Re: Jobaria and the Elephant Commit Suicide

["Matthew Bonnan" <mbonnan@hotmail.com>]

Richard Travsky writes (in response to my which elephant? question):
> The jobaria web page specifies Sereno had access to a 20 year old African
> elephant named Angus.

Yes, I am aware of this.  I don't think I stated my point clearly.  The 
point is, which elephant behavior are you going to use, and why use that one 
particular elephant over another.  While I am no elephant expert, do we know 
how often certain elephants rear, how their behaviors differ, etc.?  We are 
only using an analog for potential sauropod rearing, and we must be careful 
not to extend these behaviors  to sauropods.

I am well aware they weighed this elephant, front and back, and found a 
"reversed" condition of weight bearing in Jobaria.  While it was great that 
we have the live weight of an elephant on record (most elephant weights come 
from carcasses), the observation that Jobaria has smaller hands than feet, 
the reverse of an elephant, is nothing new.  I'm sure they included it to 
emphasize their point, but this in and of itself does not tell us that these 
guys were rearing up.  If sauropods are descendants of bipedal relatives, 
this difference in hand vs. foot size could merely be a relict of their 
former bipedal natures.

I wonder how they calculated the femur's weight-bearing capacity?  Sure, you 
have circumference, cross-sectional measures, etc., but how they arrived at 
3 times the weight of the animal would be interesting to know.  But let's 
say this is true.  Is this "overbuilt" as has been suggested?  Well, all 
animals have bones with safety factors, in some the safety factor can get up 
to 5 times the weight.  3 times falls within the range we see reported for 
elephants (Knut-Schmidt Nielsen, 1984, Size) so I'm not too sure the 
condition in Jobaria would be overbuilt ... unless they meant three times as 
much as an elephant -- that's a little different.

Still, let's go with the 3 times idea.  When animals move their limbs, they 
increase the loads on them dramatically, even when just walking.  From 
memory without a reference in front of my face, a human walking moderately 
fast can nearly double the normal weight going through their limbs.  
Something as large and heavy as Jobaria certainly would have greatly 
increased the force through its limb bones just walking to be sure.  Now 
take that weight and spread it out on only the hindlimbs ... not saying this 
was impossible, but just something to consider.

Here's something else to think about.  Maybe the bones can support 3 times 
the weight in COMPRESSION (i.e., when they are vertical), but less (I would 
expect) if they are bent.  Sereno et al. give us restorations of the 
elephant and sauropod with BENT knees while rearing (and actually, all the 
restorations I have seen of Jobaria and other sauropods restored by Sereno 
et al have bent knees while walking).  What effect does such a position have 
on the femur?  What torques are produced?  Should the femur bend, as it does 
in an elephant, for a sauropod to rear or is this a case of the analog 
leading the functional interpretation?  See what I mean about the analogs 
being a slippery slope?

I again emphasize the Caudofemoralis longus tail muscle.  Elephants have no 
real tail to speak of, yet the tail of sauropods had muscles which were 
intimately tied with locomotion.  How are these tail/femur muscles being 
accounted for?  If you bend your knees so that the femur swings forward, how 
far can that muscle stretch?  Would such a muscle restrict how far you can 
rear up?  At this point, I am not satisfied with current sauropod rearing 
explanations.

Richard further adds:
> If a threat display deters a predator(s),then this is a cheap means of
> survival. A lot cheaper than incurring wounds.

Seems like an awful waste of energy.  Allosaurus and Ceratosaurs aren't all 
that big -- a sauropod is still a pretty huge animal to them.  Do elephants 
rear to scare away predators?  Are we sure that no rearing incurs wounds 
from predators?

Further:
> Which would make it effective in defense. (Think of the noise alone!)

Yikes!  When I said the crashing down of a sauropod gives me the willies, I 
meant that it stands an awful risk of breaking its bones, not the noise. =)  
Remember those weight safety factors?  Imagine you are a gigantic animal 
that is pretty heavy and relies on all fours to get around.  Would such an 
animal engage in activies that would push its limb bones to the extremes of 
their safety factors?  Break a bone in your forelimb, now what?

If you rear up, how do you look down at your attacker?  No matter how the 
neck goes together, that little head is way up there, maybe trying to look 
down with one or the other eye in its skull.  But let's say you can.  So now 
you're up on your hindlimbs stuck in place.  You can't pivot because your 
femora have cylindrical heads and you have stiff-action ankles.  And you 
can't use your tail because its on the ground as a tripodal support.

I insist we have to be careful and do more rigorous work on sauropods.  
Analogs are EXTREMELY tricky and we must use them with caution.

Matt Bonnan

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