From the AGU:
Global fires after the asteroid impact probably caused the K-Pg extinction
About 66 million years ago a mountain-sized asteroid hit what is now the Yucatan in Mexico at exactly the time of the Cretaceous-Paleogene (K-Pg) mass extinction. Evidence for the asteroid impact comes from sediments in the K-Pg boundary layer, but the details of the event, including what precisely caused the mass extinction, are still being debated.
Some scientists have hypothesized that since the ejecta from the impact would have heated up dramatically as it reentered the Earth’s atmosphere, the resulting infrared radiation from the upper atmosphere would have ignited fires around the globe and killed everything except those animals and plants that were sheltered underground or underwater.
Other scientists have challenged the global fire hypothesis on the basis of several lines of evidence, including absence of charcoal-which would be a sign of widespread fires-in the K-Pg boundary sediments. They also suggested that the soot observed in the debris layer actually originated from the impact site itself, not from widespread fires caused by reentering ejecta.
Robertson et al. show that the apparent lack of charcoal in the K-Pg boundary layer resulted from changes in sedimentation rates: When the charcoal data are corrected for the known changes in sedimentation rates, they exhibit an excess of charcoal, not a deficiency. They also show that the mass of soot that could have been released from the impact site itself is far too small to account for the observed soot in the K-Pg layer. In addition, they argue that since the physical models show that the radiant energy reaching the ground from the reentering ejecta would be sufficient to ignite tinder, it would thereby spark widespread fires. The authors also review other evidence for and against the firestorm hypothesis and conclude that all of the data can be explained in ways that are consistent with widespread fires.
Source:
Journal of Geophysical Research-Planets, doi:10.1002/jgrg.20018, 2013
http://onlinelibrary.wiley.com/doi/10.1002/jgrg.20018/abstract
Title:
K/Pg extinction: Reevaluation of the heat/fire hypothesis
Authors:
Douglas S. Robertson: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA; William M. Lewis: Department of Ecology and Evolutionary Biology and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA; Peter M. Sheehan: Department of Geology, Milwaukee Public Museum, Milwaukee, Wisconsin, USA; Owen B. Toon: Department of Atmospheric and Oceanic Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA.
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PS: Hesperornis kin didn’t survive while wholly beaked divers might have not because the former had teeth, but more probably because of their lack of mobility on land & dependence on habitats severely hit by the effects of the Yucatan impact.
“””””……tty says:
March 28, 2013 at 4:41 am
“So the orbital period at earth surface is 84 minutes. So how does that “ejecta” re-entry shower last “several hours” ?
Enquiring minds want to know.”
Because most of the re-entering ejecta was ejected at high angles into very excentric elliptic trajectories which only re-enters the Earths atmosphere several hours later. As a matter of fact a fair amount probably went into orbits around the Sun. I would expect that there was a lot of shooting stars for centuries afterwards as the Earth swept up most of the debris……”””””
Well I understand how ballistic trajectories work. An ejected particle, will never have more energy, than at the instant it is blasted from the ground, and at the time of highest kinetic energy, it also is in the densest atmosphere, and therefore losing energy due to radiation and the friction that heats it.
It will exit earth’s atmosphere (if high trajectory) with much lower energy than it had on launch, and it will arrive back at earth upper atmosphere at no more than that energy.
So any intense infrared radiation is going to be concentrated in the first few seconds of the ejection phase, since the maximum amount of ejected material with the highest energy, is present at that time.Simple randomness, will spread the objects into a broad spectrum of orbits, so the returning material (only part of it returns) arrives spread out in time, and reduced in energy from what launched from the ground.
I see no way, the returning material can create as much thermal havoc as the ejected material made in just a few seconds. And as for some material going into sun orbit; where else could it possibly go.
And I would doubt that much of that material is ever encountered again by earth on later trips around the sun.
And returning material will be in the atmosphere for a few seconds at most. I simply don’t buy a rain of infrared cooking for hours.
PPS: I went to the Oceans of Kansas site (not Seas; I shouldn’t rely on memory at my age) to learn more myself about mosasaurs & found this info relevant to their salinity & depth preferences:
“Mosasaurs ruled the oceans of the Late Cretaceous and were beginning to invade fresh water environments such as estuaries, swamps and rivers when the Age of Dinosaurs ended.”
