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Re:Tyrannosaurid Growth Spurts



Adam Britton discussed the use of LAGs in assessing ages and the problems
associated using these. Whereas times of stress can delay laying down
LAGs, the authors of the study DID regard the resporption issue with
regards to medullary long bones, but assessing other bones that were
determined to lack remodelling, and thus preserved their entire layering
history:

  "Finally, preliminary analyses for this research revealed that several
non-weight-bearing bones in tyrannosaurids (for example pubes, fibulae,
ribs, gastralia and postorbitals) did not develop hollow medullar cavities
and showed negligible intracortical remodelling during their entire life
history (Fig. 1)." [pg. 773]

  and

  "Methods

Assessments of tyrannosaurid longevity

Growth lines have been shown to form throughout the cranial and
post-cranial skeletons of living tetrapods16,21,22,27 and their annual
formative rhythms have been shown in lepidosaurian and archosaurian (that
is crocodilian) outgroups to dinosaurs21,22,27. This indicates that
similar annual genesis might have occurred in non-avian dinosaurs such as
tyrannosaurids3. Here we used fibulae, pubes, gastralia, ribs and cranial
bones and a few selected long-bone elements in which medullar cavity
expansion and remodelling was not pervasive. Bones such as these have been
shown to have excellent efficacy for assessing longevity in snakes21 and
lizards22, and our own multi-element histological studies on lizards and
crocodilians of known ages from the Florida Museum of Natural History,
Gainesville, and the Florida Fish and Wildlife Conservation Commission,
Gainesville, confirm this (Fig. 1). In cases where some of the
earliest-forming tyrannosaur growth rings were remodelled, losses were
accounted for by examining younger individuals in which the rings were
still present or through back-calculation methods3. Inter-elemental
comparisons revealed longevity estimates to within 1 year in all cases,
the higher values of which were used in the longevity assessments."

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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