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It's not just Mackovicky et al who have shown what can be done when you fail to follow basic principles all science PhDs are supposed to learn: Read around the subject; Do proper science - ie see which of ALL the theories best explains the observations. The BBC TV programme (fronted by Bill Oddie) showing how well a mechanical model of a dromaeosaur's leg and claw cut flesh, for some reason best known to itself, reconstructed the slashing toe claw with a blunt edge. Where shall I start?! OK - the evolution of ripping weapons. It was claimed by one palaeontologist in or around the programme that dromaeosaurs had "razor sharp teeth". Even though they weren't razor sharp, if he admits the teeth had clearly evolved *some* specialised form, why did he not consider the possibility that the toe claw also could have evolved an extreme edge for cutting? After all, it had evolved a number of other extreme adaptations! The toe claw was clearly held clear of the ground, and that should have brought to mind the different conditions of dog and cat claws, which is of some relevance to the issue. The massive flexing tendon underneath shows the claw could withstand enormous flexing forces, and much if not most of this force will have been borne not by the horn sheath but by the bone core. The tension would apply to the underneath of the core; the cross-section in the lower-half of the core would have needed to minimise the stress concentrations so would not have been sharp underneath. Is there some reason why the horn sheath needed to be of exactly the same shape as the bone core? A buzzard's talons have a cross-section of an inverted splay-armed "U", basically flattish across the bottom, but with the two edges very sharp. (This sharpness is for slicing into flesh, but only a bit, just enough to allow the claw to penetrate adequately with ease even if it hits a sheet of ligament or something. Predators' prongs tread a fine line between holding flesh fast without shredding it and allowing the prey to escape - as with fish eaters (including even big crocs, which aren't optimised for zebras) which don't have sharp edges or beading around the edge since this tends to slash, and pure dismemberment as in theropods. Dogs etc. have teeth for grabbing and not slashing, and other teeth for cutting. Next time you see a man in a kilt, see if he's wearing an osprey's foot somewhere - surprisingly often he will be, perhaps on his sock. The edges of the "U" have teeth, designed not for slashing but for friction.) If a buzzard can have very sharp edges to its talons, why can't dromaeosaurs? Absolutely no reason. Absolutely every reason to give the mechanical claw a good edge just for the sake of the experiment. And if you can have teeth with serrations, why can't you have them on claws? If they really wanted to do a good experiment they might as well have compared the cutting efficiency with and without a sharp, possibly serrated edge. Indeed any idiot could buy a lump of hardwood and whittle it down to the shape of a dromaeosaur claw complete with serrations and also a handle, buy side of pork or something, and see if a fit human arm in emergency mode could could cut a three-inch slash in three seconds. Bear in mind the dromaeosaur would be that much more practised, 100% committed, and have hotter and therefore more powerful muscles. But it's not just the claw that says it was used for killing. As I've said time and time again dromaeosaurs' teeth were not resistant enough to sideways forces to be used on struggling prey. The teeth were not only very thin but were also swept back at such an angle that serious twisting forces would have been applied to the roots if prey struggled sideways. This torsion would not only increase the tendency to snap at the root but would also tend to twist the tooth in its socket. Not only do the teeth go with the claw, it is also not a coincidence that the claw goes with the tail. The characteristic tail of dromaeosaurs would have been an appalling inconvenience for absolutely every activity except the one it was designed for, especially for flying droms. It is NOT like a cat or squirrel's tail. Anyone trying to theorise about anything involving dromaeosaurs might as well not bother unless their theory convincingly explains that tail which would would halved in length and stiffness in a thousand years unless it served a purpose no other animal enjoyed, instead of lasting 80 millon years. The explanation is in: http://jerwood.nhm.ac.uk/archives/paleonet/2003/msg00009.html , and it does involve a slashing use for the claw. The claw was curved because it allowed the edge to be pressed against the substrate and sliced across it by extending the leg and rotating about the base of the claw. Less efficient alternatives would include: having a straight claw and slicing by rotating the whole leg, diluting the force by rotating about the hip; having a straight claw with the claw at an angle to the leg and applying force to the edge by straightening the leg, but finding the claw pops out every time you pull back to apply another saw-stroke. With the geometry they used, you could saw as you pushed the claw in, with tension on the flexing tendon, and also on the way out, still with tension on the flexing tendon, but allowing the hooked end of the claw to stop it popping out completely. (The actual angle of the claw would be more extended on the pushing stroke, and flexed on the pulling.) Anyway, with the edge in the shape of a spiral like that, cutting by actually rotating about the claw's joint allows the angle of attack to be shallow early on when the point is only just in and the moment of resistance is high, but steeper when the point of contact with uncut fibres approaches the joint and reduces the moment. As with most things, it was best done with the eyes and mind open, which is why Manning, PL., Payne, D., Pennicott, J., Barrett, PM., Ennos, RA. were wasting their time and my money in making the programme. __________________________________ Yahoo! FareChase: Search multiple travel sites in one click. http://farechase.yahoo.com
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