An interesting conundrum and or theory.

Alvin T. Grey

It's got to do with the late cretatious period of North America, and or China..

The puzzle is "Where are all of the rest of the theropods..."

It seems that in the three ages of dinosaurs that there was never a single apex theropod.
For example, in the Jurassic we had Allosaurus coexisting with Ceratasaurus and Torvosaurus. In the early cretatious we had Gorgosaurus and Daspleteasaurus, Branching later into into Albertasaurus (T. Rex) and finally Tyrannosaurus Rex (T. Rex) all on it's own....

The pattern continues in Gondwanan theropods:
You had Rugops, Spinosaurus and Charcharodontosaurus (rediculous name).
Agross the then nascent Atlantic ocean you had Giganotosaurus and that new abeliosaur 'whats-his-face-o-saurus'.

But in N. America, and China you had just the Tyrannosaurs.

The question is why?

Galvasean

Don't forget South America also had the spinosaur Oxalaia and Africa also had Deltadromeus/Bahariasaurus.

Rubecula

Just because we have only found one type of fossil does not mean there was only one type of creature. There may have only been one, but equally there may have been more we have not yet found. Despite what many people think Fossils are very rare and depend on the right conditions to be formed. How many creatures have existed and how many fossils exist?

Countless trillions of creatures yet we only have fossils numbered in the thousands.

Alvin T. Grey

Understood;
However if we look at the rest of the world with the same eye (especially gondwana) we see multiple theropods coexisting back then. But the trend is not repeated in those two areas, and the common feature between the two appears to be Tyrannosaurs. (Tarby and Rex).

I'd like to look into it a little further before I post more. Mostly because I'd like to get my dating as exact - which means lots of reading of publications - as I can to determine if they actually co-existed or if "Late Cretatious" is an inaccurate time frame.

Interesting non the less I hope.

Rubecula

Oh yes don't misunderstand me. I enjoyed your post, just wanted to point out some obvious arguments. but it is interesting.

Adam Khor

Alvin T. Grey wrote: »

It's got to do with the late cretatious period of North America, and or China..

The puzzle is "Where are all of the rest of the theropods..."

It seems that in the three ages of dinosaurs that there was never a single apex theropod.
For example, in the Jurassic we had Allosaurus coexisting with Ceratasaurus and Torvosaurus. In the early cretatious we had Gorgosaurus and Daspleteasaurus, Branching later into into Albertasaurus (T. Rex) and finally Tyrannosaurus Rex (T. Rex) all on it's own....

The pattern continues in Gondwanan theropods:
You had Rugops, Spinosaurus and Charcharodontosaurus (rediculous name).
Agross the then nascent Atlantic ocean you had Giganotosaurus and that new abeliosaur 'whats-his-face-o-saurus'.

But in N. America, and China you had just the Tyrannosaurs.

The question is why?

You mean Ekrixinatosaurus, right?

I think there's no way tyrannosaurs were the only large predators around- there must have been others, perhaps living in different habitats and hunting different prey. Like Rubecula said, we only know a little fraction of the creatures that lived in any given Mesozoic habitat- for example, scientists used to believe that the Jehol biota lacked any giant dinosaurs, since only the small ones were being found, yet now we know they were present after all - with the discovery of the giant tyrannosauroid Sinotyrannus and some iguanodonts and sauropods. There were probably many that were never preserved as fossils at all.
It is possible, though, that the larger dinosaurs seem to be rare in Jehol because they prefered to live in open areas, whereas the Jehol fossils come from what used to be dense, temperate to cold forests around lakes; giant dinosaurs would need more space and so they were more abundant in open terrain.

Maybe Tyrannosaurus and Tarbosaurus were also open field creatures and the fossils we have of them and their "neighbors" come from what used to be relatively open plains? Which I think is the case, if I'm not mistaken... it makes sense considering how huge these creatures were.
Maybe it was similar to some places in Africa, where lions dominate open terrain and so smaller predators, like leopards and golden cats, despite being able to hunt and live in the savannah, prefer to live in the forest, avoiding both competition and predation by lions? Same happens in North America, where black bears often avoid grizzlies by living in more dense forests and avoiding open fields.
The fact that animals don´t fossilize as well in forests as they do in other habitats is also to be considered; we know practically nothing, for example, about prehistoric rainforests in Africa or South America; almost all fossils come from what used to be savannahs and open floodplains.
I suspect the same happens with dinosaurs; if you think about it, most known dinosaurs lived in plains or near coasts; we know very little about forest and upland dwelling dinosaurs (or pterosaurs for that matter).

