The correlation between aggressive behavior and succes of a theropod

UCMP 118742

I noticed this thanks to Rex Fan's post about how Tyrannosaurs and Allosaurs seem to be a lot more aggressive than other theropods. Anyway, that got me thinking and I realised something. Wherever a new, more aggressive species came in contact with a less aggressive species, the more aggressive one became more succesful after some time. And there are examples all over the world. North America was ruled by Carcharodontosaurids (Acro, Siats etc.) during the early cretaceous, but eventually they were outcompeted by the Tyrannosaurids, but why? Acrocanthosaurus and Siats both weighed about 5 tons and the Tyrannosaurids at that time were a lot smaller. Albertosaurus capping at 3 tons and Gorgosaurus at 4 (As far as i know Daspletosaurus was later, but i'm not 100% certain) so they didn't have the advantage in body size. But those species, just like Tyrannosaurus rex were a lot more aggressive and would've gone out of their way to attack something else. The same thing happened in South America. Carcharodontosaurids ruled it for almost the entire Cretaceous, but in the last few millions of years, they were outdone by the Abelisaurids. We have evidence that both tyrannosaurids and Abelisaurids were very aggressive animals, of course Carcharodonotsaurids were aggressive animals as well, but probably a lot less than Tyrannosaurids and Abelisaurids. Here's a little example of how that would work: 

Theropod A finds the unguarded nest of Theropod B. He knows that the parents could be back anytime and decides to ignore it.

Theropod C finds the unguarded nest of Theropod D. He knows that the parents could be back anytime, but he has the chance to destroy an entire geneartion and goes out of his way to kill the hatchlings. (Then the parents arrive and kill him, but still, he took an entire generation with him)

If that process repeats many times, eventually Theropod C will have the highest population.We can observe the same thing in Late Jurassic Europe where Torvosaurus and Saurophaganax were outdone by the smaller, but more aggressive Allosaurus.

I'm bad with explanations, but I tried my best. What do you think about this? Is there actually a correlation or was it just a coincidence?

Lord Vader

Entirely possible. Probably the best explanation yet to the Tyrannosaur's success.

Alphadino65

Yours explanation proves to be very reasonable.  

I also think that maybe the tyrannosaurids and abelisaurids had different breeding habits than the carcharodontosaurids.  Perhaps they cared for their young for a longer period of time, or layed more eggs, or watched over the nest more frequently, or any combination of the three.

Rex Fan 684

Seems completely legit. I can say I agree with this. 

Acro Rex

it's interesting for sure, but i don't think these smaller theropods would go out of their way to attack larger ones, such as an allosaurus attacking a full grown torvosaurus. Not only is the megalosaurid stronger, it's....well...bigger

A prime example of this is the big cats and other animals of Africa. We don't see the wild dog, a fiesty little animal, going around and attacking the lions. Nor do the hyenas. But if a lion sees a hyena pup, it will kill it. Gets rid of competition. Same goes for the hyena. It all boils down to competition, and eliminating future threats.

Even male lions that take over a pride, will kill the cubs of the dominant male. They won't even eat them in most cases, just kill with a quick bite to the neck...then leave them for the scavengers.

Acro Rex

it's interesting for sure, but i don't think these smaller theropods would go out of their way to attack larger ones, such as an allosaurus attacking a full grown torvosaurus. Not only is the megalosaurid stronger, it's....well...bigger

A prime example of this is the big cats and other animals of Africa. We don't see the wild dog, a fiesty little animal, going around and attacking the lions. Nor do the hyenas. But if a lion sees a hyena pup, it will kill it. Gets rid of competition. Same goes for the hyena. It all boils down to competition, and eliminating future threats.

Even male lions that take over a pride, will kill the cubs of the dominant male. They won't even eat them in most cases, just kill with a quick bite to the neck...then leave them for the scavengers.

Acro Rex

it's interesting for sure, but i don't think these smaller theropods would go out of their way to attack larger ones, such as an allosaurus attacking a full grown torvosaurus. Not only is the megalosaurid stronger, it's....well...bigger

A prime example of this is the big cats and other animals of Africa. We don't see the wild dog, a fiesty little animal, going around and attacking the lions. Nor do the hyenas. But if a lion sees a hyena pup, it will kill it. Gets rid of competition. Same goes for the hyena. It all boils down to competition, and eliminating future threats.

Even male lions that take over a pride, will kill the cubs of the dominant male. They won't even eat them in most cases, just kill with a quick bite to the neck...then leave them for the scavengers.

Acro Rex

double post..

Raptor-401

Quadruple post...

UCMP 118742

Thanks guys. Yeah, I know that it still needs some polishing, but it does seem like a plausible theory for the largest part.

Rex Fan 684

Acro Rex, are you familiar with the honey badger? It has been observed taking on and driving off lions, despite being many times smaller. Why? Because badgers are like weasels from hell. They' down. Also, hyenas are commonly seen harassing and taking on lions. Sometimes, being smaller creates a more aggressive attitude. It helps to make up for the animal's smaller stature. Just a thought.

Carnosaur

I agree with what Acro said, African dogs themselves are much smaller then the hyena. However, the Hyena isn't that much smaller then the lion, and confrontations between the two are very frequent.

As for your honey badger anology, they are mainly acting in self defense - self preservation. I've noted those little animals are hyper aggressive, yet they do not go actively seeking confrontation with the larger carnivorous mammals. Nor do they challenge them for a zebra carcass.

I Believe what we have evidence of here, with the Tyrannosaur and Allosaur bite marks on the fossils, is evidence of predation, or just a territorial confrontation. Perhaps even part of a mating ritual, for we have no idea how violent these animals were in their breeding season.

Reptiles, crocodiles and lizards in particular, can be rather violent during mating season. They bite down on the back of their partners neck, assuring a better grip on their mate. I believe this is some of what we are seeing in the fossils, but not really being able to tell gender at this point, that's just a theory.