Not a member of the snake-lizard clade I’d want swimming up any river near me. Thank God for the bolide impact. Creative destruction for mammals.
“””””…..Doug Jones says:
March 28, 2013 at 12:19 am
george e. smith, the ejecta from a major impact comes out at a wide ranges of velocities, from slow to fast, from low to high angles but mostly around 45 degrees…..”””””
So what is the mechanism that focusses the ejecta into trajectories around 45 degrees. Certainly the longest ranging paths, at any launch velocity, would ocur around 45 dgree launch angle. But what causes more objects to choose that launch angle ? How is that process modulated by the original object impact angle ?
“When the charcoal data are corrected for the known changes in sedimentation rates, they exhibit an excess of charcoal, not a deficiency.”
There’s not enough charcoal in the sample, so rejigger the sedimentation rate data and tada! there’s excess charcoal in the sample. Nevermind the amounts of charcoal or anything else in the sample hasn’t actually changed.
To quote Adam Savage “I reject your reality and substitute my own!”
If X amount of sediment containing C amount of charcoal was deposited in T amount of time, that’s how much charcoal there is. “Correcting” the sedimentation rate to what’s observed from some other sample is simply bad science, heck that’s not science at all. One can *compare* data from different samples to get a *contrast* between them, but one cannot take some measurement from one sample, apply it to another sample and claim “The data supports my theory.”.
It’s the same sort of “science” as claiming that two monitoring sites in Australia, at two different altitudes and different distances from the coast, are measuring the same temperature because one came after the other in time and was assigned the same designation when the preceding one was decommissioned.
Even without assuming IR radiation-ignited global fires, with consequent increased atmospheric CO2, other effects of the impact(s) can account for observed extinctions.
Among these are: 1) megatsunamis, 2) inhibition of photosynthesis from lofted dust & sulfuric acid aerosols (the bolide struck gypsum deposits, producing SO2, precursor of sulfuric acid) & 3) acid rain (but not enough to kill off all amphibians).
http://www.sciencemag.org/content/327/5970/1214
The lower level of O2 detected in the early Paleocene does however suggest at least regional firestorms.
The climate was changing at the end of the Cretaceous, as it always does. The oceans were regressing, perhaps due to less undersea volcanism. The Deccan Traps were spreading over the Indian Plate due to surface volcanism.
But the climate was still in Hothouse mode, where it remained until global cooling set in from the mid-Eocene, ~49 Ma (attributed by some at least in part to the Arctic Azolla Event). IMO it’s therefore likely that dinosaurs & other archosaurs would have continued to dominate the land & other diapsid reptiles the seas for at least another 16 million years absent the Yucatan impact. Indeed, mammals still didn’t become dominant until well into the Cenozoic Era, with birds & snakes ruling many terrestrial & marine environments in the Paleogene Period. For that matter, terror birds (They eat horses, don’t they?) ruled the roost in South America even in the Neogene, until the Isthmus of Panama connected that then-island continent with North America in the Pliocene Epoch. Indeed birds dominated New Zealand & some other oceanic islands until the Holocene arrival of humans, & giant varanid lizards (goannas) remained among the top predators of Australia.
Staten-John says:
March 28, 2013 at 10:10 am
@TomR,Worc,MA
The sea-going reptiles, not dinosaurs, were wiped out at the K-T interval because an increase in surface gravity
Dear John, before any discussion about an increase in gravity, please try to run the numbers and check what variations in gravity would be achieved through continental drifts.
The theory that was posted by you above does not show any numbers, it just states that a variation change occurred. But the variations that the theory talks about are minimal, as the continental crust is only tens of kilometers in comparison with 6000+ kilometers of the Earth radius.
Please try to use Newtons law and look at the numbers that you get. A very high level approximation should be enough to give an idea.
https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation
Of course even now we can see gravitational differences between areas, for instance as undersea volcanoes achieve to raise the sea level above them by a couple of meters through their mass.
