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Re: Stego/Ankylo limbs (long)



>> hind legs.  The front limbs wouldn't have to do much more than steer.  
>> So they wouldn't have to be efficent in locomotion.
>
>Wrong.  Unless the front legs have some sort of wheels or runners on 
>them, they need to be just as efficient in locomotion as the hind legs, 
>or at least be able to keep up.

However, since the main thrust is being provided by the hindlegs, the forelegs
can afford to lose a little efficency for the sake of stability.  A decent
trade-off in my book.

>> >        Finally, the reinforcements you mention in the shoulder are
>> >consistent with a large charging animal that would have to change course
>> >quickly or lunge sideways.
>> 
>> However, the reinforcements I mentioned only match up (and therefore, only
>> apply) if the humerus is held horizontal to the shoulder articulation.
>
>I fail to see how that is true.

The feature I point out is the reinforcement process located on the upper
humerus, which lines up with a similar process on the scapulacoricoid.  These
two processes match up only when the humerus is held horizontally out from the
shoulder attachment.

>> Exactly the reason why ceratopians evolved a similar form.  The dunes of the
>> Gobi are about as irregular as one can get.
>
>Yes, but the best way for an animal, which has legs, not wheels, to deal 
>with surface irregularity is to develop long legs which can step *over* 
>any irregularity.

That is certainly one way of dealing with it.  I say that ceratopians simply
evolved a separate and unique solution.  Also, since dune irregularity is
changing constantly, the best way to deal with it, is to develop a squat form.

>> >        By sprawling, not only are you moving the Triceratops closer to the
>> >ground, but you are placing more weight on the forelimbs making them sink
>> >even deeper into the sand.  You are not suggesting "dune surfing" are you?
>> 
>> Actually, by holding the feet out to the side, it spreads the total weight of
>> the animal over a wide area.  This would reduce the total load on the 
>> forefeet.
>
>No, it does not.  The weight of the animal is distributed over the area 
>of the parts of its feet in contact with the ground.  No more; no less.  If 
>the animal slopes down sharply towards the forelimbs, these must bear a large 
>portion of the animal's total weight, and, as mentioned above, the animal 
>sinks into the sand.

Sorry, your wrong on this one.  Set this one up as a physics problem regarding
the justification of stresses (I can't think of the real term, but this is close
enough).  With the feet under the body, the stress diagram looks like this:

         1
         1 w
         1
         V

In this case, the force on the feet (w) equals the mass times the acceleration 
due to gravity (simple Newtonian stuff).

With the forelimb held off to the side, the diagram looks like this:

        --------->1
         \ A      1
          \       1
           \      1
            \     1 x
          H  \    1
              \   1
               \  1
                \ 1
                 >V

Where:
        H = Hypotenus (with a value equal to w).

        A = The angle between hypotenuse and horizontal.

        X = Total load applied to the feet.

Trigonometry says that X = H.cos A.  Since the cosine of any angle (provided
A < 90) is always less than one, then X < H.  Therefore, the total load applied
to the feet is less with the feet held out to the side.

Rob

***
Q.  What fossil fish is a blood relative?

A.  The antiarch.