Re: Chicago Tribune article about Jane the juvenile T. rex exhibit at the Burpee Museum

[Sarah Werning <swerning@gmail.com>]

If they used the same element used to estimate Sue's age (Erickson,
2004), it would have been the fibula.

In answer to the question from your previous email ("Why doesn't the
tibia bone in dinosaurs get remodeled with increasing age?"), the
tibia does get remodelled with age, but apparently in some dinos, the
fibula does not. In most long bones, the older LAGs/rings (the ones
closer to the center of the bone) are lost when the bone is remodelled
and also as the medullary cavity expands. The fibula has the advantage
of no medullary cavity, so in tyrannosaurs (which do not remodel their
fibulae), one can count the earlier rings that are lost to the
expanding medullary cavity and remodelling that happens in the larger
long bones like the femur and tibia, making it a good choice for age
determination (It also has the practical advantage of a much smaller
diameter, which means you can fit the whole cross section on one
slide!).

It is worth mentioning that in other dinosaurs (such as Tenontosaurus,
the ornithopod whose bone histology and growth I'm looking at for my
MS thesis), the fibula undergoes early, extensive remodelling and is
completely useless for determining age by LAG counts. For Tenonto's,
the best bone for estimating age by number of LAGs is the tibia, but
because of the reasons mentioned above, you have to do a bit of
back-calculation to arrive at the animal's approximate age at death.
Another complication is that different elements will have different
numbers of LAGs (as in Maiasaura - see Horner et al, 2000). In
Tenontosaurus, the tibia consistently has the highest number of LAGs
of all the long bones, and the femur will usually have the same, one
or two fewer LAGs. I do not know how much the number of LAGs varies by
element in theropods, though.

Hope this helps,
Sarah


Sarah Werning
Graduate Student, Department of Zoology
University of Oklahoma
730 Van Vleet Oval, Room 314
Norman, OK   73019
swerning@ou.edu


On 6/28/05, Phil Bigelow <bigelowp@juno.com> wrote:
> 
> I think I meant to write "fibula".
> 
> <pb>
> 
> On Tue, 28 Jun 2005 09:41:53 +0000 (pd) Phil Bigelow <bigelowp@juno.com>
> writes:
> 
> > That [analysis of growth rings] would probably be on the tibia, right?
> BTW:  Why doesn't the
> > tibia
> > bone in dinosaurs get remodeled with increasing age?
> >
> >
> > <pb>
> > --
> >
> >
> >
> >
> >
> 
> 
>