Even greater differences are between the equator and the poles, as the earth is rotating and this creates a difference which is much above what one can achieve with continental drift:
https://en.wikipedia.org/wiki/Gravity_of_Earth
“In combination, the equatorial bulge and the effects of the Earth’s inertia mean that sea-level gravitational acceleration increases from about 9.780 m·s−2 at the Equator to about 9.832 m·s−2 at the poles, so an object will weigh about 0.5% more at the poles than at the Equator.[3][4]”
But no extinction is happening because of this for any birds flying from the cold to warmer areas or humans travelling…
@LarsP
Don’t be offended by my response because most people don’t understand the Law of Conservation of Angular Momentum (LCAM). An explanation can be found on Wikipedia.
As I have explained in many forums, the change in surface gravity is the result of Pangea’s center of mass moving well north and south of the equator. If you reads the link to the summary I posted previously, you will find scientific verification of this movement.
If you understand LCAM, you would know that Pangea’s north or south movement would alter the Earth’s AM unless one of two things happened:
1. The Earth’s rotational speed changed
OR
2. The core elements moved to away from centricity.
The first option did not happen, leaving the second option.
The mass of Pangea is small compared to that of the Earth, however it is not this mass alone that is significant. It is the mass times the distance of the mass from the rotational axis SQUARED, that is significant. This number is very large. Review moment of inertia also.
@John Tillman
“The paper linked below suggests that neornithine birds may have survived the extinction thanks to their ability to dive, swim or shelter in aquatic & marshy habitats.”
If this were a viable explanation then some seagoing reptiles would have survived, yet not a single one of the them, large or small, survived.
My belief, since no one seems to have a logical explanation, is that the neornithine birds were better suited to survive increasing surface gravity which occurred over tens of thousands of years.
Perhaps the archaic birds that became extinct were primarily gliders, not capable of full powered flight.
This recent paper shows that mosasaurs invaded freshwater environments remarkably early in their history. From what I read at Oceans of Kansas, I got the idea that perhaps this happened only in the Maastrichtian Age (end Cretaceous, 72.1-65.5 Ma), but they’ve been found in a Hungarian freshwater site from way back in the Santonian (85.3–83.5 Ma):
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051781
During the Maastrichtian, a pronounced marine regression occurred, so that the northern half of the Western Interior Seaway on North America dried out & the remaining southern portion narrowed, making abundant coastal plain habitat for such familiar & strange dinosaur characters as, among theropods, carnivore T. rex, possibly omnivorous Troodon & Ornithomimus, giant herbivore Therizinosaurus, birds, including the maritime Hesperornis; the enormous sauropod Alamosaurus; plant-eating ornithischians Triceratops, Ankylosaurus, Pachycephalosaurus & a variety of hadrosaurs. So I thought maybe the receding seas accounted for mosasaurs invading fresh & brackish waters, but apparently these aquatic environments had been attracting them for over ten million years by the Maastrichtian. Clearly, at least some of them liked shoals.
Why not stop making easily disproved, uneducated assertions & actually do some research & thinking before typing. The archaic birds were most certainly capable of powered flight. They had asymmetric flight feathers, keeled sterna (meaning breast meat due to big flight muscles) & pygostyles (“parson’s noses”) sprouting tail feathers for precise control of aerial maneu, just like modern birds. Opposite birds were such good fliers that they out-competed all the smaller pterosaurs, which had gone extinct before the impact, leaving only a few gigantic flying reptiles to be wiped out by it. Until you got close enough to see their tiny teeth & claws, they would have looked like modern birds. Hoatzins still have claws.
I’ve already pointed out to you that not all marine reptiles went extinct. Your lame, made-up excuse that mosasaurs & plesiosaurs must have inhabited deeper water than sea snakes & sea turtles has already been shown false. As I’ve indicated, mosasaurs even invaded rivers, swamps & estuaries, so some lived in waters no deeper than crocodilians, of which there were in any case marine species in the Cretaceous. The marine habitats of plesiosaurs & mosasaurs were primarily shallow epeiric seas or the continental shelves of oceans.
Giant sea snakes replaced their mosasaur kin as marine predators in the Paleocene Epoch.
