ImagingGeek,
Not defending Mansfield's Hypothesis but questioning your assumption that (surface) gravity could not have been less during the reign of the dinosaurs.
It's not an assumption; I provided two papers - one analyzing paleomagnetic data, the other tidal sediments - to measure the mass of the earth over its history. They clearly showed there has been no change in the earths mass.
You gave a link-reference relating to pterosaurs and their ability to fly. What is your opinion concerning the Japanese scientist Katsufumi Sato, whose extensive study of modern sea birds leads him to conclude that pterodactyls were too heavy to fly. I assume his conclusion is based on the premise that gravity has been the same in the past.
I'd say a few things:
1)pterosaurs are not birds, nor are they related to birds (i.e. they're not even dinos, which are the evolutionary predecessors to birds). Ergo, any comparison with birds will be fraught with issues.
2) Aerodynamic analysis, as described in the papers I linked to, showed that pterosaur wings were able to produce sufficient lift for them to fly/glide.
3) We know that the atmosphere had a higher O2 concentration in the pterosaurs day, and may have been denser as well. Ergo, even bird-scale dynamics may have worked under those conditions.
4) They must of flown or glided - pterosaur physiology is not well adapted to life on the ground - evolution would pretty quickly eliminate them if they couldn't fly.
Your other link about large dinosaurs seems to require a subscription to view the report. Any other references?
Unfortunately, many scientific papers are behind subscription walls. I'm sure there are free sources out there that describe dino biomechanics, but I am unaware of where those sources may be. If you really want the paper, drop me a PM with your e-mail and I can send you the PDF.
Bryan
EDIT: To summarize what the above paper discusses, its an analysis of the forces generated as various large dinosaurs walked. It then compares those forces to known biological materials (i.e. collagen and lammanin; proteins which "glue" our bodies togeather). A few quotes:
The cervical and anterior dorsal vertebrae of Diplodocus have bifid neural spines (Fig. 4C). The notch between the two branches of each spine was presumably occupied by a tension member (either a ligament or a muscle) that supported the head and neck by counteracting the hogging moments due to their weight. The third dorsal vertebra will be considered because it has one of the biggest notches and because Hatcher (1901) supplied a scale drawing of its posterior face. The supposed tension member presumably at least filled the notch, but it seems quite likely that it may have projected above the neural spine as indicated by stipple in Fig. 4C. Calculations will be made for a member of the dimensions so indicated, but it should be remembered that it may have been larger or smaller. The stresses that will be calculated are subject to error for this reason, and also because of possible errors in the estimation of the hogging moment.
The centroid of the stippled cross-section is 0.66 m above the centroid of the face of the centrum. The hogging moment to be counteracted is about 50 kN m(from Fig. 4B). Hence the force to be transmitted by the tension member is 50/0.66 = 76 kN. T h e stippled area is 0.09 m 2 so the stress in a tension member of the dimensions shown would be 76/0.09 = 800 kPa. The compressive force on the centrum would also be 76 kN. It would set up a stress of 1.2 MPa in the intervertebral disc.
What kind of tension member could have exerted the estimated stress of 800 kPa? This stress is two orders of magnitude less than the tensile strength of collagen (Wainwright et al. 1976) so a collagen ligament would have had a ludicrously high factor of safety. It is the same order of magnitude as the tensile strength of elastin, which seems to be of the order of 2 MPa (inferred from data in Gosline, 1980). Thus an elastin ligament (like the ligamentum nuchae of many mammals) seems possible.
That particular quote deals with
Diplodocus's spine, and the forces it would experience based on the weight of the animal suspended between its front and hind legs. They do similar calcs for the legs and other parts of the animal, and show that in all cases the tensile and compressive strength of the proteins and bones animal bodies are made of are more than ample to deal with the mass of the dino.
