Quote from: DoomRulz on Oct 31, 2013, 12:48:34 PM
Quote from: Vertigo on Oct 28, 2013, 10:35:57 PMEvery dinosaur had an upright, active stance like birds and mammals do.
I'm not sure the quadrupedal herbivores would fit that description.
By 'upright' I mean they held their legs directly beneath their bodies in a pillar-like manner, rather than the side-sprawled manner of reptiles. I was trying to avoid saying 'erect' as this makes me imagine them walking along on a set of giant penises.
The advantage of a sprawled posture is that it allows an animal to go from sitting to running almost immediately, essential for a cold-blooded animal that spends most of its time resting.
The downsides are that it's a drain on energy as it uses more muscle power to move quickly, and as the locomotion compresses the torso, it limits (or even negates) their ability to breathe while running. Warm-blooded animals gain far more of their energy from breathing than cold-blooded ones do, so they need an upright posture to achieve peak performance.
All dinosaurs had this upright leg configuration, and aside from my point about this differentiating them from the classic definition of 'reptile', it marks them out as a very active group of animals. You can pick out an outdated piece of palaeo-art very easily, as they often depicted the quadrupeds with a sprawled leg posture to match the sluggish, cold-blooded lifestyle they were assumed to lead at the time.
Quote from: DoomRulz on Oct 31, 2013, 12:48:34 PM
Spoiler
Quote from: Vertigo on Oct 28, 2013, 10:35:57 PM
Quote from: xeno-kaname on Oct 28, 2013, 04:41:34 AM
I believe it. Most people think about T-Rexes shrinking down because of evolution, though. That's probably the wrong way to look at it. The big dinos are the ones that probably died out, and the small ones evolved and started to develop feathers and wings at some point.
Tyrannosaurs kept getting bigger as time went on! Rexy itself was the apex of the family - the largest by a considerable margin, and the last one before the mass-extinction event. This is a trend that happened in several other dinosaur groups immediately before the extinction, particularly in North America, and we're not sure why. It was terrible timing, as on land only small animals survived the apocalypse.
I think T.Rex in particular had to grow as large as it did in response to the prey items of the day. When you're going after creatures like Triceratops, Ankylosaurus, Alamosaurus, and Edmontosaurus, size will come in handy.
Certainly true, predators tend to evolve in response to their prey (herbivores are less tied to their predators' evolution, as generally the percentage taken by predation isn't large. Then again, most herbivores in history haven't had to contend with Tyrannosaurus rex...). The question is why the herbivores needed to grow so huge, and why many smaller animals became marginalised or extinct in the last age of the Cretaceous (the Maastrichtian).
My guess is that it had something to do with their diet. I know certain types of grasses appeared at some point in the Cretaceous, but am not sure exactly when. A larger stomach aids digestion, so if the Maastrichtian herbivores were needing to cope with a wider variety of food, or just tougher stuff, then it might explain the growth spurt.
Quote from: Xenodog on Oct 31, 2013, 05:05:19 PM
Yeah that's most likely I.M.O. I also wonder if certain individual dinosaurs in a species, despite their more primitive brains, had the ability to specialise in certain prey items that were unusual or dangerous like some modern predators.
Dinosaur intelligence is an
incredibly tricky subject, I ranted about it a little while ago. Probably fair to assume that any dinosaur with a lower EQ than a crocodile wasn't terribly bright, and many of the groups may be comparable to each other, but other than that, the only accurate assumption is that we don't really have a clear impression of what they could do. My two-minute bout of googling suggests that avian intelligence is governed by a region of the brain called the nidopallium caudolaterale, and I've never seen a study of this in dinosaurs.
But no dinosaur brain is entirely comparable to that of a bird, and they probably aren't comparable to crocodiles either, so until we put a Compsognathus through a maze to find some cheese, I wouldn't put faith in any assessment of dinosaur intelligence.
Intelligence aside though, it's true that the modern avian brain structure was constantly developing throughout Coelurosauria and well into the early birds, so the 'primitive' label is indeed accurate as a comparator to their descendants. I seem to have lost my notes, but I dimly remember that a tyrannosaur brain is around 5% of the way from reptile brain structure to bird.
It's important to make the distinction that this doesn't necessarily have anything to do with intelligence though, some reptiles can be surprisingly smart. I remember reading a study in which a heated-up tortoise was put around the same maze as a rat, and it solved it more efficiently - whereas it fared poorly in rooms below its peak operating temperature, the state that all previous reptillian studies had been performed.
Anyway. Specialisation is a result of learned behaviour, so I suppose a lot of it depends on how long theropods were raised by their parents. Aside from this resulting in parental teaching of hunting techniques, animals with extended rearing periods tend to have more flexible behaviour, less programmed by instinct (this is just me speculating based on animals I'm familiar with, so feel free to call bullshit on that one). But I see learned specialisation in animals as disparate as great white sharks, lions, orcas and harris hawks, so it wouldn't surprise me to see it in dinosaurs.