By the K/T boundary 65.5 Ma, archaic birds had been adept powered fliers for more time than has passed since the extinction then. As long as 80 million years is possible, ie since the Jurassic/Cretaceous boundary:
http://en.wikipedia.org/wiki/Pygostylia
Even Archeopteryx, from the Late Jurassic some 90 million years before the K/T, was able to fly, although it lacked a keeled sternum & had a long tail like most theropods instead of a pygostyle. Paleontologists are coming to regard Archie as a flying dromeosaurid (Velociraptor kin) rather than a “bird”. There were other flying maniraptoran dinosaurs in the Early Cretaceous, trying out different systems, like the four-winged Microraptor. So by the K/T, opposite & modern birds & those in between had millions of years of strongly powered flight behind them.
Staten-John says:
March 29, 2013 at 12:18 pm
@LarsP
Don’t be offended by my response because most people don’t understand the Law of Conservation of Angular Momentum (LCAM). An explanation can be found on Wikipedia.
…..
The mass of Pangea is small compared to that of the Earth, however it is not this mass alone that is significant. It is the mass times the distance of the mass from the rotational axis SQUARED, that is significant. This number is very large. Review moment of inertia also.
I am not offended. I have been called denier and worst, I do not get easily offended, I learned that mostly people do project their own misunderstandings on others.
So please John, try to do the math and run the numbers. There is no use to continue the discussion without showing a calculation.
@John Tillman,
“The archaic birds were most certainly capable of powered flight.”
Where is your proof of this statement? You’re only giving your opinion. Also, the presence of claws indicates that they most likely did a lot of tree climbing, not something a bird capable of ordinary flight would have, but gliders would have.
All seagoing reptiles went extinct, contradicting what you wrote.
The Western seaway was gone before the asteroid impact due to the massive regression, therefore, your comments about the mosasaurs occupying shallow waters at the K-T transition is unfounded. Also, you don’t know if the mosasaurs that entered shallower waters had to return to deeper waters to reproduce. Again, a lot of this is just your opinion.
Staten-John:
I gave provided convincing evidence that archaic birds were excellent fliers. No use replying to you if you ignore all I say & refuse to read links I provide or do any actual research on your own. Not to mention flat out lying about what I said re. sea-going reptiles.
Archaic birds, just like modern birds, had brains adapted for flight control, asymmetric flight feathers, a keeled breastbone with large muscles for wing flapping & tail vertebrae fused into a pygostyle to which was attached tail feathers to provide more lift & to make the same kind of fine control movements as in modern birds. These are observable facts, not my opinion.
Again, opposite birds’ flight capabilities were so good that they drove all but the largest pterosaurs to extinction. How many times do I need to repeat the same facts?
Hoatzin chicks have two claws, which they use when threatened by predators to crawl out of their nests before they can fly, as their parents try to divert the attackers. The chicks also can drop into swamp water, then climb back up to the nest. Most if not all modern birds lose their claws in adulthood, but most if not all opposite birds retained them, just as most but not all had teeth. It doesn’t mean that opposite birds were worse fliers than hoatzins. Had you ever studied evolution, these facts & inescapable conclusions would not surprise you.
Modern birds survived not because they were better fliers but due to other abilities & behaviors, plus where they lived. Again, I’ve repeatedly presented evidence to this effect. Here’s a new one, ie better sense of smell:
http://www.livescience.com/13682-birds-survived-mass-extinction-dinosaurs.html
As for marine reptiles, why do you keep ignoring sea snakes, turtles & crocs? Of course the Interior Seaway had retreated, but that created shallow habitat elsewhere. It still existed over the US, but had receded from Canada by the K/T. Mosasaurs & plesiosaurs had global distribution, but everywhere avoided ocean depths. Their prey lived near the surface.
These two groups of marine reptiles died out not because they had to swim from lower depths but because their main food sources, belemnites (plesiosaurs) & ammonites (mosasaurs), went extinct due to the effects of the impact on ocean chemistry & primary production. For larger mosasaurs, it was their plesiosaur prey that failed, following loss of belemnites. Many if not all plesiosaurs were bottom feeders, gliding over continental shelf shoals looking for food.
Both mosasaurs & plesiosaurs gave live birth, which would necessarily have been in shoals, so that their young could breathe. Please quit trying to make up excuses, but rather study & think.
There is zero evidence in support of your idea & all the fact & reasoning in the world against it. Sorry.
