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RE: Tyrannosaur growth and babies

> -----Original Message-----
> From: Thomas R. Holtz, Jr. [SMTP:th81@umail.umd.edu]
> Sent: Tuesday, December 08, 1998 8:21 AM
> To:   dinosaur@usc.edu
> Cc:   Dwight.Stewart@VLSI.com; Kari_Baker@ndsu.nodak.edu;
> brandonc@advant.com
> Subject:      Tyrannosaur growth and babies
> Several different answers to recent tyrant dino posts:
> Dwight Stewart writes:
> >     if Tyrannosaurs (& perhaps other dinosaurs) grew throughout their
> >life, do we know what the
> >     growth rate was after reaching "maturity".  The analogy I'm thinking
> >of here is crocodiles.  If memory serves, the largest salt water
> crocodile
> >ever recorded was well over 20 feet & almost a ton.  
> >     Of course, with crocodiles, the growth rate slows considerably after
> >a certain age, but it never
> >     stops.  So, how much larger could a 30 year old Tyrannosaurus rex be
> >than, say a 10 year
> >     old T. rex?
> Yep, damn good question.
> Oh, you were looking for an *answer*!  Unfortunately, we don't know at
> present.  Most evidence for most groups of dinosaurs suggest that growth
> rates drop off dramatically at some point (by analogy with modern animals,
> at or near sexual maturity), but that growth did continue.
> The problem (well, one of the problems) is getting life age dates for
> dinosaur specimens.  The idea that growth rings (LAGs, lines of arrested
> growth) can be counted like tree rings doesn't pan out, as recent studies
> by
> DeRicqles, Padian, Horner, and others show that different bones in the
> body
> of the same individual have different numbers of growth rings!
> Kristy Currie presented a paper at SVP concerning growth rates of
> _Apatosaurus_, showing (from three different lines of evidence) that it
> probably only required 10 years to reach sexual maturity, but did not
> investigate (or at least present) work on data post this age.
> So, like a lot of things about dinosaurs, we still don't know at present.

        Thanks.  This made me think of  another question. :-)  How strong is
the evidence for dimorphism in
        Tyrannosaurus rex?  What brought this to mind was a conversation I
recently had with a friend
        regarding this subject.  That made me return to Dr. Horner's The
Complete T. rex to see what it had
        to say regarding potential dimorphism.  The book indicated that Dr.
Bakker isn't sold on dimorphism
        & (in fact) believes that the more robust specimens represent a
different species.  If the only differences are size and bulk, then the
different species hypothesis doesn't seem likely to me.
        As an admittedly remote example, extant species vary more within
themselves that the total
        variation among known Tyrannosaurus specimens.