Re: [RE: [Re: Sauropod Trunks]]

[archosaur@usa.net]

Dwight.Stewart@VLSI.com wrote:
> 

> 

> > -----Original Message-----

>       ############################################

> 

>       Posture aside (which is very giraffe like in Brachiosaurs), the

> ability to pump blood to any height

>       is determined by cardiovascular constraints.  In modern reptiles,

> the height is constrained to just a few 

>       feet above the ground, even in very large specimens like salt water

> crocodiles.  In fact, what IS the height of the tallest living reptile?  And

> crocodiles have a 4 chambered heart.  High blood pressure is a relative

> term, after all.  To me, this argues for sauropods being at least partially

> endothermic.  And, Brachiosaurus has a shoulder height of 23-25 feet &

> that's taller than the tallest recorded giraffe

>       (19 feet).  So, the height is already so great that the animal isn't

> viable unless it's cardiovascular system were designed to pump blood to a

> great height.  Unless the neck is designed to be held horizontally, then

> THAT posture (especially with a 20 foot long neck) would put tremendous

> strain

>       on the structure.  With the right sketal structure & ligaments,

> tendons, & muscles; more erect could 

>       require less effort to maintain.  Gravity is gravity: it pulls with

> equal force on everything  of equal mass & an animal must by definition be

> strong enough to move it's own bulk.  That's what gets older humans in

> trouble who lose muscle mass (IF they do) as they age.  But, I still think

> their is a clue in the obvious height above ground level limit on modern

> terrestrial "ectotherms".  A 16 foot long, 

>       1500 pound "salty" is what; perhaps 2 feet tall?  This "constraint"

> is obviously far less rigorous on

>       we terrestrial endotherms.  

<teensy snip> 

============================================================
==============================================================

Well, that's kind of a grey area. Many of the large reptiles died out already,
plus many mammals are medium to small creatures.

If we look at a 17 ft Nile crocodile, it ends up standing at around the same
height as an 9ft lion. Both are predators and in such cases, be they reptiles
or mammals, the height stays about the same for both. It just seems to be a
constraint of modern times. Most living predators don't stand much taller than
3 or 4 feet (these must be very modern times, since Megalania and Purussaurus
would have had something to say on that)

Now in the herbivore category we get the bigger animals. Since everyone
already knows about the largest mammals, I'll just go to the reptiles, the
largest reptile herbivores (and tallest reptiles) are Aldabra and Galapagos
tortoises. Animals that are often seen in a posture that is very sauropod like
in design, with the neck held in a nice S curve to the body.

These turtles don't seem to find that much trouble with keeping their long
necks held so much higher than their bodies and they only have a 3 chambered
heart.

Now when moving, their heads become more level to their bodies, but when at
rest or surveying the terrain, they keep their necks held high. I could see
the same for sauropods. Keeping the neck rather low while walking and then
high while resting and feeding.

Then of course their is the ever so strange Tanystropheus and Keichousaurs.
Have to wonder how they positioned those necks and how they kept the blood
flow going.

All these questions.

Archosaur J

Jurassosaurus's Reptipage: A page devoted to the study of the reptilia

http://members.tripod.com/~jurassosauridae/index.html

____________________________________________________________________
Get free e-mail and a permanent address at http://www.netaddress.com/?N=1