PS: As noted before, modern birds’ new nesting strategies, which obviated the benefit of chicks growing claws, is one reason scientists have assessed for their survival of the impact. Like many birds today, Cretaceous neornithes nested in hides on marshy ground, on cliff faces, in cavities in trees & in burrows, not just on tree branches.
Many, like ratites, had already lost the ability to fly. Same applies to partially toothed relatives of neornithes, like Hesperornis. Young ratites still retain vestigial wing claws today, as do some flying species besides hoatzins, like turacos & yellow rails. Note that all these are Gondwanan birds, except the yellow rail, which oddly is a marsh dweller. But that’s evolution for you.
@John Tillman
Let’s be honest about it, neither one of us will be able to prove that archaic birds had the same flight ability as the neornithes. The few bones and feather imprints are not sufficient evidence to establish this. We are both giving our personal opinion.
I read your link and find the sense of smell explanation incredulous. If the airborne debris from the impact played a role in the extinctions, birds with the more sensitive sense of smell would have been more vulnerable.
You are basing your analysis on the assumption that the impact was the cause of the extinctions. In other words, you believe in an instantaneous (geologically speaking) extinction.
I believe that surface gravity was gradually increasing during the late Cretaceous with a rapid pulse near the end. The theory posted requires the rapid pulse of surface gravitation when a large rapid marine regression occurs. A large eruption of flood basalt volcanism must also occur (usually lagging the extinctions). If you study all the mass extinctions, these two scenarios are common to all mass extinctions.
Hopefully, in the near future, the scientific community will finally agree on the definitive cause(s) of the K-T extinctions.
@LarsP
“So please John, try to do the math and run the numbers. There is no use to continue the discussion without showing a calculation.”
What math would you like to see? Be specific.
Staten-John says:
March 30, 2013 at 9:34 am
What math would you like to see? Be specific.
What variations in gravity are you talking about.
I already asked in the very first post specifically this:
March 29, 2013 at 10:36 am
…before any discussion about an increase in gravity, please try to run the numbers and check what variations in gravity would be achieved…
The scientific community has already agreed on the cause. I posted the link here. It’s not consensus science but the overwhelming preponderance of the evidence. Skeptics have had decades to destroy the impact theory without making a dent.
Had you read any of the links I’ve posted you’d know that there was a great diversity of avian life at the end Cretaceous. It doesn’t matter if you imagine, contrary to all evidence, that opposite birds couldn’t fly as well as more “modern” groups. As I said in my first comment on this topic, many modern & modernish birds went extinct at the K/T along with the most “primitive” opposite birds.
For instance, the common shore bird Ichthyornis was “modern” in all respects except teeth. Its wings lacked claws. Same goes for the related diving bird genus (flightless like penguins & great auks) Hesperornis. They belonged to the group Ornithurae, sister taxon to Enantiornithes, the opposite birds. The Ornithurae include both “archaic” forms like the sea & shore bird genera mentioned & the Neornithes. Here’s a chart from one of my posted links showing these relationships for a community at the K/T boundary in western North America:
http://www.pnas.org/content/108/37/15253/F4.large.jpg
But then opposite birds were in fact good fliers. If you suppose not, then please explain what purpose you imagine for the anatomical details I pointed out. The burden of proof is on you to show that they couldn’t fly well, since all informed thought on the subject concludes that they could.
In any case, it wasn’t their flying ability that doomed the opposite birds. The basal & derived Ornithurae, most of which (except some modern groups & possibly one non-neornithes, as noted previously) went extinct along with the Enantiornithes, had the shoulder joint configuration of modern birds (which facilitates the up stroke), so there goes that lame excuse of yours. Not all their fossils show the birds’ hands, so we don’t know if most Cretaceous ornithurae lacked claws like moderns, but probably so, since the most basal forms, like Ichthyornis did. We often lack their skulls, too, so don’t know how common teeth might have been among the non-neornithes ornithurae.
I wouldn’t have to waste time providing you with all this info had you bothered to read the links I’ve posted. And if you were willing to think.
Staten-John says: I believe that surface gravity was gradually increasing during the late Cretaceous with a rapid pulse near the end. The theory posted requires the rapid pulse of surface gravitation when a large rapid marine regression occurs. A large eruption of flood basalt volcanism must also occur (usually lagging the extinctions). If you study all the mass extinctions, these two scenarios are common to all mass extinctions.
