Re: Hadrosaurs outgrew tyrannosaurs

[dinoboygraphics@aol.com]

I think the emphasis is on individual reproductive fitness.  From a 
selective point of view reducing the time your offspring has to spend 
in a more vulnerable size range reduces the odds of it not surviving to 
reproduce itself.  Of course as HP Holtz has already mentioned 
hadrosaurs inherited the condition from their ancestors, so the real 
question is why did tyrannosaurs prolong their growth trajectory (or 
indeed, where did the trend first begin?).

Just speculating, but here's a totally non predator-prey explanation 
for the growth rate of tyrannosaurs:

We know that basally dinosaurs grew fast, and that gigantism seems more 
often than not to have come by increasing growth rates (rather than the 
traditional diapsid solution of extending the growth period while 
retaining the ancestral growth rate).  We also know that the size 
reduction seen in stem-birds seems to have resulted in reducing growth 
rates rather than dramatically shortening the growth period.  Finallly, 
we know that this happened in the Early Cretaceous.

Tyrannosaur relatives at the time are small, and may be reasonably 
assumed to have utilized lower growth rates relative to the basal 
tetanuran condition to assume that size range.  So...what if in the 50+ 
million years between that stage and the eventual gigantism of 
end-cretaceous tyrannosaurs the linneage canalized the growth rate, 
making gigantism only (or at least primarily) achievable via 
lengthening the growth period.

This speculation generates several testable hypotheses:

1) Indentified basal tyannosaurs with small body (e.g. Dilong) size 
should have a growth rate similar to Late K tyrannosaurs (and lower 
than the basal tentanuran rate).

2) Initial size increases (e.g. Alioramus, aublysodonts) should show an 
increase in growth period rather than an incease in size.

If either proves to be false then we can rule out the idea of a 
canalized growth rate.  Also, if initial size increases in the 
tyrannosaur linneage do show a growth rate increase (followed by a 
subsequent decrease in end K tyrannosaurs) then we probably need to 
invoke some environmental selective factor (including P/P interactions) 
and/or a population dynamics constraint (can only fit so many adult 
tyrannosaurs into the western US and Asia).

Just food for thought...

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message-----
From: john hunt <john.bass@ntlworld.com>
To: xrciseguy@q.com; 'Dinosaur Mailing List' <dinosaur@usc.edu>
Sent: Thu, 7 Aug 2008 11:31 am
Subject: RE: Hadrosaurs outgrew tyrannosaurs



While this is all good stuff on growth rates I don't really understand 
why
such significance is placed on hadrosaurs outgrowing tyrannosaurs.  
There
were always going to be younger hadrosaurs smaller then the 
tyrannosaurs -
its not like they were only allowed to eats dinosaurs the same age ;-)

-----Original Message-----
From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf 
Of
GUY LEAHY
Sent: 07 August 2008 01:36
To: Dinosaur Mailing List
Subject: Hadrosaurs outgrew tyrannosaurs


Interesting work!  Here is the press release:

http://news.research.ohiou.edu/news/index.php?item=501

And the full paper:

http://journals.royalsociety.org/content/t68465274748300k/fulltext.pdf

Guy Leahy