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Re: Stego/Ankylo limbs (long)



>        Certainly the elbows of a Triceratops are strongly built structures
>-- the animal was obviously built for charging -- but what reinforcements do
>you see for lateral stresses produced from a sprawling posture?

In a sprawling posture, the humerus would be protected by the ulna, as the ulna
wraps around the humerus slightly.  This would take care of any additional
stresses.

>        As  Nicholas Pharris pointed out, the front limbs on a horse are not
>straight but slightly flexed at the backwardly pointing elbows.  The reason
>for this is very important.  As the animal walks or runs the leg is first
>extended as the horse reaches out in front of itself, then flexes primarily
>at the elbow, storing energy like a spring, and then extends, releasing the
>energy and propelling the animal forward.  This entire process occurs in the
>vertical plane containing the motion vector of the animal.

Again, the result of this would be a very sore T-tops.  See previous post.
  
>        In your sprawling Triceratops, as the leg is extended, the energy
>stored will be released in force vector NOT lying in the plane described
>above, but rather askew, propelling the animal sideways as well as forwards.
>This is not only an obviously inefficient mode of locomotion, but jarring to
>all the joints in the forelimbs, since the opposite front limb must stop the
>lateral motion.

This is not a problem since the primary force for propultion would come from the
hind legs.  The front limbs wouldn't have to do much more than steer.  So they 
wouldn't have to be efficent in locomotion.
 
>        Additionally the wrists would not only have to absorb the punishment
>I describe above, but would be under much stress as the forearm would both
>pivot and twist under the range of motion necessary for your sprawling model.

The bones in question are sufficently large enough to handle the excess load.
  
>        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.

>You state in another reply:
>       
>> When they migrate to North America, the "dune buggy" design, which 
>> gives them an immense  stability (definately an advantage) on the "stable" 
>>  land surface, which helps them to be an extremely successful group.  
>> This success is marked by an increase in size.
>> ... 
>> Take a look at a dune buggy sometime.  The similarity in forms between
>> the ceratopian forlimb system and a dune buggy front axle assembly are
>> remarkably the same.
>
>        You definitely need to elaborate on your "dune buggy" analogy.  You
>have already discounted the wide-gauge "stance" of a dune buggy, by
>acknowledging ceratopian trackways showing that the forelimbs are no further
>apart than the hind limbs.

A feature found in most dune buggy tracks.

  The only other similarity I can see (correct me
>if I wrong -- I'm no dune buggy expert) is that the front tires slant away
>from the car slightly, giving a visual appearance similar to a sprawling
>Triceratop's forearms, but the reason the tires slant outward is to allow a
>lot of vertical play in the wheels as the car  rolls over irregular surfaces.

Exactly the reason why ceratopians evolved a similar form.  The dunes of the
Gobi are about as irregular as one can get.

>        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.

>        One thing is almost certain: ceratopians were very good walkers
>(from evidence of vast migrations).  They were probably also decent runners
>(chargers) judging from their armaments and coeval similarities with modern
>rhinos.  Of all of the major physical characteristics of such highly
>successful migratory animals, limb structure would have to be refined and
>efficient.  For such a large, mobile and quite possibly agile collection of
>creatures, the forelimb structure that you describe is primitive,
>inefficient, and ill suited for them.

I'm afraid I can't agree.  As I see it, the sprawling forelimb is a fantastic
(although unique) adaption among dinosaurs.  The immense stability brought on 
by this form would be a tremendous advantage.  For example, it wouldn't have to 
slow down while making a turn; excellent in predator evasion.

Rob

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

A.  The antiarch.