dinos

[piterdevries]

just finished michael crichton's jurrasic park and lost world novels.. there are hell many theories on how the dinos died out.. for you,wat is the real theory? for me the meteor impact at yucatan peninsula.

[Andrew]

Sounds interesting. This thread lead me to finding Google earth placemarks for craters and such. Good stuff, includes an overlay for the yucatan peninsula. There are lots of craters.

Surprised we havn't seen any impacts in human history.

I'd have to say meteor impact sounds convincing.

[Dante]

Meteor impact, probably combined with an already present upheaval in the Earth's crust.

[Procyon]

  an already present upheaval in the Earth's crust.

You know that my english is not my mother language. What means "upheaval"?

The theory about the meteor is the most known. In the mayan and azteca cultures were some sacred craters, full of water, called cenotes; product of that meteor.

Another theory is that some of the primitive mammals of the cretacic consumed the eggs of the Dinosaurs, but then why there are birds and reptiles?. The DS eggs were probably something similar to them, and some with the same size.

A more phyosophical-physic theory is the gigantismus of the creatures of mesozoic was caused by the gravitation of the moon, which in that time (245 to 65 million years ago), the moon was closer than today.

The posterior movement away from the earth, caused the disminution of the moon gravitational force in the Earth ( F=(G*m1*m2)/d^2 ) causing an apparent "augmentation" of the Earth's gravitational force, causing collapse in the DSs esqueleton. I think that this theory is weird, because that would take many years. And if even it is caused violently (which is impossible), why  don't have I a Compsoghnatus as a pet?

A climate catastrophe, I don't think that caused the extintion of the DS. I am of the opinion that the Dinosaurs were Homeothermus like the Birds, not Poiquilothermus like turtles and alligators.

[Dante]

The gravity theory couldn't work because there were still huge animals around after the dinosaurs died out. Granted a great deal of species were much larger than present varieties (scorpions, dragonflies, crocodiles), but by the same token, many species have increased in size since then (horses and whales being two obvious examples). Though perhaps not to such a degree.

Upheaval is heaving upwards. In geological terms it strictly means a raising of part of the Earth's crust. I was using it more loosely, to mean 'a violent disruption or upset.' There is evidence - which I can't be bothered to go find - that the Earth was already experiencing geological troubles near the end of the Cretaceous period. Earthquakes, volcanos, etc. Throwing a meteor into that could only have made things worse.

You can't discount climate change however, because both the meteor and geological upheaval theories depend on it. The theory doesn't go 'A meteor hit and kill all the dinosaurs.' An event like that would have killed everything, and we know for a fact that a great many creatures survived. The theory goes that a meteor, volcano/s, or even both caused an abrupt shift in the Earth's climate, probably lowering the temperature by several degrees and blocking out a great deal of sunlight.

This is not to say that the dinosaurs were killed by cold. I have yet to make up my mind about whether dinosaurs were hot or cold blooded, though I suspect the latter (and incidentally, in case the terminology isn't familiar 'hot' or 'warm' blooded creatures are homeothermic and also called endotherms. 'Cold' blooded creatures are poikilothermic, also known as ectotherms). But in this case it has little bearing on the argument since both hot blooded (mammals and birds) and cold blooded (fish and reptiles) creatures survived. Had the dinosaurs become extinct due to their temperature control, we would also have no fish, crocodiles, lizards, insects... Actually I'm not sure about insects. Could soneone confirm for me whether they are hot blooded or cold blooded? I know I should use ecto and endothermic but it's force of habit...

Aaaanyway. The point is that climate change is the most likely reason for the extinction of the dinosaurs, as the evidence currently stands. Only those animals that were somehow resistant to cold seem to have survived, and evolved. What triggered this climate change is more open to debate. As I said, I favour the meteor/volcano theories.

There are other theories of course. That the newly-emerging mammals ate all the dinosaur eggs is very hard to believe. Especially since the dinosaurs had been eating each other's eggs for millennia. Some say the dinosuars all evolved into birds. Well they did, but evolution doesn't just bug off without leaving any scraps behind, otherwise we wouldn't have any sharks or dragonflies. It's not like they all turned into flamingos like in Rarg. I love that film, anyone else know Rarg?

Some people even blame shifting continents for the death of the dinosaurs. Yes, well, in Antarctica maybe. Not likely elsewhere.

[Jack Leaf]

Well, I think that the meteor is the most logical. A meteor big enough would stir up lots of dust, subsequently blocking sun light for long enough.

[Procyon]

I agree totally with you Dante... Ok with climate changes.

I have to say something to the gigantism theorie. The increase of size in mammals is just due to evolution, they don't have to compete with others big animals, like they did during the mesozoic.

Do you know the Brachiosaurus? There is nothing similar on Earth today.

The continent shifting is too slow to cause the extincion of a specie.

Oh, and  there was also a dinosaur in antartica (not so cold as today), I can' remember its name now.

Probably the change of climate and the blocking of light caused the extincion of some types of conyferes(?)= gimnosperms(?)(How do you say it in english?), and some types of bushes; the alimentation of sauropods and ornitisquius, and we know the rest of the story.

The extintion of some gymnosperms allowed the domination of angiosperm species (plants with flowers). The coniferes don't have a a protection for its seeds (fruits) and the gametes depend of climate factors to "move" and fertilize.

Notice the analogy of domination: Anfibians-Helechos (?),Dinosaurs-Gimnosperms,

Mammals-Angiosperms, so what's next?