosaurs, Mammals and survival at the KT boundary

I see that.

But some of the small things died as well. In particular, ALL the small dinosaurs died. It's those I'm trying to figure out. They weren't significantly different from birds or mammals, and yet THEY died, but many types of birds and mammals didn't. What made the difference?

I hope I dont attract the "troll", if I do, Ill just drop out and read

Dinosaurs dont have to be thought of a s strictly reptilian but a modification that had a number of varying features. In fact, there is no subclass or order of "dinosaur" only
reptiles of the superclasses
synapsida
Parapsida
Eurapsida
Diapsida(which included a number of suborders of other reptiles including)
Archiosauria(whch contain orders of other reptiles)
Pterosauria
Saurichia
Ornithischia

The last theree orders contained the dinosaurs. I purposely omitted all the other reptiles except those that had direct linneage relationships to the dinosaurs. The subclass synapsida and the order Therapsida had over 7 superfamilies of mammal -like reptiles


The classical classification is being abandoned in favor of more linneages that recognize that orders had evolved and then continents split apart and some floated away and adapted(and changed) to address a host of other environmental conditions like some duckbills in the Antarctic were very different from those in the US . Some workers think that Maybe they should be classified more by those cosequential adaptive differences. (Antarctic was arboreal almost Arctic in the K- maybe these dinosaurs used torpor like bats do for adapting to winter )


However Not all the mammals made it through the KT boundary, only the multituberculates, the monotrema, the pantotherians, and the placentals (the marsupials didnt evolve till later) the other 5 orders got whacked . The KT boundary was , as had been mentioned, perhaps a variable localized type of killer.
No evidence of rapid occurence of reducing conditions (like wed expect in a super volcano or large shield volcano swarm) . The rocks in the KT just go on as if nothing happened for most of the world. The "iridium layer" occurs at the very top of the terminator and the dinosaurs die out much earlier so a new theory has arisen about multiple terminators, or climatological change

I personally like Dave RAup's personal theory
Dinosaurs died out for 2 reasons
1It was a dumb idea to start with
2 It had gone on quite long enough


Dinosaurs were already dying out well before the KT. In fact at a GSA meeting last week we had a very lively discussion of evidence that showed the Chixclub event post date the dinosaur terminator by a few 100 millenia. The argument is that there is a "double " terminator like at the Permian.

North America had a shallow sea in the middle so the Great Lakes are remnants of the shallow sea. It is this shallow sea that had forested banks on which the dinosaurs lived. When the sea bed rose the remains of the dinosaurs ended up in places like Wyoming, Alberta where the dryness probably preserved their carcasses from further deterioration. The scale DNA can be converted to either hair or feather.

Asteroid (12 miles in diamter) vaporized: See here

Paleogeography of the Great LAkes is more related to glacial erosion of the mid arch and not a remnant of the Triassic to paleocene synclinal sea. In the K the sea reached its maximum by splitting the Western foreland from the Eastern paleoAppalachian terranes. The evolution of the major groups of reptiles, birds, and mammals had occured in the Triassic before Laurasia began to split(therefroe most animals are related by virtue of pre Jurassic association from US through Asia.

Heres a NOAA account on the paleogeography of the Great Lakes

Stuh, "I don't think so" was about feathers needing to evolve from hair. I'm not certain, but here's the result of a quick search:

http://dml.cmnh.org/1995Jan/msg00270.html

Love it when farmerman checks in for these subjects, great stuff.

So it could be basically just that the dinos were too goofy to survive?

It took only 5 million years for humans to evolve.

The dinos had 70 million years. By this time they would be very well perfected to their environment, and wouldn't just start dying out for no reason!

Unless the environment changed. Maybe they were so perfected to their environment compared to other animals that the reason they weren't able to survive is that they were too specialized, too niche, not adaptable enough at that point in their evolution. Dunno.

By the way I was (mostly facetiously) paraphrasing what farmerman was saying. I'm interested in getting more about that out of him. (Also about the "double" terminator.)

There he goes. One of God's own prototypes. Some kind of high powered mutant never even considered for mass production. Too weird to live, and too rare to die.

