undiscovered predators:What could involve South America

Hmmm... Giganotosaurus and Ekrixinatosaurus lived in the Late Cretaceous South America... and I really don't know about any other undiscovered yet... if that makes any senses...

Interesting. Giga and Ekrix are from the Mid Cretaceous though. Still an interesting theory, and entirely possible. I personally doubt it, it seems as though Rex, Spino, Giga and Charcar are the size limit for theropods, but that's just my opinion.

Ok, and I was talking between 80 and 65 million years. I see what you mean by Late Cretaceous.

Ah, ok. That's very Late Cretaceous, haha.

I guess. Some people have different thoughts and opinion I guess.

Giga and Ekrix lived about 90-115 million years ago(alongside Mapusaurus and a few other theropods). Aucasaurus(16-20 ft) lived 80 million years ago and Tyrannotitan(36-40 ft) lived roughly 85-95 million years ago. I agree though, there weren't really any theropods over 30 ft between 65 and 80 million years ago.

What could have causet that decrease in the size of predators? Maybe climatic ghanges, that brought to less vegetation, so less prey?
Just a guess.

Many of the really giant sauropods were gone by the late Cretaceous. Puertosaurus was the last really large one. Titanosaurus, Argentinosaurus, and the others were all extinct. Most of the sauropods around at the time were like Saltosaurus(36-40 ft). Predators did not have to be all that big. Now, that said, I do think there was something there. However, don't forget about carnivores like Megaraptor and Aerosteon(Megaraptor was 26 ft and Aerosteon was 30 ft). They lived about 80-85 million years ago. I'd say the really big predator was either an abelisaur or a tyrannosaur(since it's possible that the megaraptora were tyrannosaurs). I doubt it was a carcharodontosaur or spinosaur since they were all probably extinct by then.

Yes, I actually see Megaraptors as Tyrannosauroids. But, then, the Big Sauopod disappear, is due climal changes, right?

Most likely. When species die out(or show up), it's usually due to a change in climate.

True. Well, Megaraptor and Aerosteon weren't small thingies too ;).

No they aren't and I wouldn't be surprised if they were pack hunters.

Me too. They would be fearless killers.

Indeed...

Perhaps Aerosteon and Megaraptor had a larger cousin(tyrannosaur) that was about 36 ft long or so and it was the top predator. Guess we'll have to wait and see what's found.

Right. Nothing's sure in paleontology world. 

That's possible, and i agree DinoSteve

well i looked after a few thing.

at first the tyrannotitan lived before the giga,and the megaraptor lived at the same time with giga.

an other intresting(at least for me) thing that i found that the megaraptors and abelisaurs become smaller after the megaraptor and ekrixinathosaurus.thats possibly because the food.probably those two dinosaur family hunted for the amargasaurs,and after they extinct they start to hunt for the smaller saltasaurs.thats why probably they become smaller and stay at the same size.

so this undiscovered top predator could be a giganotosaur.

i dont think that the temperature effected to the south american dinosaurs.i saw some arts from the 90-75 million years earth and notice that south america become more close to the equator.