Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: chris on 23/04/2004 09:27:36
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This article, by Helen Pearson, appears in this week's edition of Nature and describes a fascinating theory of dinosaur extinction...
"Dinosaurs may have been forced into extinction partly because there were too few females, say researchers in the UK. The claim revives a venerable debate.
The creatures died out roughly 65 million years ago, around the time that a huge meteor slammed into earth. Some scientists believe that the immense dust cloud thrown up caused swings in the climate that the dinosaurs were unable to survive.
However, it is not clear exactly how the temperature change killed them off. Now David Miller of the University of Leeds and his colleagues are proposing in Fertility and Sterility1 that if dinosaurs used temperature to determine the sex of their offspring, climate changes could have messed up the ratio of males to females.
This idea is based on the reproduction of modern day reptiles such as crocodiles, to which dinosaurs are related. Crocodiles' sex depends on the temperature at which their eggs are incubated. Male crocs hatch in moderate temperatures, while females emerge if the heat rises or falls by a few degrees.
In the case of dinosaurs, Miller suggests that changes in temperature after the meteor impact favoured the birth of males. Over time females would become rare, causing fewer young dinosaurs to be born and species to dwindle to extinction. "They'd probably have had it," he says.
Totally skewed
The idea has been raised before, but few experts were convinced. Palaeontologists currently believe that dinosaurs started dying out around 10 million years before the meteor impact. This was accelerated by a swathe of volcanic explosions and sea level changes that upset the climate, although the details remain unknown.
To strengthen the idea that a sex ratio unbalanced by temperature changes could have been the cause of the dinosaurs' demise, Miller's team built a mathematical model to show how fast a species might become extinct if it deviated from a 50:50 sex ratio, or one male for every female.
If the sex ratio was skewed to 80:20, for example, the model shows that a population of 1000 animals would die out within 50 rounds of reproduction. That might represent only 500-1000 years, depending on the animal's fertile lifespan. "It is an interesting line of argument," says palaeontologist Norman MacLeod of London's Natural History Museum.
But MacLeod says the idea is still a controversial one. The majority of dinosaur experts believe that the animals are most closely related to birds, which do not use temperature to determine sex. Either way, it is hard to confirm: "We do not have Triceratops or Tyrannosaurus rex eggs to incubate," he points out.
Sex change
Miller's analysis also has to explain why some animal groups that use temperature to determine sex survived the change in climate. Crocodiles, for example, lived through the same climate shift.
Miller speculates that they may have been able to protect their eggs from temperature extremes because they lived near cooling streams, or were able to adapt to the changing conditions faster than the long-lived dinosaurs.
He believes that other more robust ways of determining sex might have evolved partly because temperature-dependent sex determination is so risky. Today, most animals including humans use genes to determine sex, so that males inherit one set of sex chromosomes and females another. This ensures a stable sex ratio regardless of meteors or extreme weather.
Some reptiles have clung to the more primitive mechanism. This could be because they live in climates in which their eggs are protected from large swings in temperature, suggests Bruce Lahn, a geneticist at the University of Chicago.
But that leaves these species, which include long-lived turtles, vulnerable to future climate change from global warming. "It is a real concern," says Lahn.
References
Miller, D., Summers, J. & Silber, S. Fertility & Sterility, 81, 954 - 964, doi:10.1016/j.fertnstert.2003.09.051 (2004). |Article|
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Interesting but i'm not convinced... I believe that a combination of factors led to the eventual demise of our reptilian friends. Indeed they began to die out before the Cretacious/Tertiary border (the meteor impact). We know the Meteor event occured through the fossil record which displays both a fine horizon of iridium and shocked quartz and also through spore analysis. It shows a complete turnover of vegetation after the impact with considerable growth of ferns (As they are first to colonise an area after fire etc... These conincide with the impact so plants were directly affected.
I believe that dinosaurs were already struggling due to the extensive volcanism occuring across the Indian Deccan plains which was most probably responsible for the modification of the world climate, they were later hit with the meteoric impact which was a 'nail in the coffin' if you want to call it that. Very few animals survived... and its through this faunal turnover that us mammals have the upper hand today! in fact before the dinosaurs died out, mammals were rather insignificant!
I was also going to raise the point about birds being close relatives of dinosaurs etc... but see that it has been mentioned!