Soz, Dave Raup is the compleat scientist. He has his good stuff and he readily admits to his bads. Hes got a sense of humor like Dave Barry and a curiosity that has allowed him to address the big questions of evolution by going backwards and looking at the roles of mass extinctions and how theyve provided the available responses by the evolution of newer species and entire genera. He wrote a great little book back in the 80's called "Extinction, Bad Luck or Bad Genes". In it he takes the concepts of statistical testing and rules of gambling where subsequent moves are dictated by the cards that have already been played. (Counting techniques and "gamblers ruin)

I always thought that his explanation regarding the end of the dinosaurs means as much as anything.
Dinosaurs werent necessarily goofy, just really well adapted. Theres another line from the role of extinction it says that "Any being so well adapted to its environment is also held prisioner to it".In other words, change the environment too much and too quickly and its a recipe for extinction. For guys like me its great, approximately 99.9999% of all the animals that ever lived are extinct and most have left good guide fossils that we often use as "roadmaps to exploration"

I agree with the concept of this statement, but I'm not convinced of its application to reality in the case of the dinosaurs.

Dinosaurs were very diverse. I'm sure some were specialized and overtly succeptible to change, especially the large ones. But I get the impression that many were very robust, complete with a long line of 'junk' DNA to fuel variation when necessary. This did not appear to be a fragile class of animals. They had the ability to adapt just as fast as anything else (or at least, I assume they did. If someone told me they didn't, then it might answer my original question).

Were there ANY dinosaurs which lived a subterranean lifestyle? Many mammals and reptiles live underground.

Was there anything unique about the particular mammals which did NOT survive the KT boundary?

Farmerman: Thanks for the Great Lakes stuff. Lot of stuff I write from the top of my head. Paleontology and rock science ain't my field just hobbies.

The weaknesses would be the eggs, size, diet and body plan. Eggs with hard shells are susceptible to breakage; size means quick starvation if there is a drought, fire, disease or just over population whereby food source becomes scarce; diet - if they eat only certain foods and not adapt then they will starve just like the panda bears that eat only leaves of certain trees; and finally the body plan limits certain activities. T Rex has adapted so well to hunting slow moving sauropods that its forearms shrivelled to mere ornamental attachments. It can't climb trees anymore. It wasso easy chasing sauropods that its brain did not develop for more complexactivities. It reminds me of the electronic word processors and type writers that died as computers took over because it was multi-functional.

talk, there we go, those are examples of what are those little things that host extinction in a normal fashion. As the environment of the K changed before the MAastrichtian epoch, most of the plant eaters were already dwindling. Another "excuse" is that the rise of angiosperms happened about the same time and angiosperms ability to conserve energy bu going to seed and then drying up the plant mass can be another example of "too fine an adaptation'. The plant eaters were used to bulking up on cycads and tree ferns in the tropical climate, when it turned temperate arid theybegan to go extinct and meat eaters like T-Rex became deprived of abundance.

ANother raeson, and maybe its not too obvious, is that most dinosaur genuses had only one or two species and RAups rule for avoiding extinction is to have built in diversity by having many species in your genus (mice have over 200, so while some may die, many will make it through)

Some reptiles, like the Theriodonts and the synapsids , DID live underground and then survived the Permian extinction and became mammals.
This is not my major field and most paleontologists who work on dinosaurs are rather a bunch of people who, In my estimation, couldnt escape a burning building without further data. When oil companies want to commence drilling they usually hire guys like me (with a bit of ADD and senses of urgency) to herd the paleos into getting to a point. The simple fact is that dinosaurs have only interest in academics and entertainment. They have little commercial value for guide fossils. Most index or guide fossils are marine ones that lived for brief periods but had wide ranges. We use foraminiferans for more than just a great breakfast cereal.

But the fact that most dinos species were alredy gone before the end of the K was brought out by the GSA last week. Raup used his examples of the parallel to trilobites, in the Cambrian and ordovician, there were thousands of trilobite species. These dwindled down to a few hundred by the Devonian mass extinction (the evolutionary trend was toward spinosity-perhaps a s a strategy to protect against the rise of fish). Then , by the end of the Permian at the really big extinction, they were down to lessthan 20 species and then they were gone by the end of the Permian. They were in the process of going extinct but the Permian terminator (vulcanism) hastened the job.