Now, this is not to say that Tyrannosaurus/Tarbosaurus was the only large predator around- there may be others waiting to be discovered, or perhaps they have already been discovered but mislabelled or misidentified as belonging to already known species.
Finally, there's the possibility that maybe the latest Cretaceous habitats in these regions were not as resource-rich as they were in earlier times, and so couldn´t support a great number of different carnivores at the same time. Keep in mind that dinosaurs were much more diverse (or so it seems) a few million years before Tyrannosaurus/Tarbosaurus, then diversity starts to fade away... maybe they were, after all, endangered by the time the meteorite struck?
This makes sense if you consider that large sauropods in both latest Cretaceous North America and Asia are quite rare- this suggests, to me anyways, that there wasn´t enough food to support great numbers of them, and that hadrosaurs and ceratopsians managed because they were better adapted to process tougher, less nutritious food.
In the other prehistoric ecostysems you mention- like Allosaurus, Torvosaurus and Ceratosaurus, or Spinosaurus, Carcharodontosaurus, Rugops and Deltadromeus- there were plenty of sauropods suggesting more abundant resources...

Galvasean

Adam Khor wrote: »

In the other prehistoric ecostysems you mention- like Allosaurus, Torvosaurus and Ceratosaurus, or Spinosaurus, Carcharodontosaurus, Rugops and Deltadromeus- there were plenty of sauropods suggesting more abundant resources...

You might be on to something there. Such a lack of resources could support the theory that dinosaurs were doing rather poorly before the KT event - a sort of ecological 'weeding out' of different varieties of dinosaurs.

Alvin T. Grey

Galvasean wrote: »

You might be on to something there. Such a lack of resources could support the theory that dinosaurs were doing rather poorly before the KT event - a sort of ecological 'weeding out' of different varieties of dinosaurs.

Are we thinking that something as large as a sauropod could be the base of a food chain? - Wow:D

But it does seem to be particularly coincidental, - large sauropods in the jurassic meant multiple preditors, continuing on into the early cretatious we had well dispersed preditors and multiple varities.

Then suddenly a lack of sauropods and a consequent lack of variety among the preditors...
We also know that south of the equator we had ma-hoo-sive sauropods continuing into the cretatious....and lo and behold - multiple preditors of different families even.
Spinos, charchars, abelisours. oh my!

Tis interesting indeed..

Galvasean

Perhaps not the base of the food chain, but massive herds of animals that weigh in the high tens of tonnes represent a heck of a lot of biomass (and of course food). Even if very few carnivores were capable of hunting them what sauropods did die each would have represented a massive meat bonanza for any carnivores in the area.

Rubecula

And insects too, and they are at the base of a massive food web. A Sauropod would really be a massive source of insect protein when you come to think of it. And what would feed on them, and so on?

Adam Khor

Alvin T. Grey wrote: »

Are we thinking that something as large as a sauropod could be the base of a food chain? - Wow:D

Not at the base of the food chain- what I meant is that you need a lot of resources to feed large numbers of sauropods. The fact that sauropods became scarce in the Northern Hemisphere during the last million years of the Cretaceous suggests that there was either not enough food or suitable habitats for them.
Hadrosaurs and ceratopsians were better at processing tough vegetable matter and probably could feed on less nutritious plants, apart from the obvious fact that their food requirements were not as monstrous.

Alvin T. Grey

Adam Khor wrote: »

Not at the base of the food chain- what I meant is that you need a lot of resources to feed large numbers of sauropods. The fact that sauropods became scarce in the Northern Hemisphere during the last million years of the Cretaceous suggests that there was either not enough food or suitable habitats for them.
Hadrosaurs and ceratopsians were better at processing tough vegetable matter and probably could feed on less nutritious plants, apart from the obvious fact that their food requirements were not as monstrous.

I'm using that term loosly. (very)

Hmmmm. Could it be as simple as tieing together several theories regarding the demise of the sauropods and, yes, even the impossibility of the sauropods themselves to explain it.

1. Our favourite - Climate change.
In th north hemesphere, did it get hotter and drier. We know that the western interior seaway dried up, and that the lower (better adapted to grazing/browsing) animals seemed to flurish. - So did it go from mixed forest to savannah?

2. Deforestation - Because of the above, the higher flora wasn't as abundant. So your sauropods couldn't eat their fill of leafy goodness.

3. Food type. - Because (it's a wacky one) the size of the mouth of a sauropod is so small compared to the rest of it's body, it needed to get the good stuff in order to get enough through the mouth to feed such a bulk. - Essentially I call this the 'McDonalds Theory'. the food quality remaining wasn't good enough with the volumes available through its mouth in a 24 hours period to keep it going.

Adam Khor

Alvin T. Grey wrote: »

In th north hemesphere, did it get hotter and drier.

Actually I remember reading somewhere that the Cretaceous was actually cooler (as in, lower temperatures XD) than the Jurassic, particularly during the last million years...

But Im not sure if this info is outdated.

Alvin T. Grey

Adam Khor wrote: »

Actually I remember reading somewhere that the Cretaceous was actually cooler (as in, lower temperatures XD) than the Jurassic, particularly during the last million years...

But Im not sure if this info is outdated.

You're right. Brainfade here....
It got cooler and drier.