Resident Tour Operator - The Naked Scientists
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Forgot to also add that extensive work has also bee conducted on Planktonic Foraminifera and its extinctions over the Cretacious/Tertiary boundary... it is still not proven whether there was a step-wise or sudden extinction event for forams as cores taken from different areas show differing results. For example a core taken in Tunisia saw an extinction of more than 50 species coinciding with the iridium anomally of the meteor impact BUT a core from Texas showed large numbers of forams to be dying long before the iridium rich layer... You can read more about this work from the paper
Keller.G, Extended period of extinction across the Cretacious/Tertiary boundary in planktonic foraminifera of continental-shelf sections: Implications for impact and volcanism theories; GSA v.101,p. 1408-1419. Nov 1989
I just wanted to point out other sources of evidence supporting a more stepwise extinction through more than one reason.
Resident Tour Operator - The Naked Scientists
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I'm not convinced either. It seems to me that the earth's climate is variable and that the dinosaurs survived way too long to be susceptible to the climate change alone. Current theories are that many if not all of the true dinosaurs were warm blooded. I would think that a warm blooded animal would not use temperature to determine sex of offspring, but I don't know.
Climate change due to massive events such as the Deccan Traps formation, or the asteroid impact, could be enough to cause the extintion just from the loss of habitat and food supply.
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John - The Eternal Pessimist.
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Hi John ( I've missed you matey).....I just wanted to say that I've read all above and find it very interesting indeed. I don't have any postulations of academia of my own to contribute except my appreciation for the interesting topic. Thanks for that.
...still..I suppose the dinosaurs could have just got fed up and evacuated the planet, perhaps they had the benefit of hindsight and decided to let the mammals take over...after all, we've done a real good job eh ?.......
Having said that, is it safe to assume that if the dinosaurs were still around today,. then odds are that it would be one typing this now ? and not some silly ape ?
'Men are the same as women...just inside out !'
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Did anyone ever hear that theory that the dinosaurs all died from constipation?
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What??? This I gotta hear.
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I remember seeing a program about it -- that with the changes is climate, there was a corresponding change in diet that left them all constipated. Now my old people in home health used to swear they felt like dying when they were constipated, so maybe......
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.....surely they still enjoyed a high fibre diet ?...still....if only they knew how to pop to the local drug store/chemist/pharmacist and buy EXLAX or FYBOGEL etc .....it could have been a whole different story eh ?
'Men are the same as women...just inside out !'(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2Flove%2F2015.gif&hash=901cd12278f46c3480e43bc40519e7fb)
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I'm reading a book right now where an alien craft comes to earth to work with our leading paleontologists because their planet had a cataclysmic event in its past similar to the wiping out of our dinosaurs and was on precisely the same timeline. (there's also another species of alien staying on the ship with the ones that landed who also had the same thing happen to them) They are theorizing that it's because of the being we call "God" tinkering with the universe at that point in time. It's a little far fetched but the concepts are cool.
It's called Calculating God, by Robert J Sawyer. I'm not very far into it, but it's good so far.
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quote:
Originally posted by bezoar
I remember seeing a program about it -- that with the changes is climate, there was a corresponding change in diet that left them all constipated. Now my old people in home health used to swear they felt like dying when they were constipated, so maybe......
its interesting to think that any animals that ate that much roughage could get bunged up... a good sunday lunch with plenty of carrots and brussels usually sees me alright! [;)]
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Actually I reckon that the dinosaurs did not die out. it's just that when they saw what a mess us humans were gonna make of the planet they just upped and left in their dinosaur spaceships.... I know this is true cos I just found a departure ticket embedded in some resin for a Mr and Mrs Saurus and Family !!!...and that's the truth !!
'Men are the same as women...just inside out !' (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2FSchilder2%2Finsanes.gif&hash=4f18432872d0188852a6f4a3170ec758)
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quote:
Originally posted by neilep
Actually I reckon that the dinosaurs did not die out. it's just that when they saw what a mess us humans were gonna make of the planet they just upped and left in their dinosaur spaceships.... I know this is true cos I just found a departure ticket embedded in some resin for a Mr and Mrs Saurus and Family !!!...and that's the truth !!
'Men are the same as women...just inside out !' (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2FSchilder2%2Finsanes.gif&hash=4f18432872d0188852a6f4a3170ec758)
lol quality
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is it possible to examine dinosaur egg clutches to determine wheather whole broods were male or female supporting the sterility theory or wheather broods were mixed is there some reason this wouldnt work inability to determine sex or lack of samples?
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Just for the record:
Where did this theory come from ?
I have now written to Nature asking them to explain themselves.
