Quote from: Xenodog on Oct 14, 2013, 08:32:30 PM
I don't think we know enough - or will ever - of dinosaur behaviour to answer that.
But being so small in an enviroment with other bigger rexes doesn't seem like a great plan. What would they hunt also? Young herbivores would likely have adults defending them and scavenging is a dangerous hobby unless you have the jaws and balls to get into a fight over a carcass - something a juvenile probably wouldn't to a larger of it's kind. (T.Rex doesn't seem to have many competitors in it's range.)
I would also suggest a Utahraptor is more agile and dexterous than a young T.Rex.
A equivalent-weight Utahraptor would be longer and so appear bigger than a tyrannosaur and so in turn may have intimidation on it's side too though.
Just some of my two cents though!
Regarding what a young tyrannosaurid could hunt, there were definitely opportunities.
For starters, childrearing habits of dinosaurs are difficult to ascertain; even in the nestbuilding species it's unclear how long the parents paid close attention to their young. Sauropod youngsters were very likely left to their own devices immediately after hatching, and in any case it'd be very difficult for a whale-sized animal to defend tiny herdmates from fast, bear-sized juvenile tyrannosaurs. Finally, it's worth noting that modern predators frequently kill the offspring of animals that greatly outmatch them - cheetahs take baby wildebeest, lions take baby elephants.
There were also adult prey items that fit the bill. Ornithomimosaurs like Gallimimus were particular candidates, which might seem bizarre when you look at a lumpy Tyrannosaurus adult, but the youngsters were
very different, which I'll get back to...
What's very notable with Tyrannosaurus rex in particular is that there were barely any other predators throughout its range, as you say. The largest I can think of was Dromaeosaurus, which was the weight of a smallish dog (and we only have tooth evidence of even
that being around in the same time and place). This leaves a
huge gap in the ecosystem, no adult predators between 15 and 5000 kilos... and one that's conveniently plugged if you assume the young rexes were hunting.
Anyway. Tyrannosaurus had one of the most peculiar life histories of any dinosaur we know. Particularly if feathers were involved, you might not even recognise a young rex and an adult as the same species (this even applies to the bones, 'Nanotyrannus' is very likely a young rex). While the adult was built for sheer overwhelming power, ridiculously muscled and equipped even for an apex theropod, the juveniles were long-legged and lithe. Particularly, they were some of the fastest sprinters among predatory dinosaurs - we can tell this from the leg configuration, as the tibia is significantly longer than the femur, and the feet extend this trait even further. They were also lightly built, with a compact centre of gravity.
To put this in perspective, we don't see these features exaggerated to such a degree even in most dromaeosaurids, particularly the big ones like Utahraptor. To get back to my earlier point, young rexes may have been very well matched with ornithomimosaurs.
I do agree with you that Utahraptor would've been more imposing though, for the reasons you state. Wouldn't surprise me if they had some form of feather display to deter rivals either. And their short 'wings' may have provided a boost to their balance, aiding agility.