*******************************************************************************************
Forgot to respond to this blatant falsehood.
You clearly have not studied all mass extinction events. Your two scenarios most certainly are not common to all of them. Contrary to your assertion, the O/S extinction occurred when volcanism ceased. The marine regression at that time followed glaciation. It had nothing to do with gravity pulses. The prior Cambrian extinctions are also associated with glaciation. The following Devonian extinction coincided with marine transgression, not regression.
Have you considered actually studying the science to which you wish to contribute?
If you want to overturn a scientific paradigm, then do as real scientists have done in the past & spend decades assembling data & couching argument, as did Copernicus & Darwin. Then show how your hypothesis better explains observed reality than the prevailing consensus, in detail. For starters, how about showing the superiority of your explanation for the disappearance of belemnites & ammonites, followed by their predators mosasaurs & plesiosaurs, over those based upon the K/T impact?
Then show in the case of every other group which went extinct at the K/T how the impact theory fails & your alternative scheme succeeds. Also of course provide evidence that terrestrial gravity actually behaved as you suppose, & that it could have produced the observed extinctions.
You haven’t & can’t so you’re falsified before you even begin. Idle speculation doesn’t cut it, sorry.
PS: If all MEEs have the same cause, then explain please why trilobites survived the Cambrian, Ordovician & Devonian extinctions finally to succumb only in the Permian, Mother of All MEEs. Similarly, why did ammonites survive the Devonian, Permian & Triassic events but not the Cretaceous?
Also, why did shallow water-dwelling ammonites & belemnites perish at the K/T, while deep-living nautiluses came through, if gravity be the cause of the MEE?
The K/T impact has the distinct advantage of actually having happened at the precise moment in geohistory that all those lifeforms went extinct. OTOH, there is zero evidence for the gravity pulses you imagine. Zip, nada, bupkus.
@John Tillman,
“Archaic birds, just like modern birds, had brains adapted for flight control.”
This statement, like all of your statements are just your opinion, nothing more. There is just no way you can prove that statement.
No, the smaller pterosaurs were driven to extinction because an increasing surface gravity mandated that they increase their wing area to body mass ratio. The only way they could do that was to also increase their body size.
You now start to use extant birds (i.e., Hoatzin chicks) to birds over 65 million years old regarding claw usage. I cannot spend time pointing out all of your illogical comparisons.
If you really want to have some credibility explain why Enantiornithine B went extinct before Enantiornithine A. Obviously the impact was not responsible.
As far as the ammonites going extinct but not the nautilus, you will find a detailed explanation in the book with the same name as the theory. They were quite different structurally and the ammonite changed substantially between the P-T extinction and the K-T extinction while the nautilus did not.
If you studied the mass extinctions you mention you would know that the glaciation involved was insufficient to cause the associated regressions. And you might want to try to explain why the sea level at the end of the Permian (i.e., no glaciation) was lower than it is today (i.e., with glaciation).
http://en.wikipedia.org/wiki/File:Phanerozoic_Sea_Level.png
“Have you considered actually studying the science to which you wish to contribute?”
I would ask you the same question.
@LarsP
“What variations in gravity are you talking about.
I already asked in the very first post specifically this:
March 29, 2013 at 10:36 am
…before any discussion about an increase in gravity, please try to run the numbers and check what variations in gravity would be achieved…”
If you are asking what percentage drop in surface gravity occurred I would guess at least 50% based on the size of the largest fauna. It could be more.
This is the number used in the book with the same name as the theory we are discussing. The mass of the shifted core elements (inner core, outer core and densest part of lower mantle) which represents about 85% of the total mass of the Earth had to move away from Earth centricity to cause the lower surface gravity on Pangea.
You provided Newton’s equation for the force of gravity in an earlier post. I assume you can solve this simple equation. Use that equation to calculated the shift needed for a 50% reduction in the force of gravity on Pangea. Give the answer in a fraction of the Earth’s diameter needed for the shift.
