Dinosaurs & Science

[Ibrahim]

Wow... I am in a way surprised and in a way not. I've grown with the idea of the dinosaurs as overed with scales animals. On the other hand, having in mind their relation with the birds, I expected a diversity of colours.

I think we should accept many of these animals had something between feather and scales on them. I still think there were dinosaurs covered with scales and of course others with furs. The same can be said about warm/cold blooded question, perhaps.

Btw, what is the chance for the T-rex of having a fur like this? Apart from being bipedal there is not much in common between his skull and that of a chicken... Personally, I think that T-rex looked like a huge bipedal reptile (scales dominating over the fur/feather though I would not be surprised if they is some fur/feather). I feel slightly incompetent to judge whether it was cold or warm-blooded. Warm-blood makes him closer to the birds and would make him and active hunter but being a cold-blood would make him more resistant to hunger and the harsh environment of the Cretaceous. His giant size also favours the second since the later species of the mammals and the terror birds never reached the size of the dynasaurs. Tail is also absent from the typical birds. I tend to think that the birds are simply one of the branches of a larger family of warm-blooded dinosaurs whilst others were cold blooded (but it is hard to say the ratio between the warm and cold blood dinos, I think).

In short, I opne the debate what is the image and the blood for the bigger dinos like T-Rex and some other gigantic carnivores and herbivores from... say, the Cretaceous?

well, you need experience in dinosaur anatomy before deciding that. just looking at a chicken and a T-rex side by side isn'tenough. a T-rex's skull is very similar to a birds, once you look carefully: both have antiorbital fenestra,a sclerotic ring in both (none have been found in T-rex, but the ring is rarely preserved, and as other relative were found with them, its likey and birds usually have them); both are diapsid, poposses a mandibular fenestra, etc.

the postcranial skeleton shows FAR more similarities: the presence of a furcula (wishbone), the tridactyl foot structure, reduction in digit numbers, penumaticized bones, a process on the humerus (found in all dinosaurs), etc.

as to whether Tyrannosauroids had feathers: well, it really depends on the size of the animal: a fossil tyrannosauroid, Dilong, was about 5.5-6 ft, and it was found with feathers. surviving skin impressions of Albertasaurus, a very close relative to T-rex that was 30 ft long, show only scales. the descrepency is due to the fact that as the animal's size increases, the animal is less able to shed heat (surface/volume ratio goes down), thus natural selection favors the secondary loss of feathers in the larger forms. consequently, T-rex, at least as an adult, had scales, not feathers. it also means that T-rex was almost certainly* "warm blooded".

also, T-rex is a coelurosaur: its thus actually FAR closer to birds than to crocodiles. though its actually pretty basal by coelurosaur standards: Dromeosaurs and troodonts are even closer, with over 30 different basic traits being shared with the birds. (fused sternum, uncinate processes, wing feathers, semilunate carpals, and a list of other traits I can't be arsed to remember).

*as in 99.999% certain

EDIT: its highly unlikely any dinosaur was truly ectothermic; and as far a I know, all papers that supposedly "prove" ectothermy are either outdated, or, if they come from John Ruben, pretty much full of it.

[Prince Cobra]

Ibrahim, how does the warm blood affect the behaviour of the dynosaurs? For me this means a constant need to eat (especially for the carnivorous species)... It's not like the snake: you catch a big prey, eat it and then you can wait for the next meal a looong time...

[Ibrahim]

warm bloodedness simply means, as you say, a higher metaolic rate. this means that the animal waill be active throughout the day, hunting, mating, etc.

this has a far greater advantage than any disadvantage: the animal can regularly, and constantly find food, mate, defend its territy, etc, since the animal no longer needs to bask in the sun or hide in the shade as much. that was the edge archosaurs (like dinosaurus), and later mammals, had over everything else.