Re: Lack of Running Giant Theropod Tracks

[Don Ohmes <d_ohmes@yahoo.com>]

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...