Ceratopsian Hadrosaurian question

Allosaur

Being a theropod fanboy (hey, first to admit it) I don't know a whole lot about the menu items AKA everything else.

So I have a question.

Anyone know of any evidence (direct evidence) of massive heards? I'm trying to get my head around Curries idea of rex packs, and keep fetching up against the intellectual wall of how much food such a pack would need.

Adam Khor

There is plenty of valid evidence, I would say. There are several cases of "ceratopsian graveyards" in which dozens, hundreds or even thousands of individuals of different sizes and ages are found all together, probably as the result of mass drowning or some other catastrophe. Kinda like today in Africa, when huge herds of wildebeest or zebra try to cross a river and many drown and their bodies all end up in the same place.
The fact that in these graveyards, most if not all of the fossils belong to the same species, suggest that they were living and/or migrating in herds. There's also the fact that ceratopsians had elaborate horns and frills that seem to have had a social function as well as being weapons (the horns). This makes more sense on a herding animal than in a solitary one.

As for hadrosaurs, I think (but I may be wrong) that mass graveyards have also been found. But even if they haven´t, there's some evidence that they at least bred in colonies, with many adults tending to their nests and young in the same places, like modern day seabirds.
Although it is possible that these hadrosaurs got together during breeding season to offer better chances of survival to their young, one must consider that they were, even as adults, much more vulnerable to large theropods than heavily armed ceratopsians or ankylosaurs, which means that it makes sense for them to stay in herds all or most of the time, as there's safety in numbers.
I think there are plenty of footprints too that confirm that hadrosaurs (and iguanodonts) traveled in herds.

If tyrannosaurs did indeed hunt in packs (which I´m not so sure about, but then again it may be), it is possible that they followed migrating herds from a distance, picking on the dead, the weak, the injured and all those that separated from the herd for whatever reason. It would be much easier and safer than attempting a full charge against the herd- ceratopsians were no wimps, and large adult hadrosaurs were massive and could possibly trample or crush a light-boned theropod if it got too close.

Of course, that's just what I think...

Allosaur

Adam Khor wrote: »

If tyrannosaurs did indeed hunt in packs (which I´m not so sure about, but then again it may be),

One must first deffine "pack" in terms of size.

ceratopsians were no wimps, and large adult hadrosaurs were massive and could possibly trample or crush a light-boned theropod if it got too close.

Of course, that's just what I think...

I imagine them more like Musk Oxen. Adults on the outside, kids on the inside, all the pointy bits facing towards the threat til it gives up and goes away.

Rubecula

Adam Khor wrote: »

If tyrannosaurs did indeed hunt in packs (which I´m not so sure about, but then again it may be), it is possible that they followed migrating herds from a distance, picking on the dead, the weak, the injured and all those that separated from the herd for whatever reason.

I don't really like doing a direct comparison between dinosaurs and modern day reptiles as they are are about alike as cheese and chalk in my own humble opinion, however, I would tend to think that Trex probably hunted in groups not packs when the need arose. A bit like Komodo dragons. I am not saying they had a poisonous bite, far from it. I just see them using similar 'tactics' on a much larger scale.

Probably wrong, but that is just how I see it.

Adam Khor

Allosaur wrote: »

One must first deffine "pack" in terms of size.

Size really is not the issue. In order to qualify as a pack, the members have to work coordinately to hunt their prey, like wolves do today. (Lions, hyenas etc are also pack hunters but their "packs" receive special names, such as prides or clans).

A group of animals, regardless of number, is still not a pack unless they hunt together.

Allosaur

Adam Khor wrote: »

Size really is not the issue. In order to qualify as a pack, the members have to work coordinately to hunt their prey, like wolves do today. (Lions, hyenas etc are also pack hunters but their "packs" receive special names, such as prides or clans).

A group of animals, regardless of number, is still not a pack unless they hunt together.

A pride consists on a single breeding male hence the number is reletivly small. A pack as in wolves can consist of multiple breeding pairs so the number can get quite large. Which model suits the T.rex best?

My guess is if there are millions of prey animals then it could support the wolf model, if the numbers of prey animals is smaller then the pride model suits best.

Adam Khor

Allosaur wrote: »

A pride consists on a single breeding male hence the number is reletivly small. A pack as in wolves can consist of multiple breeding pairs so the number can get quite large. Which model suits the T.rex best?

My guess is if there are millions of prey animals then it could support the wolf model, if the numbers of prey animals is smaller then the pride model suits best.

I don´t think it's that simple. You should remember several things:

- T-Rex was not a mammal, so there's absolutely no reason to assume that it had to follow one of those "models" you mention. Looking at the Harris Hawk or even crocodilians seems like a better idea IMO.

- T-Rex was MUCH bigger than lions or wolves. The food requeriments would be much greater if they were hunting as a group, so a huge amount of prey would be necessary in any case- no matter what their social structure was. If we consider the fact that plant-eating dinosaurs were becoming rather scarce and less diverse at the end of the Cretaceous, I'm thinking a large pack of T-Rex wouldn´t be viable.

- There were no prey animals in T-Rex's habitat large enough to justify coordinate hunting by a large pack. Edmontosaurus was about as large as T-Rex, and, they say, somewhat less heavy. Triceratops may have been heavier, but was still not much bigger. If you look at an adult T-Rex, it seems obvious that it was big, powerful and well armed enough to take on any of these (its two principal prey as suggested by the fossil record) on its own, or perhaps in pairs.
A large pack however wouldn´t be practical. Neither Edmontosaurus or Triceratops was large enough to provide a worthy meal for a large number of T-Rex. Many pack members would go hungry. Why waste energy and risk injury fighting with other T-Rex over a carcass, when they could go and hunt their own Edmontosaurus or Triceratops?
The only dinosaur I can think of large enough to feed a hypothetical T-Rex pack without any of them going hungry would be Alamosaurus- but it was so huge, so rare, and seemingly, so geographically restricted, that it seems unlikely to have been an important part of the T-Rex menu.

Of course, this doesn´t rule out the possibility of several T-Rex gathering at a kill site, attracted by the smell of blood and dead flesh (as they could smell prey from miles away) or the sounds made by either prey or predator (T-Rex seemingly could hear infrasounds and these sounds travel greater distances than higher frequency sounds, so T-Rex from far away could be attracted to a carcass by listening to these infrasounds). It is even possible that they could watch scavenging birds or pterosaurs circling the sky and follow them to a kill, same way as hyenas and lions do today.

Then, like Komodo dragons, the T-Rex could gather together and eat from the same carcass- with the largest, fiercest individuals dominating and eating the best parts, and the smaller, faster ones waiting for the scraps. It is even possible that, as with Komodos, the smaller ones were sometimes cannibalized by larger individuals that didn´t get to eat from the carcass.

As "lowly" as this behavior may seem compared to wolves or lions hunting together, I think it makes more sense for T-Rex.

Also, as a side note, lion prides can and often have more than one breeding male, AND wolves usually limit their own population by having only one breeding pair- not ALL the wolves in a pack breed. In fact, usually most members of the pack are directly related to the mated pair, and help raise the cubs of the breeding pair. Basically, the wolf pack is a large family.
There are no absolute rules in animal behavior, though, so it IS possible for some wolf packs to have more than one breeding pair, and is IS possible that a pack has many members- as many as 30 or 40. The same, however, is known for lions. Huge prides with several breeding males are known.