Search Result 1
From: Andrew Kenneth Fletcher (gravitystudy@hotmail.com)
Subject: Re: My simple theory of dinosaur extinction
View: Complete Thread (25 articles)
Original Format
Newsgroups: sci.bio.paleontology
Date: 2000/04/23
Hi Victor
No doubt this played an important part in the extinction of some dinosaur
species.
However, you have ignored the turtle alligators, crocks and lizards.
What if the temperature increased globally by 2 degrees? If you increase the
temperature of alligators and crocodiles eggs by 2 degrees they all turn
into males = end of species.
Could the environmental destruction caused by these massive plant eating
creatures have caused global warming. This would fit with the existence
today of egg laying creatures which lay their eggs close to water.
Overgrazing today is causing global warming. Deserts are expanding and rain
falls in places where it is not needed. Is this a coincidence or is
mankind's greed replicating the same environmental catastrophe.
When a natural barrier such as water is encountered by grazing animals, they
simply move sideward stripping the coastlines and river banks of vegetation.
Thermals rising from the hot dry coastline prevent moisture from travelling
inland resulting in catastrophic reductions in rainfall to inland forest,
which in turn causes forest fires, which in turn add to global warming and
so on. Exactly what is happening today but on a far more worrying scale. It
is said that in the time it takes to smoke a cigarette the Sahara advances
past the smoker.
When the dinosaur became extinct, the environment would have begun to
recover and the deserts would begin to bloom as nature inevitably seizes any
opportunity. When the deserts bloomed and released water again into the
atmosphere, the cooling former-cylinder head of the planet would serve to
reduce global temperatures and the sudden drop in temperature would kick in
and bring about more destruction as you described in your post.
The dingo fence in Australia showed a graphic example of animals meeting a
barrier, albeit manmade. The results to wildlife in Australia are evident
today with the remains of the unfortunate animals scattered for all to see,
along the length of the fence. No vegetation exists on one side, yet the
other side of the fence flourishes.
Man has not eaten the trees, yet has managed to remove most of the forests
from the coastlines around the world. The heat is being turned up by this
imbecilic act of self destruction and is something is not done to halt it
now, we are all doomed to join the dinosaur. Extreme? I think not. It is
generally accepted that the massive buildings of the Egyptians and other
ambitious civilisations, lay in ruins because farming was used to supply the
energy for the massive manpower and animal power required to construct these
magnificent monuments to stupidity.
It is also established and generally accepted that it used to rain more
frequently in Egypt, evident by the weather marks on the sphinx.
An island near India was transformed recently from a thriving mangrove
forest into a desert. Man used the mangrove for fire and the skulls of the
cattle which overexploited the fragile environment serve as a warning to be
heeded by all who are short sighted.
Even in the UK, where it is supposed to rain most of the time, man has
managed to conquer nature. Did you realise that it now rains twice as much
in Jerusalem as it does in the East Anglia region of the United Kingdom. The
massive fields which are used to grow grasses such as wheat and barley are
showing signs of desertification. Massive sand dunes creeping in from the
coastline, too slow for all but a few to notice and too entertaining for
many to realise the significance. Once man removed the trees to increase the
size of the fields it stopped raining. The same happened in the USA when the
great American dustbowl stripped the dry land of fertile soil. The homes of
thousands of people stand today as a monument to the folly of overexploiting
nature. I remember seeing a picture of a man who had to climb up into is
basement. His house stands perilously with all of the exposed foundations
above the level of soil outside.
Andrew K Fletcher
Message Board Title: "INCLINED TO SLEEP INCLINED"
http://www.InsideTheWeb.com/mbs.cgi/mb405491
Victor Grubsky <grubsky@d-startech.com> wrote in message
news:390237D7.8ECF58F0@d-startech.com...
> Hello, everybody,
>
> I just wanted to share my idea why dinosaurs died out. Since I'm not a
> paleontologist/biologist (my background is in physics), my conclusions
> may be wrong, so I'm open to all kinds of critics.