However, the dirty little secret of systematics is that we define major faunal epochs based upon extinction and appearances . In other words" dinosaurs died by the end of the K because we defined the end of the K based upon the death of the dinosaurst" The fact that we give it a fancy name for the "Chalk seas" is more coincidental . the Cenozoic was based upon the rise of many new species i the PAleocene fossil record.

Bigness has always been a problem for longevity in all orders, Its an example of close adaptation and morphlogical response. The big bugs of the CArboniferous were used to having high O2 levels and they were quickly decimated in favor of smaller mass insects able to respirate at 20% and lower O2, as the O2 levels were declining through the PErmian and into the Triassic/ So, also, megafaunas of the Cenozoic were a particularly bad example of " experimentation gone wild". The megafauna appeared and disappeared quickly and the rapid climate changes that started after the Miocene were probably a added reason. So, as "the present is key to the past" except when theres a really weird one time event, still holds. But the major exterminations were tied to many of these speciic environmental catastrophes or major changes in feedtock strategy.

Oooh, this is great. Makes a ton of sense.

I pmed Gus and he told me.

I am not satisfied with the explanation that the asteroid hit at a "shallow angle" as the impact crater is circular thus it was at a near perpendicular hit. If it was at a shallow angle the crater would be a parabola. Also the Deccan Traps were active at the same time so there was penetration of the crust. As the asteroid hit near the equator most of the big dinosaurs lived in warm forested areas so the devastation would be felt most by them. North America was affected as there was a shallow sea in the middle so the tsunamis would have travelled right up to the Hudson Bay with little or no hindrance.

In 1990 a scientist called Alan Hildebrand was looking over some old geophysical data that had been recorded by a group of geophysicists searching for oil in the Yucatan region of Mexico. Within the data he found evidence of what could have been an impact site. What he 'found' was a ring structure 180km in diameter which was called Chicxulub. The location of this structure was just off the northwest tip of the Yucatan Peninsula. The crater has been dated (using the 40Ar/39Ar method) as being 65 million years old. The size of the crater is comparable to that which would have been caused by an impacting body with a diameter of roughly 10km.So we now have some of the proof of the asteroid theory. We know that a chondritic meteorite with a diameter of 10km contains enough iridium to cause a spike. We also know that about 65 million years ago there was an impact of a large object. The big question is what were the results, and how did they effect the dinosaurs.
In 1990 a scientist called Alan Hildebrand was looking over some old geophysical data that had been recorded by a group of geophysicists searching for oil in the Yucatan region of Mexico. Within the data he found evidence of what could have been an impact site. What he 'found' was a ring structure 180km in diameter which was called Chicxulub. The location of this structure was just off the northwest tip of the Yucatan Peninsula. The crater has been dated (using the 40Ar/39Ar method) as being 65 million years old. The size of the crater is comparable to that which would have been caused by an impacting body with a diameter of roughly 10km.So we now have some of the proof of the asteroid theory. We know that a chondritic meteorite with a diameter of 10km contains enough iridium to cause a spike. We also know that about 65 million years ago there was an impact of a large object. The big question is what were the results, and how did they effect the dinosaurs.




The Yucatan Peninsula



A map showing the probable location of the crater formed by the impact of the K-T meteorite.

