Sauropod necks -- again!

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

Hi all:

This is a response to the recent questions on sauropod necks.  Lifting a 
neck is usually accomplished both actively (through neck muscles 
contracting) and passively (through the rebounding action of a ligament).  
Big-headed mammals have what's called a nuchal ligament, a large band of 
elastic tissue that stretches when the head is lowered for feeding.  When 
the animal wishes to raise its head back up, the stored energy in the nuchal 
ligament helps the mammal raise its big head back up.

Sauropods have relatively small heads for their body size, but the tall 
neural spines in the region of the shoulders of many sauropods may have 
acted as an anchoring spot of a type of nuchal ligament that allowed the 
same sort of thing to take place.

How does something with a 40 ft neck reach its food?  Depends on who you 
talk to.  Since I work with Parrish and Stevens and have seen the computer 
work they have done on diplodocids and are doing with a camarasaur, I would 
suspect the neck of this big guy was held well above the ground (perhaps 20 
feet or more at the shoulder) but was perhaps like a rather straight beam.  
In this case, the animal would act like a large, stationary vacuum, feeding 
up, down, and side to side in a wide feeding envelope but not up to 40 feet 
in the air.

The trouble is, we do not have a good transition from the dorsal verts to 
the cervical verts in brachiosaurs or camarasaurs and so we do not know for 
sure if these animals had horizontal or diagonally held necks.  While many 
sauropod dinosaurs are found in a death pose with their heads and necks 
kinked far up over their backs, this only tells us what these animals did 
with their necks when dead.  With luck, a clear transitional series will 
avail itself and someone will finally sort out whether camarasaurids and 
brachiosaurids held their heads high or more straight out.

One little note on the Maryland Astrodon/Pleurocoelus.  Having looked at the 
ulna of that little guy, the olecranon process is like it is in other 
sauropods -- very reduced.  In titanosaurids, the olecranon is secondarily 
developed and unmistakable.  This being the case, I have my doubts about a 
titanosaurid affinity for that animal, but stranger things have happened.

Whew, back to dead reptiles,

Hope this helps,

Matt Bonnan

Allosaurus, Tyrannosaurus, and "Nanotyrannus"
None of these guys had a U-shaped sauropod manus

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com