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RE: Lack of Running Giant Theropod Tracks

> Because with the growth curve drawn by Erickson (?), selective
> pressure must be very strong for the long time T rex juveniles have a
> mass of below 1-2 tons. Thus selective pressure may be different from
> extant animals.
  This is made all the more likely by the possibility that specimens such as 
Jane were in fact juveniles of T. rex. A pair of adult T. rex were probably 
strong and fast enough to hunt and kill most of the animals in their ecosystem, 
which would have made for some pretty stiff competition for the juveniles. The 
rather short lifespan of the adults would have meant that there would have been 
groups of "orphaned" juveniles even if there had been extensive parental care. 
With a top speed of around 25 mph, the adults were probably too slow to hunt 
ornithomimids and juvenile hadrosaurs, which would have left a niche open for 
the juveniles to exploit. The elongated jaws and longer forelimbs of the 
juveniles would have been useful in gripping or tripping up fast moving 
ornithomimids. If siblings remained together in a pack, they may have been able 
to use their blade like teeth to disembowel larger hadrosaurs; working together 
would have also allowed juveniles to consume their prey as quickly as possible 
before it was stolen by the adults. If the adults were cannibalistic, being 
able to outrun them would have been extremely useful.
  Adult tyrannosaurs, although slower, would have been able to kill ceratopsids 
and ankylosaurs, animals that the juveniles may have been too weak and 
blade-toothed to exploit. However, making a living by attacking something that 
is not only your own size, but also able to kill you as easily as you could 
kill it, may not have made for a very survivable lifestyle. One possible way to 
compensate for the extreme risk inherent in attacking such animals would have 
been to work in mated pairs. As any trained fighter will tell you, your chances 
of winning a fight drops dramatically when facing more than one opponent. If a 
pair of Tyrannosaurs isolated a Triceraptops, it could have only directed its 
horns at one Tyrannosaur at a time. If the robust morph was in fact female, it 
could have done the bulk of the fighting by employing such strategies as 
gripping the horns while the lighter and faster male attacked the limbs, flanks 
and neck. The fact that we have a Triceratops with a horn bitten off makes such 
a scenario more plausible. Working together in pairs, rather than packs, may 
have been an effective way to minimize risk while ensuring that there was 
enough food to available per kill for the adults and their young. Solitary 
adults may have been fast enough to prey upon hardrosaurs, juvenile 
Triceratops, small ornithopods, pachycephalosaurs etc. but not fast enough to 
to hunt ornithomimids, or young hadrosaurs, and they may not have been able to 
turn and pivot fast enough to safely outmaneuver an adult Tricerators.
 I think there is something else to consider as well: if the juveniles were 
very well adapted for running, then there is no reason to think those same 
adaptations were lost upon reaching maturity. I think this, along with the 
research on the caudofemoralis supports the higher end estimates (between 20 
and 30 mph) for adult Tyrannosaurs. So in this regard I agree with Greg Paul in 
that these animals were scaled up versions of running animals and look fast 
because they were (for their size) fast. On the other hand, the fact that the 
work of Hutchinson et al strongly suggests that top speed heavily declined once 
certain sizes were reached may help explain the extreme differences between 
adult and juvenile morphology.
Simeon Koning                     

> Date: Wed, 1 Dec 2010 09:26:12 +0100
> From: martin.baeker@tu-bs.de
> To: mike@indexdata.com
> CC: erikboehm07@yahoo.com; dannj@alphalink.com.au; dinosaur@usc.edu; 
> hmwh@comcast.net
> Subject: Re: Lack of Running Giant Theropod Tracks
> > Plausible, yes. But I'm still interested in the question I asked a
> > day or two ago: does anyone know ANY extant tetrapod in which the
> > juveniles can run faster than the adults? I can't think of any --
> > which of course doesn't mean there aren't any, hence the question.
> >
> I think the following question is strongly related: Is there any
> extant animal (apart, perhaps, from humans) that needs more than 15
> years to reach full size and has a life expectancy of only 30 years?
> Because with the growth curve drawn by Erickson (?), selective
> pressure must be very strong for the long time T rex juveniles have a
> mass of below 1-2 tons. Thus selective pressure may be different from
> extant animals.
> Priv.-Doz. Dr. Martin Bäker
> Institut für Werkstoffe
> Technische Universität Braunschweig
> Langer Kamp 8
> 38106 Braunschweig
> Germany
> Tel.: 00-49-531-391-3073
> Fax 00-49-531-391-3058
> e-mail