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Re: Rex Fall part 2



From: Wayne Anderson <wander@hooked.net>
Subject: Re: Rex Fall part 2

Betty Cunningham wrote:

>Jeffrey Martz wrote:
>
>>      How exactly do broken tibias relate to the risks of a T.rex falling
>> anyhow?  Is it being  assumed for some reason that they were broken in
>> falls?
>
>I think it is assumed that if they have a broken leg, then they probably
>fell down at least once when they got it or soon after.  Yet there are
>signs of healing indicating this Farlow-death-by-falling didn't happen. 
>Of course we have no idea if the T rex was at speed when it broke it's
>leg.....
>
>-Betty

I think this is based on my comment, guessing that Sue probably
experienced a fall when the leg broke. Since the fibula seems far less
important for load- bearing than the (unbroken) tibia, I can see that
she may not have fallen, but I also think it's still likely that she
did -- from whatever broke the bone in the first place.
        Broken tibias come in because the tibia is the main
load-bearing bone in the lower leg, and a broken tibia would almost
certainly involve a fall.  I was wondering if there are any healed
broken tibias in captivity, which would be almost proof of surviving a
fall.
        As far as the speed the Rex was traveling when he/she
hypothetically falls, I don't see that it makes much
difference. Unless the animal actually slides and crashes into
something like a tree or a big rock, the only damage a horizontal
component should cause is what motorcyclists call "road rash". I
suspect that scaly skin would have a relatively low surface friction,
and high abrasion resistance, resulting in not even much of that.
        The vertical component of the fall is what causes the 6g
impact on the torso, and 14g on the head -- if we accept Farlow's
figures unmodified.
        Unless I misunderstand Farlow, speed comes into the picture in
causing the probability of a fall, not the consequences...

        By the way, wouldn't a simple "drop" fall result in the torso
weight landing directly on the pubis? This leads to three
possibilties:
        1) The pubis, acting as a vertical load-bearing column, is
able to withstand the impact (highly questionable), transferring it to
the rest of the pelvis.  The pelvis being attached to the vertebrae
can absorb most of the shock in vertebral flexion -- that is, the
dino's body would bend.
        2) The pubis breaks. Are there any known pubic bones that
exhibit a break like this, either healed or unhealed? (This seems like
a likely candidate for pseudoarthrosis, assuming initial survival.)
        3) A lack of any such evidence might be taken as indicating
that PERHAPS the dinos took some form of rolling action, probably
sideward, to avoid direct falls.

        Comments? Rebuttals?

        Wayne Anderson