Is progress real?

[Ibrahim]

Cold/Warm blooded is a little outdated. Great White sharks are one of many animals that shares traits of both. Really the only difference is one generates it own heat, the other relys on external heat. Great Whites use muscle generated heat to keep its body temperature above the surrounding water's.

Same with dinosaurs. The only ones that are usually considered warm blooded are therapods - evidence is directly or indirectly supported for endothermy/homoiothermy/I can never remember the diff .

much better. now on with the rest of this post :

correct regarding the classification, metabolism wise; specifically, an animal's metabolism is devided in 3 grades:

ectothermy/endothermy: where the metabolism comes from
Homoiotherm/poikilotherm: the level of variation in an animal's metabolism
bradymetabolic/tachymetabolic: how high or low the resting metabolism is. I can't remember which is which.


as to dinosaur metabolism? what you said is incomplete: its now known that all three were fairly high: high metabolism, low to medium variation, and self generating heat. the reason we know this are as follows:

1)the animals most certainly had 4 chambered hearts; all living archosaurs (Birds and Crocodiles) do as well*. and genetic and embryological research has shown that the Crocodilians were natively warmblooded, then became cold blooded-like the naked Mole rat did. 4 chambered hearts are more powerfull/efficient than 3, so more metabolic energy is available for the dinosaur.

2) knowing what we now know about Sauropod and Theropod anatomy, they also had an avian respiration system-in fact this is the most efficient respiratory system possible. Ornithischains may have had it too, but no hollows in the vertebrae have been found in such animals (that's because in birds, the airsacs are in vertbrae as well as in the body cavity). this doesn't mean that they ornithischians had none: embroyologically, the airsacs in birds at first appear outside the bone, in the chest and abdominal cavity only.

3)its well know that theorpoda, especially Coelurosaurs, had feathers. even T-rex was likely a fuzzy fellow (at least as a hatchling/juvenile; after 1 ton mass, the feathers are no longer needed).

4)growth rates in Dinosaurs were closer to that found in warm blooded than cold blooded animals. that said, it was unusually slow**-closer to marsupial rates of growth than birds or mammals.

5)ecologically, it makes no sense that cold blooded animals would dominate warm blooded animals (in this case dinosaurs suppressed mammals, preventin them from occupying the larger niches). this doesn't even happen today. the only reason Komodo Dragons are dominant in their islands is because there are no warm blooded predators, and the now extinct Megalarnia prisca was rare, slow, and ecologically worthless. cold blooded animals do however have a good hold on semiaquatic environments, but as non-avian dinosaurs were almost totally terrestrial, I only worry about the Komodo.

6) more energy is required for the active, erect legged, bipedal stance of the T-rex or the Coelophysis than being squatted, as in a lizard's case (believe me, erect legs really are energy wasting), and the physics of many dinosaurs-especially the small and the early, are built in a cursorial manner-or great for running and agile moves. Crocodiles are a partial exception.


*However, Crocodiles also have a valve that allows the heart to act as a 3 chambered heart, especially when under water.
**this paper touches on the presence of growth rings as well as fibro-lamellar bone, which collectively indicate this. it also covers more stuff, but I invite you to read it


EDIT: I think the dinosaurian parts ought to be moved to the science forum, in the dinosaur thread.