>
> The recent discovery of dinosaur's heart suggests that dinosaurs were
> warm-blooded. So were birds and mammals, who survived the extinction 65
> mln years ago. Why only dinosaurs didn't make it? Let's assume that the
> extinction was caused by a meteorite impact followed by a global drop in
> temperature. The first thing that comes to mind is that all warm-blooded
> creatures would have problems sustaining the body heat. That would
> affect mostly small animals. For big dinosaurs, the ratio of surface to
> body volume (which controls the cooling rate) is very small, so they
> wouldn't have a problem with cold climate. So what sets them apart from
> mammals? The answer is: the way they breed. Dinosaurs laid eggs, mammals
> gave birth to their young. Dinosaur's eggs simply wouldn't hatch in cold
> climate! There was no way for dinosaurs to deal with this problem
> because they couldn't control the temperature of their eggs. In
> contrast, mammals never leave their embryos/young exposed to the cold
> environment. Now what about birds? They lay eggs too, just like
> dinosaurs. But here everything falls in place: we know that birds keep
> their eggs warm using their feathers and body heat! This also explains
> why flying dinosaurs died out and feathered birds didn't. To put it
> simply, the species that took good care of their young survived, and
> those who simply dropped their eggs on the ground paid the price.
>
> Anyway, maybe this idea is not new and maybe it was already rejected as
> nonsense in the past. If so, let me know.
>
> Victor Grubsky
>
>
Death is natures way of telling us to slow down.
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Good thinking, but not all dinosaurs were large and some were feathered. We know that some sat on their nests to keep their eggs warm (Oviraptorosaurs).
Also, by flying dinosaurs do you mean pterosaurs (not dinosaurs) or birds?
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Jurassic Park II
ACT I
Dinosaurs were lords of the Earth for more than 200 millions years. Their supremacy was uncontested...
But 65 millions years ago, dinosaurs suddenly died. They all disappeared in a few years!
Why, only dinosaurs disappeared? when mammals, birds, insects and above all lots of reptiles stay alive!
Why did dinosaurs disappear all at once?
All sorts of explanations have been made to explain dinosaurs' end- epidemic, climate change, competition with mammals volcanic explosion and the meteorite one. And lately some say, dinosaurs were too fat to move quickly to feed and fend themselves...
Personally, I don’t believe any of the above explanations.
ACT II
Humans were lords of the Earth for more than a million years. Their supremacy was uncontested...
But n millions years ago, humans suddenly died. They all disappeared in a few years!
Why, only humans disappeared? when mammals, birds, insects and above all lots of reptiles stay alive!
Why did humans disappear all at once?
Probably, only we would know the answer of the above. The answer would be as follows:
Humans civilization, in its progression, went through stone age, bronze age and iron age. Iron provided teeth and claws to this dinosaur in making. Towards the later part of the iron age, he found a black liquid substance, called crude oil, which proved to be an easy source of energy. There was no looking back for him after that discovery. For all his energy needs there was this answer – OIL. Oil became an integral part of his life. He started growing in size, volume, strength and speed. Using jumbo jets, mammoth ships, giant cranes and huge machines he built sky scrappers, bridges, tunnels, roads etc. He controlled climate using the same easy energy source. He also made lethal weapons and sophisticated nuclear warheads.
Now he could not think of a life without this natural resource. The ease of using this resource, resulted in its wasteful use in copious quantities. Soon, this substance became scares and came at the verge of exhaustion in the womb of mother earth.
…And this was the time, man took arms against man. There were fight for possession of oil fields. Man became man’s enemy. Third world war resulted. Nuclear warheads were used. Most of their population was wasted in this war for oil. Few remained after the war, but due to exposure to nuclear radiation these men were not able to reproduce and it was matter of time that dinosaur II, disappeared from the face of this earth…
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Now, I think I have an answer for dinosaur-I’s extinction.
I guess, in their last days, they got used to some natural resource, which slowly exhausted from the earth, as oil in our case. And there was a big fight among these dinosaurs for its possession. Weaker dinosaurs were eliminated. And among the stronger dinosaurs, the weaker sex. The earth was left with similar sex dinosaurs, which could not reproduce and hence became extinct.
b rgds
sudhir
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Hmmmm Alrighty then :)
In the red orner we have dinosaurs, and in the blue corner the aligators and crocks perhaps? And a possible tag team of teenage ninja turtles and tortise.
But certainly made me smile :)
quote:
Originally posted by sudkjain
Jurassic Park II
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Now, I think I have an answer for dinosaur-I’s extinction.
I guess, in their last days, they got used to some natural resource, which slowly exhausted from the earth, as oil in our case. And there was a big fight among these dinosaurs for its possession. Weaker dinosaurs were eliminated. And among the stronger dinosaurs, the weaker sex. The earth was left with similar sex dinosaurs, which could not reproduce and hence became extinct.
b rgds
sudhir
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it was mainly due to the fact of asteriods and a scarce amount of food