Evidence for large abelisaurs coexisting with Spinosaurus

Adam Khor

Just a measly bone, tho, so it may have looked very different from the pic. Still, cool pic...

http://www.express.co.uk/news/science/623439/Dinosaur-new-discovered-bus

Linnaeus

There may have been diverse large predators which all lived more or less in close range with Abelisaurus; but carnivores of different species do not necessarily prey on each other. The real competition would have been over food. If there were not enough herbivores around to satisfy the hunger of all the carnivores, then vicious battles for prey may have occured.

Linnaeus

Post script: which is to say, that many predators, as long as their bellies are full of herbivore meat, will leave other predators alone. Plant-eaters are in general easier to kill, anyway. But in times of famine...well, the big carnivores would have probably not hesitated to attack other ferocious species and maybe even members of their own.

Adam Khor

which is to say, that many predators, as long as their bellies are full of herbivore meat, will leave other predators alone.

Actually, most predators tend to be highly intolerant of each other; apex predators in particular will go out of their way to hunt down other meat-eaters. When it comes to large mammalian predators, they usually won´t even eat their carnivorous prey, but rather abandon the carcass, so clearly they are not hunting them out of hunger, but rather to eliminate competitors or quite simply, out of pure dislike.

Some examples: African lions will go to great lengths to hunt down and kill any hyenas (which they seem to despise particularly, to the point that male lions will make a sport out of offing them), leopards, cheetahs, wild dogs and lions from other prides. So intense is their pressure on lesser predators that some species such as wild dog and cheetah can´t really thrive in places where lion are particularly abundant, even if there's plenty of prey for all.

Siberian tigers will do the same to wolves; when the tiger was abundant, wolves would migrate to other lands to avoid decimation (as tigers will relentlessly go after wolves if present). When tigers almost became extinct, the wolves slowly took over, much to the surprise of local people who had rarely if ever seen one within their lifetime.
When the tiger was reintroduced, the wolves were once again chased away by tigers, with some being killed (and ocassionally eaten).



Also, Siberian tigers are notorious for including Asian black and brown bears in their diet, to a considerable extent. They kill even the adult brown bears which are bigger than they are and extremely dangerous.



In turn, the brown bears themselves will prey on tigers if the opportunity arises.



In India, tigers kill dholes, leopards and bears, and they probably killed wolves too when both species were more numerous; in North America, grizzly bears will black bears, wolves kill coyotes, and cougars kill wolves.

And in Europe, lynx (both northern and Iberian) will ruthlessly hunt down any marten, stoat or polecat they can find, and they seem to particularly despise fox, so much in fact that hunters would sometimes lure lynx into ambush by mimicking the scream of a rabbit in distress, because the lynx would assume there was a fox hunting nearby and quickly show up to dispatch it.

Birds are the same; owls will prey on hawks, hawks and eagles prey on owls, and large owls prey on smaller owls. It IS dangerous, but they don´t seem to care; put up one of those fake owls used to scare corvids away and diurnal raptors will come and attack it, even if an owl is perfectly capable to seriously injure or kill an attacker.

So there really is no such thing as professional courtesy among predators. They live in a constant battle with each other. And this has been known since ancient times; not a recent phenomenon.

As for herbivores being easier prey than carnivores, that too is debatable... some herbivores may be, but lions have much more trouble killing large buffalo, hippo or roan antelope than they do killing hyenas or leopards, and there has never been a reported case of a leopard killed or even seriously injured by a cheetah or a jackal, whereas the herbivorous porcupine has been the cause of many leopard deaths. No way to generalize here.

Regarding dinosaurs- specifically the carnivorous ones from northern Africa-, it used to be believed that they lived in a sort of unbalanced ecosystem because the fossils of plant-eaters were seemingly so rare, but now, with Spinosaurus being reinterpreted as an aquatic animal, at least we know one of them was feeding on aquatic prey thus avoiding competition with the other giant theropods.

Cacharhodontosaurus was definitely a land-dwelling hunter, and it may have been a sauropod specialist (there are at least two distinct kinds of sauropods from the same regions and age), whereas Deltadromeus is still known from very fragmentary remains only and it may even turn out to be a giant plant-eating theropod (it has been compared to Limusaurus, which was a toothless herbivore despite its ceratosaurian affinities).
I'm not convinced about the so called Sauroniops recently described as yet another carcharodontosaur from the same regions. The remains are really measly; it may be just another Carcharodontosaurus for all we know.

And same goes for this new abelisaur. Seeing as all we have is a leg bone, we may be assuming way too much. May not even be a top predator; may be a fish eater or a specialized scavenger or even another herbivore. Who knows? I think it's too early to become excited. More remains are needed to answer the riddle.

Linnaeus

Please note that, in my latest posts, I was not categorically referring to all predators; remember my statement that they do not NECESSARILY prey on each other. Some species seem to be indifferent to each other, and if they do not exactly co-exist in friendship, they at least ignore each other. Others, as you so correctly say, apparently have an ingrown dislike of each other, and live in constant antagonism. Yet I would like to emphasize that this antagonism may not be INBORN: there are innumerable documented cases of baby animals belonging to theoretically incompatible species, which when raised together never seem to develop that antipathy/hatred that might have been inculcated in them by their parents, had they been raised "at home alone". It's very interesting to observe that many, if not most, juvenile predators are TAUGHT to hunt by one or both parents.

It may well be that hatred and prejudice are ACQUIRED characteristics. This is so at least among humans.