RE: More about Erickson et al. 2004 and RE: Delayed "growth spurt" in T. rex

["Jonathan R. Wagner" <jonathan.r.wagner@mail.utexas.edu>]

To throw in my two cents: the "twisted"  (grab the middle of the curve and 
turn counter-clockwise) growth curves of tyrannosaurs make sense both for a 
small-pack scenario and tyrannosaurs as loners.

In the former case, it might be advantageous for a family-group pack 
(pride?) to maintain a small stock of smaller juveniles, either to assist 
in hunting (if that is what they did), or simply to ensure that a few of 
them survived "training." With one or more large adults already present, 
smaller juveniles means less food expended on them, which means fewer kills 
are necessary (less danger, good thing). The need for more food that 
probably coincided with the steeper portion of the growth trajectory might 
then have coincided with an increased appetite (as it seems to in humans 
:), monopolization of pack resources by the teenager, and might have 
triggered expulsion from the pack. This, of course, NEVER happens in human 
families... ;)

However, as others have noted, sigmoidal growth curves are the rule, rather 
than the exception. Rapid growth may simply have been a way to rapidly 
traverse the size gap between the "small" predator niche (1 ton... recall 
the gap between small and large predators in Late K northern Great Plains 
faunas), and that of the largest predators. If tyrannosaurs were 
territorial, particularly abundant, or simply hungry, they might 
preferrentially eliminate the competition while it is younger and smaller, 
but just beginning to compete for the same resources (large herbivores), 
rather than wait until it hits full size. It is possible that such rapid 
growth to great height necessitates a long lead time; that makes sense 
graphically, but I'm not sure what the biological reason would be.

As for why there aren't any really old tyrannosaurs, I very much liked the 
point about r-strategy in tyrannosaurs. We should remember that these 
animals are not large mammalian HERBIVORES, they are top predators. That is 
a very rough life, with angry prey, other large predators, disease, 
tripping and killing yourself, etc. If there truly wasn't much selection 
for long life, there certainly would have been a large number of potential 
means to shorten it!

Not that this is anything new, I just felt the need to pipe up. After all, 
this IS the Theropod Mailing List!

:)

Wagner

P.S. Don't forget to cc me in replies!