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Re: Lack of Running Giant Theropod Tracks



On 11/28/2010 12:10 PM, Sim Koning wrote:
Most if not all ornithopods could probably run and ceratopsids may have been 
able to gallop, which means giant theropods would have needed to run to catch 
them.
> I have a hard time believing that giant theropods such as tyrannosaurs would have limited their prey to the largest and most powerful animals in their ecosystem.

Which were what? Surely you don't mean sauropods? A Boy Scout with a piece of rope and a sharp knife could kill the biggest sauropod that ever lived. In relative safety, at that.

So if there was a drop off in speed (loss of the ability to run) when a 
carnosaurs/tyrannosaurs reached giant sizes, I'm left wondering why having your 
prey options limited to the most dangerous herbivores in your ecosystem would 
have been an advantage.

Again, I assume you mean sauropods. I am flabbergasted every time this comes up on list, and I mean nothing personal in this. Everybody seems to agree w/ you, but can offer nothing to defend this intuition become an institution.

Try a thought experiment -- drop down on all fours and become a sauropod. Your neck is now as long as your torso, and as big around as your finger, or maybe something a little more sensitive. How big is your head? Really, really, small...

On ground where it's mobility is not impaired, any small and aggressive dog could kill you easily with one bite should it be able to teach your neck, even at the base.

Predators do not need to eat very often, and extremely large herbivores do. How long do you think you can "rear up and thrash your tail"? Who gets tired first? Are there trees or rocks? Well, then forget about doing any tail-thrashing...

I do not accept that the general pattern seen in the geo-record is a coincidence -- that is, the largest sauropod is matched by a large-jawed meateater just about exactly tall enough to reach the base of the throat at any given moment. IMO, sauropods got big because once their lifestyle was set, they had to be taller than the mega-theropod of the day. They had to get those long skinny necks as far off the ground as possible.

Juveniles of prey species are often a primary target for predation and at least 
the juvenile ceratopsids were probably capable of rhino like speeds. I imagine 
that if Tyrannosaurs were limited to 10 to 15 mph they would have effectively 
been prevented from catching the juveniles of their primary prey. Of course 
this could be why juvenile tyrannosaurs were more gracile, but having a lighter 
build and more blade like teeth wouldn't have helped much in bringing down the 
juveniles of animals such as Triceratops.

In my opinion, Trikes were the most dangerous to T. rex, on level ground and good footing. A frontal attack was near-suicide. A herd may have been extremely aggressive and also faster. An elderly trike w/ resorbed horns that was cast-out of the herd would certainly be an exception, though.

I'm guessing the more gracile build of juvenile Tyrannosaurs may gave been an adaptation 
to allow them to catch species (such as ornithomimids) that were almost completely out of 
"range" for the giant adults; a similar relationsip can be seen between lions 
and cheetahs.
If I'm not mistaken, most if not all predators alive today are capable of 
running down and killing most of the smaller animals in their environment. As 
an example, lions can be seen killing everything from gazelles to young 
elephants and so are not limited to a few dangerous prey species. However, I am 
aware that this is one big argument from analogy, and the analogy may not be a 
very good one.

Imagine how easy an elephant would to kill if all you had to do was bite the end of it's trunk. Think about it.

Tactically speaking -- a sauropod in a parking lot would be easy meat to a persistent giant theropod.

Verso -- a theropod in a swamp or even on muddy ground could not safely approach a large sauropod. "You have fallen, and are now flat as a fritter." says the big guy w/ the skinny neck.

As to T. rex -- have you thought about this? The scarcity of sauropods in the sediments where T. rex is found may be due to T. rex's extreme proficiency as a hunter, and a climate that ensured that almost all sauropods would periodically have to leave swampy refuges in search of muddier pastures? Bones on the hill are rarely preserved.

Lastly, but most importantly -- how do you answer the work of JR Hutchison and others, which sums to "not possible"?

Googling "AMNH theropod problem" brings up the "too big to run" case. It is convincing...