Hey again!

I've been thinking this question a lot. Especially the case of T-rex. I've heard lot of good points to support the idea of T-rex being hunter, but also many, and more fundamental-sounding arguments for T-rex being scavenger. But no, I'm not here to ask your opinion, I'm just telling mine. Of course, someone must - and I would be very surprised if no one so far - have figured this out before me, but anyways, here comes my theory:

Ok, all the carnivores, when they become hungry, are estimating the risks. The solution - whether dino goes for a kill or seeks the nearest carcass - is depending on which opportunity has smaller risks. Now I'll take T-rex and Velociraptor as examples:

When T-rex is hungry, she knows that she could find carcass pretty easily, thanks to her good sense of smell. She also knows that she is very, very scary and could scare those who made the kill away, or - if necessary - kill them. Also, some estimates are showing that T-rex was quite slow but had a good endurance, so she could have walked very long distances to carcass kilometers away. She have known also, that she is slow runner, so there wasn't too much "slow-enough-food". Of course she was able to make a kill, if the meal was slow and weak enough. But could such massive T-rex, as it was, have been "agile enough" to take down well armored dinos, which otherwise would have been "slow enough"? Or what if she falls down during the run?
SO, she may think, at least in most of the cases, that it is less risky to go and scavenge, at least with her features.

Velociraptor instead, knows that he is very agile, and he could chase down any animal. He also knows that he is quite smart, and has these killers claws, and most important - other cooperating velociraptors. But he also knows, that if he goes and tries to seek for carcass, he probably wouldn't find it fast enough (before starving to death), and when he finds, it probably isn't free and that he can't scare anyone away. But of course, if velociraptor finds a carcass by accident, he won't just walk by, cause it is free meal, but he won't actively search for them.
SO, he may think, at least in most of cases, that it is less risky to go for a kill, at least with his features.

What do I mean by "knowing"? Well, not actual knowing. It is something more like intuitive knowing, something that bases on instincts. You know, its been more useful for predators that their instincts says when it is safer to look for a free meal, and when not. Then, of course it is pretty automatic for the individuals themselves. So I'm not saying that they have been stopping wandering the risks whenever they came hungry, but their instincts tells it for them. It is like in evolution, within species that can't anyway have brains-big-enough to produce anything more special - like actual thinking - than basic body functions, those individuals who got such instincts that "played the game" via their own features, were more likely to survive and breed, etc...

Did you got my point at all? If so, what do you say?

I think what you are saying is that hunting and scavenging have different risks and rewards, and carnivore strategies will haev evolved in response to response to selection imposed by these. If so - I totally agree - behaviours coevolve with physical characteristics too, so there are many solutions to the problem of how to obtain meat (if you are a canivore) or food more generally.

I cannot comment on the importance of scavenging of either dinosaur you mention as this is outside my expertise, but would note that very few hunters around today are averse to a "free meal" if they find one. Of course the relative dependence on scavenging variaes a lot among species, but can also vary among individuals of a species.

Well you said you're not here to ask my opinion and then finish with 'what do you say' which rather does sound like asking for an opinion...

First off, you're really massively over simplifying things - finding a meal is not jsut about risk, it's about the potential souces of food, where they are, what other food might be around, what risks, what other carnivores, the evnivornment (and then times of day or seasons) etc. and it's all different for species and even indiviudlas at various times. Some lion populations hunt a lot, some scavenge a lot, cheetahs very rarely scavenge, vultures rely on it.

We know that both Tyrannosaurus and Velociraptor were both predators and scavengers - we have good fossil evidence for both ehaviours in both taxa (I actually published a couple of papers on the subject myself). Beyond that, it's hard to say much realistically about proportions of activities as the fossil evidence is not there and there's nothing in their anatomy or basica patterns that really suggest one over the other for either. That's all we know.