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Re: Lack of Running Giant Theropod Tracks



LOTS and lots to reply to on this thread.  I will try to be brief.

Sim Koning wrote:
> Juveniles of prey species are often a primary target for predation and at 
> least the
> juvenile ceratopsids were probably capable of rhino like speeds.

Do we know of any extant animals in which the juveniles can run faster
than the adults?  While no doubt there must be a way exceptions (sea
squirts? :-)), I think they ARE exceptions.  I'm not convinced by the
widespread a priori assumption that adult ceratopsians and
tyrannosaurs were slower than the juveniles.

Don Ohmes wrote:
>> 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.

I'm not getting into the bit of the argument; I'll just state for the
record that I think Don in GROSSLY overstating the vulnerability of
sauropods, and move on.

Mike Habib wrote:
> Furthermore, given the current data on life histories in sauropods, it 
> appears that
> juvenile mortality was very high (many eggs, few adults), but adult mortality 
> appears
> low (old individuals relatively common among adults).

Actually, not so much as you might think.  Many, probably most, large
sauropod specimens are from sub-adult individuals.  For example, both
the mounted Giraffatitan in Berlin and the similar-sized Brachiosaurus
holotype on which the Chicago mount is largely based were subadult, as
evidence by the unfused scapulae and coracoids.  (We know that
scapulocoracoids did fuse in brachiosaurs from the "Ultrasaurus" scap
BYU 9462.)  If I try to think of unquestionably old sauropod
specimens, the only one that springs to mind is the "Cathetosaurus"
holotype.

Don Ohmes wrote:
> Actually, didn't the allosaurids and the sauropods disappear for N America
> at approximately the same time?

It's hard to tell.  If you mean "at the end of the Jurassic", then
there's no data: Earliest Cretaceous rocks don't conformably overlie
sauropod- and allosaur-bearing rocks anywhere in North America.  If
you mean mid-Cretaceous, then maybe -- Sauroposeidon and
Acrocanthosaurus were contemporaneous, but again we don't really have
enough rock from that time to figure out what happened and in what
order.

Finally, Martin Bäker wrote:
> (But having a 6-ton theropod run at you at 25mph would probably
> convince you that this is not really slow...)

A BIG amen to this.  According to Wikipedia, Usain Bolt's absurdly
fast 9.58 seconds for the 100 meters comes out at 23.35 mph, so even
John Hutchinson's "slow" T. rex would have been comfortably fast
enough to catch the fastest human that's ever lived on a straight,
flat track.