Apart from a human with a rocket launcher, of course 
I’m thinking that with its combination of speed, power and ferocity, the t-rex could pretty much defeat anything alive today. Maybe the closest fight would be a hippo, a bull elephant or a large crocodile?
Look at the size of the thing, compared to a human. Its jaws alone are the size of a crocodile; a croc would be a tasty morsel, that’s all. One snap, bye-bye croc.
And, for all their aggression, elephants and hippos are still herbivores–you’re suggesting that an herbivore that comes up to the T Rex’s knee could possibly “give it a run for its money”? Please.
All the T Rex has to do is lean over and take a bite out of the elephant or hippo’s completely undefended spine with its set of 50 eight-inch-long teeth. End of story.
On its home turf, I’d bet on Orcinus orca. Hard to have a bad attitude when you are struggling just to breathe.
What food you eat has little to do with how well you can defend yourself. More people are killed in Africa by hippos than crocs, despite the latter being far more numerous. I think an African elephant with its tusks can convince a T-rex that having lunch somewhere else might be wiser choice.
I’m sure that Chuck Norris could take one out with one roundhouse kick to the face. That may even be why they’re extinct …
I wonder how much damage a rhino could do defending itself with its horn.
A full-grown polar or grizzly bear might be able to convince it to look elsewhere, even if it couldn’t prevail in a fight to the death.
Megatheria were around until quite recently (and some crazy cryptozoologists think they might still be), and one of them could probably have held its own against a t-rex. Even though it was smaller, it would have had truly formidable claws and teeth, very long arm reach, and bone-studded skin with thick fur.
Other recently-extinct mammals that probably could have given it a run for its money would be Elasmotherium and Arctodus. The former was a huge rhinoceros with a six-foot horn, and the latter a giant bear built for speed and with an incredibly powerful bite.
I bet there’s a fair number of viruses and bacteria that could take on a T. Rex and win. Does that count? Oh wait, they’re not animals! How about some intestinal parasitic worms?
Along those lines, I wonder if a black mamba, saw-scale viper or other deadly venemous vertebrate could kill a T. Rex.
You’ve been watching Disney’s The Sword in the Stone, haven’t you?
My money would be on the Stobor.
I thought the oxygen content of the atmosphere was somewhat different back then. How well would T-Rex be able to breathe in modern times?
Would a snake of some sort have enough venom to parlalyze the T. Rex?
A mad nest of killer bees?
(Somehow the image of a mad nest of killer bees attacking a T.Rex amuses me)
Like to see an Orca and T Rex go at it in shallow water, would be as even a playing field possible.
I remember reading in Sci Am that it’s now thought that t-rex actually “allowed” bacteria to grow in its teeth ( :barf smiley: ) in order to infect its prey to inflict even more carnage.
I guess any animal that was smart enough, and able to take out t-rex’s eyes first would have a chance.
Somebody probably got this idea because this is exactly what the Komodo dragon does. I don’t see how there could be any direct evidence, unless T. rex teeth have some unusually bacteria-friendly shape.
An modern animal hunting in packs might bring T-rex down. Imagine the shallow-water fight again, but this time, instead of one, or even several orca’s, imagine a large group of sharks. And sharks don’t even work well together, they just combine forces.
Mammoths were pretty large as well, but they were brought down by humans hunting in packs. Just imagine the hunting lore 'When Grandpa brought down a T-rex!"
To expand on QtM’idea, how about a T-rex with a several large flesh wounds from, infected with modern maggots?
Thanks yBeayf for the links. I knew about narwhals as a source for unicorn legends, but your Elasmotherium is a much more likely candidate.
Yeah. And I don’t see how having bacteria ridden teeth would help T-Rex be a more efficient predator. Wouldn’t it take a day or two at least for an infection brought on by a T-Rex bite to bring down the prey? Looking at the thing I wouldn’t think T-Rex would be inclined to wait that long for lunch, nor would he have to.
I rememeber hearing a theory a few years back that Rex may have been a scavenger. Is there any support for that?
A bull African elephant is about the same size as a T-Rex per Wiki. 13ft at the shoulder and 7-8 tons average weight. Compared to T-Rex’s 15-20ft to the top of the head and 5-7 tons weight.
The elephant’s shoulder comes up to the T-Rex’s neck, so I doubt that there’s going to be much leaning over to take a bite. He’s got big tusks, a sturdy frame, and a bad attitude. He can also outrun a T-Rex. The T-Rex may win the fight, but it won’t be any kind of a walkover.
Rhinos and hippos are much smaller than elephants, 2-3 tons instead of 7-8, and neither of them have weapons much more dangerous than the elephant tusk.
Piranha for one. I don’t see a T-Rex beng able to catch them, though he may be able to step on them.
Even if it’s one piranha against 1 T-rex - the big T will come away with a injury and the P will come away with a full belly