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RE: Lack of Running Giant Theropod Tracks

>All this begs the question, as Holtz implies -- why would a giant >theropod 
>species need to run?
  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. 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. 
  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. 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.
Simeon Koning  
> Date: Sun, 28 Nov 2010 09:34:31 -0500
> From: d_ohmes@yahoo.com
> To: dinosaur@usc.edu
> Subject: Re: Lack of Running Giant Theropod Tracks
> It can logically be assumed that small theropods ran, and in fact there
> examples of running tracks preserved.
> Relative to a given body-style, as size increases, the frequency and
> relative speed of running generally decreases.
> Huh, et al., in Cretaceous Research Volume 27, Issue 1, February 2006,
> Pages 123-138, present evidence that "small" (<2m hip height)
> individuals were "trotting" and "large" (2.6m maximum hip height)
> individuals were "walking" (according to the abstract). [I note in that
> the abstract, they do not make any specific claims relative to size
> scaling.]
> All this begs the question, as Holtz implies -- why would a giant
> theropod species need to run?
> That said -- maximum gait data from (e.g.) roadrunners, wild turkeys and
> ostriches could generate a curve that correlates stride frequency and
> length with size, and be combined with the data from Huh, et al., to
> provide yet another basis to 'guess-timate' the gait of the giant theropods.