The following messages come from an exchange on talk.origins between myself (Phil "Pib" Burns) and Ted Holden, who for a number of years was the principal proponent of Velikovskian and Saturnist style catastrophism on the talk.origins USENET newsgroup. Mr. Holden believes that large dinosaurs such as sauropods could not have existed if the Earth's gravity matched its current strength. He suggests the Earth's gravity was reduced by its close proximity to the proto-Saturn during the age of dinosaurs, or that some kind of electro-magnetic effects reduced the felt effect of gravity at the Earth's surface. You can find out more about Mr. Holden's ideas on his web page about Reality and Dinosaurs.
In the first message I comment on the possibility that some sauropods may have had nuchal ligaments to assist them in supporting and moving their long necks.
In message 24 Sep 1994 10:11:27 -0400, Ted Holden writes: > > Basically, what I said was as follows: that if it would take the > muscular strength of a neck 30' in diameter to handle the 430,000 > foot-lbs of torque in an ultrasaur's neck, and if the ultrasaur's neck > was only six or seven feet in diameter, and if the entire thing were > being held up by a ligament, since muscular strength was obviously not > even ballpark for what was needed, then the creature would never be able > to lower its head (against the steel ligament) to drink. > > Throop or somebody replied "Ah! But the ligament was
, i.e. > inelastic enough to support a neck many times heavier than available > musculature could handle, but very elastic whenever needed for drinking > or whatever. Just another unfalsifiable doctrine from the t.o howler > monkey crew. > Elastic nuchal ligaments exist in a number of extent animals. The ligaments relieve the animals of the need to use muscular power just to hold their heads erect. Moving the head requires muscular exertion. It is true that the neck and spinal column bones of the majority of sauropods exhibit fissures which might have contained a single long nuchal ligament, or a series of short ligaments like those of birds today. R. McNeil Alexander, in his book "Dynamics of Dinosaurs and Other Extinct Giants," discusses the mechanics of a nuchal ligament using the Diplodocus as an example. (Incidentally, he derives a figure for the force acting on the neck which is considerably lower than yours. You might want to compare your calculations with Alexander's to see the difference.) Alexander suggests that a ligament as thick as the spinal furrow allows would just barely support the neck of the diplodocus without breaking. This neglects any load borne by the neck muscles. Since neck muscles do bear part of the load in birds and other existing animals with nuchal ligaments, it is reasonable to assume that the same holds true for sauropods, and therefore that the combination of nuchal ligament and muscles would be sufficient to hold up the neck (and tail, for that matter). However, the spinal column bones of Brachiosaurids, which appear to have held their necks erect like the giraffe, do not exhibit a deep fissure for a nuchal ligament. Perhaps these animals used a series of short ligaments like birds, or perhaps they used some other mechanism altogether.
In the second message I comment on the blood pressure problems for sauropods raised by Mr. Holden. The need for a very high blood pressure is a valid point but I doubt this requires reduced gravity to explain it. It is more likely that large sauropods possessed an adaptation in their soft tissues whose existence we can only guess at.
In message 30 Sep 1994 11:49:08 -0400, Ted Holden writes: > Once again, the comments I am seeing all seem to have missed a point > involving the diplodocid/brachiosaur dichotomy. Throop and others are > still claiming that the brachiosaurs held their necks upright, because > they appear not to have the attachments for a ligament which would be of > any help in holding their necks outright (in our gravity of course). > McGowan and the other scientists who have made the case for low-held > necks due to blood pressure problems, however, are making no special > allowances for the brachiosaurids; they would have to hold their necks > outwards too, regardless of what structure might tell you would come > naturally to them. The brachiosaurids would be truly sol in our world, > not being able to hold their heads upwards, nor having any prayer of > holding them outwards either. > As far as I know, paleontologists still maintain the Brachiosaurs held their necks erect. Given the skeletal remains, this appears to be the best way to reconstruct the animal. In this sense, the Brachiosaurs resembled giraffes. Hence, the problems giraffes face are magnified for the Brachiosaurs. Giraffes reduce the dead air space in their windpipes through tracheal stenosis. Could the sauropods -- particularly the Brachiosaurs -- have done the same? How much dead air space is it feasible for an animal to tolerate? Does the placement of the nostrils at the top of the head of Brachiosaurs and other sauropods provide a clue? There are pneumatic ducts and cavities, including large pleurocoels, in the back and neck of all the sauropods. The Brachiosaurs also exhibited extensive pneumatic openings in the ribs. Can we assume these were air-filled as similar openings are in modern animals which exhibit them? In birds, for example, these openings are filled with air via complicated connections with the lung/air-sack system. It does not seem unreasonable to speculate that the same thing was true of Brachiosaurs. The whole skeleton of these animals appears to be designed to save weight. If gravity were greatly reduced we would not expect to see such excavations in the bones. For example, whales do not show any of these types of excavations since they rely on the water to support them. The giraffe has the highest blood pressure of any living animal. The blood pressure for sauropods would have needed to be much higher than that of the giraffe. R. S. Seymour pointed out in a paper in Nature in 1976 that, in the absense of a dense supporting medium (e.g., water), sauropod hearts would conservatively need to be very thick (e.g., undergo myocardial hypertrophy by a factor of at least eight) in order for the walls of the ventricles to handle large stresses in excess of 500 mm Hg. He suggested Sauropod hearts should weigh between 1.2 and 3.2 metric tons. But the thicker the wall, the more difficult becomes the oxygenation of the myocardium. How could a Brachiosaur feed with its neck extended at full height? We need not assume that the Brachiosaurs (or other sauropods, for that matter) required enormous systolic blood pressures. Instead, sauropods -- particularly Brachiosaurs -- may have been able to tolerate extended periods of hypoxia. Perhaps sauropods possessed a carotid sinus serving as a reservoir to oxygenate the brain. Perhaps sauropods possessed an auxilliary carotid pumping system. Perhaps the unusual position of the nostrils suggests some other type of direct oxygenation adaptation. In giraffes, the rete mirabile at the base of the brain is very elastic. This prevents hypertensive failure of the cerebral vascular system when the head's elevation changes rapidly. It is very likely that Brachiosaurs, at least, had a similar adaptation. Could a large sauropod survive a fall? I don't think anyone has yet proposed a definitive answer to that question. How much food did a sauropod eat each day? This would depend upon whether sauropods were tachymetabolic endotherms, or -- and I think this is more likely -- they were inertial or even fermentative homeotherms. What exactly was the diet of sauropods? How much did they eat each day? A typical estimate for a smaller 15 ton sauropod would be about 200 kg of forage per day. This seems quite feasible. One might expect larger sauropods to eat more, and this would still be reasonable. However, it does not seem likely that the very large sauropods like Brachiosaurs could have gathered enough food in a day if they were tachymetabolic endotherms. We know very little about how sauropods reproduced. We don't know if they laid eggs or gave live birth. There are one or two sites where eggs have been found that might be those of sauropods, but the identification is very tentative. We don't know how fast sauropods grew, although they seem to have grown at speeds more like those of endotherms than ectotherms. We don't know how long they lived, although we might guess somewhere around 100 years since life expectancy usually correlates positively with body size. There is indeed a lot we don't yet know about sauropods. They were unique animals quite unlike anything before or since. I don't believe, though, that we need yet to postulate a significant reduction in gravity to explain how these animals functioned, but then I'm a conservative fellow :-}. As more fossils of the particularly large sauropods are found, we may be able to close in on some of the answers to the questions that still puzzle us about these extraordinary creatures.
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Last modified by pib on July 6, 2003.