Hmm, you may be on to something:
Posted on 04/21/2004 11:45:26 AM PDT by Junior
WASHINGTON (Reuters) - An asteroid may have wiped out the dinosaurs 65 million years ago not simply by changing the world's climate and causing years of dark skies, but also by causing too many of them to be born male, U.S. and British researchers say.
If dinosaurs were like modern-day reptiles such as crocodiles, they change sex based on temperature, David Miller of the University of Leeds in Britain and colleagues noted Tuesday. And even a small skewing of populations toward males would have led to eventual extinction.
Most experts agree that one or more asteroid impacts probably triggered a series of global changes that killed off the dinosaurs and many other species of life on Earth. The impacts would have kicked up dust that cooled the air and also triggered volcanic activity that would have created even more dust and ash.
No one really knows if dinosaurs were more like reptiles, or something closer to mammals. Reptiles have very different metabolisms than mammals and also have various ways of determining the sex of offspring.
In mammals, if a baby gets an X and a Y chromosome, it will be male and if it gets two X chromosomes it will be female, with a few very rare exceptions. Similar mechanisms work for birds, snakes and some reptiles such as lizards.
But in crocodilians, turtles and some fish, the temperature at which eggs are incubated can affect the sex of the developing babies.
Miller's team ran an analysis that showed a temperature shift could theoretically have led to a preponderance of males. Other studies have shown that when there are too few females, eventually the population dies out.
"The earth did not become so toxic that life died out 65 million years ago; the temperature just changed, and these great beasts had not evolved a genetic mechanism (like our Y chromosome) to cope with that," said Dr. Sherman Silber, an infertility expert in St. Louis who worked on the study.
But crocodiles and turtles had already evolved at the time of the great extinction 65 million years ago. How did they survive?
"These animals live at the intersection of aquatic and terrestrial environments, in estuarine waters and river beds, which might have afforded some protection against the more extreme effects of environmental change, hence giving them more time to adapt," the researchers wrote.
"Like" modern birds does not mean "identical to" modern birds. Under the right conditions even a small difference can be a critical one.
2. Large reptiles, like crocodiles, survived.
Read the article, they covered that.
I think that I remember seeing a program where a major paleontologist commented on the declining diversity amoung dinosaur species BEFORE the asteriod impact event 65 million years ago. I guess that science writers can't get past their disaster-theory -- Just easier to sell to us poor, dumb, ignorant masses
Or maybe the "dumb, ignorant masses" aren't aware that several different factors can all contribute to an extinction, it's not a matter of "one cause which excludes all else". Few extinctions are due to *one* single thing acting alone -- they're usually due to a combination of things which together stack the odds sufficiently against the species to do it in.
If dinosaurs were already declining due to some other factor (e.g. climate change, competition from mammals, etc.), then they'd be more vulnerable to a major event like a large asteroid strike. Either one alone probably wouldn't have wiped them out. For example, perhaps without a prior climate-driven decline, an asteroid strike wouldn't have been able to knock off *all* the dinosaurs and a few hardier species would have survived to present day along with the crocodilians, etc.
I did a quick web search. The ichthyosaurs were already extinct well before the end of the Cretacious:
Ichthyosaurs swam in the Mesozoic ocean when dinosaurs walked on land. To be precise, they appeared slightly earlier than dinosaurs (250 million years ago versus 230 ma) and disappeared again earlier (90 ma versus 65 ma).
They, and the plesiosaurs, were aquatic reptiles, not dinosaurs (there is a bit of a difference). The plesiosaurs evidently lasted right up to the end of the Cretacious. It is possible that a general collapse of the aquatic ecology caused by the die-off of algae and the itty-bitty critters that lived on it and cascading up the food chain, would have killed off these top-niche predators. Sharks survived, but they weren't necessarily large animals. The megaladon comes much later in the fossil record.
Hmm, you may be on to something:
Genetic trivia: In mammals (including humans, of course) the XX form is female and the "mixed" XY form is male. But in birds it's "backwards" -- the male birds have the matched "AA" sex-determining genes and the females have the mixed "AB".
I love that movie, but they shouldn't have left the impression that dodos went extinct during the ice age. Instead they went extinct rather recently, in the mid 1600's.
Soccer causes extinction.
"You, Rex...Breeding Red Card!"
Movie trivia: In that scene, when Manny and friends ask for one of the watermelons, the dodos say:
Dodo: "If you weren't smart enough to plan ahead, then doom on you!""Doom on you" may seem like a stilted phrase, but that's because it's an inside joke. The English phrase "doom on you" is phonetically almost identical with the Vietnamese phrase "Du-ma-nhieu", which means roughly "go f*** yourself".
Other Dodos: [chanting] "Doom on you! Doom on you! Doom on you!"
Some English-speaking folks who are acquainted with Vietnamese cursing (like VN war vets, for example) sometimes use "doom on you" as a joking form of the original phrase, just as WWII vets sometimes used "mercy buckets" for "thank you" in parody of the French "merci beaucoup".
Check out the above link. Some survived until the end of the Cretacious.
Mike
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