Staten-John says:
March 30, 2013 at 6:19 pm
A load of garbage…
http://en.wikipedia.org/wiki/File:Phanerozoic_Sea_Level.png
***************************************************
So much ludicrously, ridiculously wrong; so little time.
How many times do I need to show you from actual anatomy that the traits of opposite birds & their early modern kin are not matters of opinion but fact? Do you know the difference?
The brains of the earliest opposite birds were intermediate between that of Archaeopteryx & modern birds. Adaptations for powered flight are plain in the brains of birds, as of pterosaurs. It’s also possible to infer whether they fed by day or night, whether they were precocial & much else about their lives & behavior. Forming opinions on these topics has to be based upon observation, which sometimes leads only to one conclusion.
How exactly is it “illogical” to infer behavior of extinct birds from that of modern birds? Scientists often use modern analogies to reconstruct past behavior from living relatives & even not closely related ecological analogues. Had you ever studied any of the relevant disciplines, you’d know this. It has been repeatedly shown a valid technique.
It’s obvious you still haven’t read the paper from which I linked the chart, although I posted it early in this thread. Both Enantiornithines A & B are from the same horizon at the K/T boundary. They went extinct at the same time. The slight displacement of B relative to all the other ultimate dots is a tiny typo, as would be obvious had you bothered to educate yourself, which you’re clearly either afraid or too lazy to do.
The fact remains that your ignorant assertion that birds did not go extinct at the K/T has been falsified every which way. The vast majority of birds went extinct along with their dinosaur kin. This includes lots of modern birds & semi-modern birds like members of the Ichthyornis & Hesperornis families. Opposite birds were already on their way out by 66 Ma.
You commit the logical fallacy of begging the question (assuming what you intend to prove) by asserting without the slightest actual evidence that pterosaurs were going extinct due to gravity changes.
You failed to explain why belemnites & ammonites didn’t go extinct during prior MEEs, which you suppose all occur because of imaginary “gravity pulses”. Ammonites survived the devastating P/T, along with the prior D/C & later Tr/J MEEs. They constantly evolved, both in shell form but also physiology & reproduction from their straight-shelled Silurian ancestors. Their rapid evolution is what makes them such good stratigraphic markers.
Ammonites were in decline in the LK, although as usual evolving new shapes. The order was reduced to a few families but their final disappearance was too sudden (along with belemnites) to be explained by background natural extinction. The impact affects would thuns have hit them harder than nautiloids because ammonite larva were planktonic, high in the water column. Nautiloid eggs are large & stay deeper.
Also, ammonite shells were composed of aragonite (mother of pearl), which would have been highly susceptible to acid rain from the vaporizing & lofting enormous beds of limestone into the atmosphere by the impact. The deeper-water nautilus was more protected. Maybe ammonites lost out to other competitors for the scarce resources left after the bolide hit.
Nautiluses have changed less because they continued to inhabit more stable, benthic environments.
To which glaciation do you refer in not being able to account for the marine regression? I cited the O/S. Please present some evidence to support this unfounded assertion. Paleontologists & geologists who have actually studied the Ordovician glaciation adamantly disagree with you:
http://www.ucmp.berkeley.edu/ordovician/ordovician.php
“During the Upper Ordovician, a major glaciation centered in Africa occurred resulting in a severe drop in sea level which drained nearly all craton platforms. This glaciation contributed to ecological disruption and mass extinctions…Climatic fluctuations were extreme as glaciation continued and became more extensive. Cold climates with floating marine ice developed as the maximum glaciation was reached.”
You are aware are you not that Pangaea was long gone by the K/T boundary? It started splitting up in the Late Triassic, about 200 Ma. By the Late Cretaceous, 66 Ma, Earth more resembled now than the Early Triassic, with isolated continents. Parts of Gondwanaland were still connected, but Africa & South America had separated, as had all the parts of Laurasia.
Now we come to the most hilarious part. The chart you show of reconstructed sea level neatly makes my point, not yours. Both its curves plainly show marine transgression at the Devonian MEE, as I told you, not regression as you so falsely claimed for “all” extinctions. You have not ever studied MEEs before. I have. All you imagine you “know” comes from a readily falsified book without a shred of supporting evidence for its underlying speculation.
Please don’t comment again until you have taken the time to study, learn & think.