|MadSci Network: Engineering|
This is a difficult question, partly because it is very open, secondly because it is a little off from my field of expertise. There is no absolute advantage to either kind of skeleton. As you have found, the lobster can at least crush a human finger joint, possibly even cut off a small human finger, but at the same time, a human can rip a lobster's claw right out. So the advantage of the situation seems to depend more on who grabbed first than on the specific type of skeleton. Now, all other things being equal, If a lobster were to attack a vertebrate its own size, I'd put my money on the lobster. The mechanical advantage in this scenario stems from the fact that the lobster simply has lots more bone. to protect it (in proportion to its own size), and the bone in the claws is shaped in a curved way that enhances its strength. A small vertebrate would likely have very little bone, surrounded by much softer tissue. So, in short, the advantage is all because of the large amount of bone, and the fact that it is on the outside. Exoskeletons are generally better for smaller animals because it provides the best protection. On the other hand, an exoskeleton requires molting for growth (the old skeleton is shed away periodically. Until the new crust hardens, the crustacean is very vulnerable to attack. For larger animals, an exoskeleton would have to be excessively heavy to be of an advantage. The molting cycles would have to speed up as the animal grows to maintain a particular rate of growth, but at the same time, the amount of material required to create the new skeleton increases, which seems to require slower molting cycles. So, there has to be a maximum size at which growth can no longer be sustained effectively. (Comment by reviewer: while weight certainly is an important factor, it does not limit the seizes to what we see today. A much more limiting factor are the problens in getting oxygen and nutrients dristributed throughout the body, as well as getting rid of breakdown products and carbon dioxide. All animals with exoskeleton do have a comparatively simple heart, open blood circulation and a system of trachea for gas transport. I once learned that these are the limiting factors for the growth of animals with exoskeletons.) If we observe in nature, all those facts seem to be reflected in the evidence: animals with exoskeletons tend to be smaller than animals with endoskeletons. At the same time, there are many more animals with exoskeletons on the planet than animals with endoskeletons. So there is clearly an advantage, as long as they are small animals. An endoskeleton is not as protective, but it allows larger species to grow, and thus be able to escape total domination by spiders crabs and lobsters. I have gathered some good resources you may find useful, about lobsters and their claws. http://www.vattenkikaren.gu.se/fakta/arter/crustace/decapoda/homag amm/homa gake.html http://www.mainelob sterco.com/faqsclaw.htm#faqs http://www.lobsters.org/ ldoc/ldoc1101.html http://www.museum.v ic.gov.au/crust/lobbiol.html http://www .calgarypubliclibrary.com/cya/sra2001/crus.htm Your mad scientist, -Aurelio R. Ramos
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