friesen@psivax.UUCP (Stanley Friesen) (09/03/85)
I went to the UCLA library Saturday and traced down a few of the references I have mentioned in the last few weeks. Unfortunately, one of the journals was at the bindery, so I couldn't find all the articles I was looking for. I have therefor decided to post the references as a series of articles, with a mini-review of the more important ones. Alexander, R.M, 1985. Mechanics of posture and gait of some large dinosaurs. Zoological Journal of the Linnean Society 83:1-25 This article covers alot of ground. It gives estimates of the mechanical factors influencing dinosaurs and how htese would effect the dinosaurs in life. Several of the factors bear on the issue of whether or not suvh animals could have supported themselves on land and moved at reasonable speeds. Dr Alexander himself does not actually address these issues, he treats them as if they have already been solved. There are several references mentioned in his bibliography which *do* address these issues. In fact the bibliography is a very good one, and is worth some attention. The first calculation on the support capacity of the dinosaur skeleton is the calculation of the stress components on the vertebral column. It is interesting to note that the estimated intervertebral compression for the Sauropods("Brontosaurs") is *one* *third* of that generated in the *human* backbone by our vertical posture! Thus the backbone could *easily* support the weight required of it. In another section, where he is trying to get some idea of dinosaurian gait(rate and phase of limb movement - not actual speed), he calculates what I will call a limb load factor. This number is in effect the amount of weight a limb *could* support divided by the amount of the actual weight of the animal it *is* supporting. Thus a load factor of one would indicate that the limb in question could support the required portion of the animals weight, but *nothing* else. A lower factor would indicate insufficient strength to support the weight, and a higher value would indicate excess capacity. Dr Alexander uses this to estimate the maximum pace for some dinosaurs. This works because during locomotion excess stress is placed on the limbs when they hit the ground on the down stroke &c. This excess is greater the faster the legs are moving, thus a galloping animal requires a much larger load factor than a standing animal, and even walking will require a factor somewhat larger than 1.0. An Elephant has a load factor of *aproximately* 10 and can go at a "slow", shuffling gallop(just a touch faster than a walk). The *lowest* reported estimate for any dinosaur is *three*, which is plenty large enough for walking on land, and Dr Alexander estimates the load factor for the *same* form(Diplodocus if I remember correctly) at *five*. It is interesting to note that the load factor for the heavier Sauropod, Apatosaurus(ex Brontosaurus), is essentially the same as that of an Elephant! Thus there is no reasion to assume that the low load factor for Diplodocus is due to weight, it appears to be due to its lightness of build(that is assuming my memory is right). The basic result is that even the larger Sauropods have sufficient limb support to walk about on dry land, and in many cases to even gallop a little. The load factor for Tyrannosaurus is also about the same as an Elephant, thus the statement by someone on the net that it couldn't exceed some ridiculously low speed without breaking its legs is also baseless. And Triceratops had a sufficiently large load factor for full scale galloping, despite being as heavy as an Elephant. Of course, as Dr Alexender points out these pace estimates assume that dinosaurs used the same safety factor as a modern Elephant, which is certainlyy reasonable in the case of Sauropods, but may well need to be revised for things like Tyrannosaurus. Well, this seems to have come out longer than I intended! I think I had better stop now. -- Sarima (Stanley Friesen) UUCP: {ttidca|ihnp4|sdcrdcf|quad1|nrcvax|bellcore|logico}!psivax!friesen ARPA: ttidca!psivax!friesen@rand-unix.arpa