Chicxulub, Yucatan Peninsula, Mexico
This three-dimensional map of local gravity and magnetic field variations shows a multi-ringed structure called Chicxulub named after a village located near its center. The impact basin is buried by several hundred meters of sediment, hiding it from view. This image shows the basin viewed obliquely from approximately 60° above the surface looking north, with artificial lighting from the south. (Courtesy of V. L. Sharpton, LPI)
If a 10km diameter object impacted at the point at which it struck it would have a velocity of roughly 100,000 km/h. At this velocity there would have been an initial blast (with an estimated force of many millions of tons of TNT) which would have destroyed everything within a radius of between 400 and 500km, including the object. At the same time large fires would have been started by the intense shock wave which would have traveled long distances. Trillions of tons of debris (dust, gases and water vapour) would have been thrown into the atmosphere when the object vaporized. Many enormous tidal waves would be started causing even more damage, the evidence of such waves has been found all the way round the Gulf of Mexico. Along with the tidal waves the blast would also start a chain reaction of earthquakes and volcanic activity there would have also been very high winds caused by the blast. In the days and weeks following the impact the cloud of debris would have been carried over large distances by the post blast high winds. This will have caused months of darkness and a decrease in global temperatures. After this there would have been an increase in temperatures caused by the large amounts of CO2 released by what would have been global fires. Eventually this would cause chemical reactions that would result in the formation of acid rains.



Dino Killer?
An artists impression of the meteorite that was responsible for the death of the dinosaurs.
Artist: Don Davis (No Copyright-see NASA "USE" policy)
On the land the effects of the impact on the flora and fauna would have been devastating, especially on the large animals which would need large food supplies and on the dinosaurs which would need sun light to keep warm. The global fires would have destroyed considerable amounts of vegetation (by the analysis of the soot in the K-T boundary it is estimated that 25% of the vegetation cover was destroyed), the immediate effect of this would have resulted in the death of the large herbivores. A knock on effect of this would have killed off the large carnivores. Only the small active scavengers, like birds and mammals with the ability to find food from a wide range of sources would have survived. Analysis of the K-T boundary fossils shows that there was a short term takeover of the land by the hardy ferns, which moved into the areas were there had been fires.
In the sea the effects would have been just as dramatic. There would have been a decrease in the oxygen levels in the seawater as low oxygen deep seawater would have been brought up by massive under water currents. This would have resulted in a massive disturbance of the marine food chain through the death of much of the plankton. This would have resulted in the eventual death of the marine reptiles which would have relied on the food chain. There would also have been a massive death rate amongst the shelled sea animals like the ammonites. There could also have been a serious increase in the acidity of the seas caused by the acid rains. This may have also killed off some of the sea species.
The period of recovery would have seen the surviving species moving into the ecological niches left vacant by the dead species. After a short period of time some of the plants that had been burnt down would have regrown from buried seeds or rootstock. As is common with all mass extinctions there would have a sudden evolutionary burst as new species developed. The age of the mammals was beginning.
Evidences of a K-T Transition Greenhouse
Eruptions of 90 percent of the Deccan Traps lava pile began at K-T boundary time 65 million years ago (Basu et al., 1993). A carbon cycle perturbation and greenhouse warming began at the same time as the Deccan Traps volcanism and persisted for the duration of the Deccan Traps volcanism. (See Brazos River, Texas, Isotope Record). Other localities showing evidences of K-T transition warming are: Atlantic Ocean DSDP sites 384, 86, 95, 152, 144, 20C, 21, 356, 357, and 329; Indian Ocean DSDP sites 212, 217, 220, 237, and 253; South Atlantic DSDP site 524; Denmark; Biarritz, France; Lattengebirge, Germany; Zumaya, Spain; Caravaca, Spain; and Pacific and Atlantic Ocean DSDP sites.

talk. No one is denying that a large bolide struck. The amount of evidence is convincing and was collected in a great little book by Walt Alvarez called "T Rex and the Crater of Doom" . The title sounds like its some kids book but its a more scholarly attempt to tie the extiction with the "bolide terminator". Remember Walt and his father Louis, were the beginners of the entire K/T boundary bolide story, so Walter has put his career behind the " single bullet theory"

As you mentioned the Deccan Basalts, remember that Pangea was already splitting apart forming the LAurasis and Gondwana segments. These events, in India surround the paran'a-entendeka province from about 130 mya. The flood basalts cluster in a tectonic circle and would have apparently happened whether a meteroite hit or not. Its a geophys coincidence AND the Deccan-Mascarene Ridge province had already developed some flood basalts as a precursor to later events at the close of the Permian and into the Triassic based upon K40 and Pb/Zr ages.

