Re: On rearing in sauropods

[Heinrich Mallison <heinrich.mallison@mfn-berlin.de>]

>> When asked about the blood pressure problem, the author
>> said that some kind of simple adaptation must have been
>> present anyway just to let the animal lower the head to
>> the ground and back to a horizontal neck posture.

To clarify: my answer at the conference what not very good, as I forgot 
to mention the obvious:

The whole problem of blood pressure, as detailed succinctly by Seymour 
(see http://www.sciencemag.org/cgi/content/full/323/5922/1671), only 
exists if blood flow to the brain is not separated from that going to 
the rest of the body. Much as the pulmonary system has a different blood 
pressure than the rest of the body in all(!) animals with parasagittal 
limbs, a similar pressure separation could allow extremely high 
pressures in the neck, on a limited blood volume. After all, how much 
blood do you NEED for a 1/4 pound brain?

I had a very nice chat with Roger Seymour in the course of the sauropod 
meeting in Bonn, and we agreed that
- a system as detailed below is feasible,
- could solve all problems,
- and sadly would be completely restricted to soft tissues. Thus 
untraceable in fossils. Sorry!

Here's what I imagine as a required preadaptation: Basal dinosaurs, and 
some of their archosaur ancestors, had fairly long necks. Cause, mainly, 
by the parasagittal limb posture in combination with a short skull, 
because the only way to stay flight-ready when drinking/feeding close to 
the ground is have a long neck. This neck has additional benefits, such 
as the ability to simply yank it out of the way of a predator's bite 
rather quickly. This, however, means a rough doubling of the height: 
bottom -> shoulder level plus shoulder level -> maximum height. Even for 
an animal with a 1.5m shoulder height, this evasive maneuver already 
results in a 3 m lift, and any adaptations such as rudimentary 
non-return valves formed by a simple wall duplication in the carotids 
would be beneficial.
Once these vales exist, the blood pressure in the carotids can be 
increased massively by simply creating a widening at their base, whcih 
gets filled with blood at normal systemic pressure (systolic phase), and 
using contractions of the muscular walls in phase with the diastole to 
pump blood up into the narrow parts, to the brain. A sauropod neck 
leaves ample room for such 'second heart' cavities, and arterial walls 
are muscular anyways.

Evidence? None, sadly!

So the question remains why we do not see anything similar in extant 
animals - but do we? AFAIK nobody has ever been able to measure blood 
pressure in giraffe necks during rapid up and down motions 
simultaneously with carotid diameter and blood flow velocity. I would 
not be surprised if they helped their blood along up the neck with 
peristaltic contractions of the carotid walls while they lift their 
necks up.

I guess we will never know how sauropods did it, but motion analysis 
based on articulation and manual manipulation of specimens indicates 
that most sauropods could lift their necks up high (Christian & Dzemski 
2007). Stevens & Parrish (e.g. 1999) disagree, but I both distrust some 
of their assumptions (sorry, Kent!), and my imagination breaks down when 
I try to imagine a diplodocid attacked by theropods. The neck is a 
wonderful target, and I imagine the poor beast able to lift the head up 
high to avoid the attack, but fainting ASAP due to blood pressure 
problems and falling to the ground before the astonished hunters as 
'meals on wheels'.


>> Outside of his talk, he also talked a lot about the rest
>> of his recently finished PhD thesis. We can look forward
>> to a lot of very interesting and very, very, very, very
>> well argued papers.

Well thanks, David, for getting people's hopes high - it is now my turn 
to disappoint them ;)


lit cited:
Chrisitan, A. & Dzemski, G.** (2007): Reconstruction of the cervical 
skeleton
posture of *Brachiosaurus brancai* Janensch, 1914 by an analysis of the 
intervertebral
stress along the neck and a comparison with the results of different 
approaches - 
Fossil Record 10(1): 37-48.

Stevens, K.A. & Parrish, J.M. (1999): Neck posture and feeding habits of 
two Jurassic
sauropod dinosaurs. Science 284:798â800


btw, the meeting abstracts are available here:
http://www.naturalsciences.be/science/colloquia/vertebrateevolution

direct link to PDF:
http://www.naturalsciences.be/common/pdf/science/colloquia/Darwin_Bernissart_abstracts_guidebook.pdf


--

Dr. Heinrich Mallison
Museum fÃr Naturkunde - Leibniz-Institut fÃr Evolutions- und
BiodiversitÃtsforschung an der Humboldt-UniversitÃt zu Berlin
Invalidenstrasse 43
10115 Berlin


Tel: +49(0)30-2093-8764
Email: heinrich.mallison@mfn-berlin.de