why did the dinosaurs not evolve back

So why were there no ice caps at the poles then? maybe because the earths axis was of one of much different as it is now?

No, the axis was the same. The continents were in a different configuration, though, and the atmosphere had more greenhouse gasses to hold heat.

Really, consider why we have polar ice caps now. At the North, we have a basically circular ocean with limited exchange with the rest of the seas. This allows cold water to build up in the north.

In the south, we have a basically round continent which allows snow to build up into ice sheets.

This configuration was not present during the Mesozoic.

No. Temperature alone explains it pretty nicely.

Venus has an almost vertical axial tilt yet no polar ice caps. The massive temperatures have something to do with that.

Likewise, the amount of ice at Earth’s poles don’t directly depend on its axial tilt.

Look: you’re trying to create something that merely sounds plausible. That’s nice and all, but you should try looking at actual facts instead of sticking stubbornly to an idea that doesn’t fit the data.

For one, the amount of tilt in the Earth’s axis has been studied at length. While it has varied a small bit, there’s no evidence it has varied nearly as much as you suggest. Worse, a meteor impact that could kill the dinosaurs without killing all life on earth would simply be too small to affect earth’s tilt.

And as noted above, theories about absurdly large plants and flooding is pretty easily debunked by the geologic record.

Long before. In fact really, we shouldn’t be lumping the two together as “dinosaurs”', just a mistake by the guy who coined the name.

Are there some basic books that we can recommend that breakneck read about evolution, dinosaurs, mass extinctions, the organisms and geology of the K-T period, and the K-T mass extinction? I think that breakneck is going to need to learn a lot more than we can explain in one thread. Also, breakneck, I’d like to suggest that you take a course on writing. I mean ordinary nonfiction expository writing, not fiction writing. You need to do a better job at expressing yourself. If you’re out of school, see if you can find some place that will teach adults such classes.

Never mind reading some books; a scan thru the very high-level Wikipedia article on dinosaurs should at least provide a foundation and launching point to some of the core concepts the smart dopers here have already provided. Even that, tho, will take some effort.

Yes. The presence of ice at the poles has much more to do with the configuration of continents, how ocean currents transfer heat around the globe, and the level of greenhouse gases in the atmosphere than it does with axial tilt. Since the K-T event the climate has varied from much warmer than today in the Eocene to much colder during the Pleistocene all with essentially the same axial tilt.

Okay, after the large dinosaurs were taken out of the picture mammals evolved to fill the niche of large animal in both the prey and predator groups. The largest land mammals have been dwarves compared the giants of the dinosaurs.

So question one is what allowed the large land dinosaurs to become so much larger than any land mammal and what factor(s) drove that as an adaptive niche to fill? This article offers the speculation that the air sacs that birds still have were the key in allowing some dinosurs to become so large, allowing for greater cooling and from an engineering standpoint, lightening the load, that and long necks:

Fine. It doesn’t answer the second part though. What advantage was there to being that large?

That I suspect has a decent WAG out there. The next question though is more interesting, is then informed by the first two, and is close to what I think our op is asking.

Got it that the larger animal niche was mostly filled by some relatively mega-mammals. But birds still have that structural advantage and some birds have indeed gotten a bit big in eras since … but emu and ostrich big, not much bigger. Birds have also gotten smart. Corvids are freaky smart, especially given the size of their brains. So given that birds have same structural advantages that allowed for mega size that their dinosaur ancestors had, and that they have the capacity to develop significant intelligence out of a brain that does not need to even weigh that much, why in all this time, throughout all the environments and ecological systems that birds have existed in, have no birds evolved to fill the very large animal niche?

Why aren’t there any birds that have become even very large mammal sized, let alone megadinosaur sized?

how did they arrive at the growth rate? surely fossil records aren’t accurate to the day?

Here’s one speculation as to what was special for the dinosaurs that birds have not had:

Not sure I buy that though.

Well Wendell, thanks for the advice. It s a freakin forum , not an essay . Really thanks hahahahaha these means s*it to me mearly entertainment . Like I’m going to spend time on proofread this crap.

So you think that you can write any nonsense you feel like, but we have to give you well-thought-out replies? I think you’re one of those posters who think that because you write very fast that we can read your posts very fast. We can’t. Your posts are hard to understand. Furthermore, most of us don’t spend very much time on things like grammar and spelling because we have an enormous amount of practice in writing. We can do a quick check of our posts just before we hit “Submit Reply” to correct any small mistakes. You clearly need more practice in writing.

I don’t think that asking breakneck to read the Wikipedia entries on the appropriate subjects is going to be much use. Those entries assume some basic knowledge that he doesn’t have. He needs to read some lower-level books on these subjects. I don’t think, for instance, that Stephen Gould’s books are going to be the best place to start.

I don’t recall any A-B-A or A-B-C-A successions on the fossil record. That would have been worth studying. But I might be wrong.

well check it out wendell. The caps are probally making your skin curl. You sit there and tell me these things i need to do or that i am not . I got only one thing to tell you to do … That is you dont need to read my posts . Plain and in simple english hahahaaha true i dont have enormous amounts of practice in writing . But what i do for everyday doesnt allow me the luxury to brush up. Like i said entertainment

Agreed.

Excuse me. Between breakneck’s poor writing skills, lack of consideration for the needs of others who might be trying to read his/her posts, etc., and the snark directed at him, there IS still a set of open questions that his post minimally evoked.

I can guess what the advantage to very large might be - large can be a defense as much as fast or armored can be, especially if foraging is abundant. And large prey drives adaptive increase in size from predators to neutralize that defense.

But WHY have birds so rarely returned to large sizes and then to large sizes that are not even very large by large land mammal sizes, let alone by the bar their ancestors set?

Differing competition. After the K-T event, big brains became the fashion rather than big bodies.

My guess? Hollow bones. Once you’ve evolved those, it’s hard to evolve back.

Dinosaurs had hollow bones.

Even the largest terrestrial birds today are descended from flying species. I would not be surprised if there are any number of developmental pathways needed for flight which constrain the possibilities for future adaptations.