This implied relationship between the events is one that has been a discussion topic for many years since Chixclub wasconfirmed.
The argument for Chixclub as THE terminator event is not very firm except in the areas of western US and Canada. Here the K fossil beds end abruptly at te Iridium layer, whereas in other parts of Gondwana terranes, there is significant time in the sedimentary column between when dinosaurs are disappearing and when the iridium layer appears. We can all agree that the iridium layer is a time-line.
However, in the Gondwana segment, the dinosaurs genera were becoming extint throughout the Cenomanian through the Maastrichtian (90 to 65 mya). This corresponds better with the breakup of Pangea and the occurence of worldwide volcanic shield volcanoes (especially in the Gondwana segments.).
So, while we have a good "story of multiple hypotheses" The entire story for the 30 million year long "mass extinction" has many versions and noone in the game is really 100% behind any one. Evidence keeps getting in the way.

From what I read fossils are a rarity as exceptional conditions are required for fossils to occur. The carcases must be covered before scavengers arrived and must be in a non-acidic environment. The absence of fossils does not mean that there were no dinosaurs around just that the bones were not preserved as they mostly died in forested areas with plenty of scavengers ready to pounce on it and the decaying leaves around thus contributing to an acidic soil condition.

All substances under impact loading act like solids for in stance a plane landing on water at even 60 mph will break up as the water will be like a brick wall. At 100,000 mph impact loading, the earth's crust would behave like a sheet of metal. The asteroid say 13 miles in diameter as part of it burned coming down, would have bent the crust thus the 150- miles crater. That bend in the crust with the volume of a range of mountains, would have added tremendous hydraulic pressure in the mantle which is a viscous semi-liquid. The crust on average is 18 miles thick and only 3 miles thick under the ocean. The asteroid at 12 miles diameter would not have completely broken up or been vaporized by a 18 miles thick crust and as the site of the landing was partially in the Gulf of Mexico where the crust is even thinner. The asteroid would have broken thru the crust. It does not mean the Deccan Traps were created just that they started spewing lava and gas and what not as a result of the seismic pressure waves created by the asteroid.

See below:
The Earth's radius is about 4,000 miles (6,400 kilometers). The main layers of its interior are in descending order: crust, mantle and core.
The crust thickness averages about 18 miles (30 kilometers) under the continents, but is only about 3 miles (5 kilometers) under the oceans. It is light and brittle and can break. In fact it's fractured into more than a dozen major plates and several minor ones. It is where most earthquakes originate.
The mantle is more flexible - it flows instead of fractures. It extends down to about 1,800 miles (2,900 kilometers) below the surface.
The core consists of a solid inner core and a fluid outer core. The fluid contains iron, which, as it moves, generates the Earth's magnetic field. The crust and upper mantle form the lithosphere, which is broken up into several plates that float on top of the hot molten mantle below.
SOURCE: LiveScience reporting

What's your point? Are you suggesting that dinosaurs survived the KT boundary, but didn't leave any fossils (as they did before), and that they eventually died out completely at some later time?

No, just that the iridium layer was the final timeline but fossils do not tell the full story as they are rare events. They are sporadic events. There might have been plenty of dinosaurs around just that their bones were eaten up by the acidic soil.

That is incorrect. When a large meteorite hits a planet or moon the force is too great to be propagated in the same was as a baseball thrown into the sand. It is more like an explosion that happens under the surface. It doesn't matter what angle the meteorite comes in at-- the crater will have a round ejecta pattern. This is also why all of the craters on the moon are circular.

The KT meteorite was about a trillion tons, and the subsurface explosion was the equivalent of 100 gigatons of TNT. In addition to creating a huge tsunami, it put 100 trillion tons of dust into the sky that blotted out the sun.

It also created huge firestorms when the material came down. Since the explision is NOT paraboloid, the ejecta goes out evenly across 360 degrees. The ejecta had enough momentum to go all the way around the globe. Something that is not intuitive at first is that, the opposite pole of the Earth is a singularity which would collect the same amount of falling particles as any ring around the planet...but is much more dense at this pole which is why firestorms happened there, too.