lateral lines on sharks do what?
823692
Have a look here:\nhttp://www.bbc.co.uk/nature/animals/features/287feature2.shtml\n\nAnd here:\nhttp://users.aber.ac.uk/sac5/characteristics.htm
609755
It's a good question, and one that is still not fully answered.  When we speak of "instinct," as some of the other answerers did, we actually asign the problem to a black box and leave it pretty unanswered.  Instinct alright, but the question remains: HOW?  \n\nNow, there are two means that have been found to be apparently of importance for migrating birds.  One is magnetic field orientation, the other is visual orientation.  Both seem to be involved partially or exclusively, but how exactly they work remains a bit of a mystery.\n\nIn order for an animal to orient itself along the magnetic field of the earth, it has to somehow sense the field.  This can either work by means of having magnetic substances in the body, that will align according to the magnetic field.  Their alignment must then be sensed by the organism.  Some organisms have magnitide enclosed in their body that serves this function.  However, in birds nothing like it has been found.  Nevertheless, birds do use magnetic fields, and so the question remains: HOW?\n\nElasmobranchs (sharks, skates, and rays) actually orient themselves according to the earth's magnetic field using electric currents.  It's a simple but very impressive physiological achievement.  If you move a charge through a standing magnetic field, you will induce an electric current.  This is due to the Lorentz force, which will act on the charge (F = q v B sinØ).  The right hand rule will give you the direction of the Lorentz force.  If the shark swims in an eastern direction, the Lorentz force will pull upwards, so that the direction of the induced electric field is a dorso-ventral one (i.e., one pol is on the back of the animal, from where the current flows to the other pol on the belly of the shark).  If the shark were to swim the opposite direction, the electric current would run the other way.  With its electrosensitive organs (Ampullae of Lorenzi), the sahrk can sense the direction of the current and figure out which direction it swims.  It's an electromagnetic compass.  However, birds have no electrosensitive receptors...\n\nNow, birds also use visual cues.  These seem to be primarily stars, which is of course great for navigation.  Landmarks, like mountains etc. may also play a role.  \n\nBut again, how this works in detail is not fully understood.  Let me know once you figure it out!!!
520975
That's an interesting question!\nThe short answer would be "Different evolutionary paths", which is true. But those paths imply adaptive and functional differences. \nThe teeth of sharks are not too different from those of other tetrapods. Aside from birds, most tetrapods have many generations of teeth (this is called polyphyodonty), and those teeth are usually not strongly attached to the jaws. They`re more or less easily lost and replaced during normal activities. So, why don't we mammals have such a useful feature? \nThe loss of all those teeth replacements was a tradeoff for our acquisition of better tooth occlusion. Occlusion is the way the surfaces of the upper and lower teeth contact each other, and in mammals, our chewing teeth (molars and premolars) have complex occlusal surfaces, which allow for slicing food (shearing like scissors), crushing food (cusps and basins that act like a mortar and pestle), and other ways of basically, disintegrating food items. \nThe thing is, the precise interlocking of cusps and vales is not easy to achieve (as anybody with occlusion problems has probably heard from the dentist). So the hypothesis is that the evolutionary path of mammals "focused" on one generation of perfectly occluding teeth. Thus, molars erupt late in life, grow slowly, and are not replaced. And the other teeth (incisors, canines and premolars) have a first, "milk" teeth generation that allows the young mammal to feed while its skull is expanding. Then, by the time its growth has slowed down, the definitive teeth erupt and take their places (they would not fit in the small jaws).\nThe teeth of man, as those of all primates, are brachydont. This means that they don't keep growing once they've erupted completely. However, the enamel that forms the outer cover of the teeth is the hardest substance in our bodies, and is able to endure the wear from our food. However, many other mammals that eat more abrasive foods (plants, and especially grasses) have permanently growing teeth (hypsodonty). This is, in a way, the equivalent of having multiple generations of teeth; their teeth keep growing throughout part of their lives (as in the case of horses) or all of their lives (like many rodents and ruminants). But we cannot "recover" the capacity for multiple teeth generations that we "gave up" evolutionarily when we became mammals.
562934
It is a myth that sharks have to constantly swim or else drown.  As so often with exotic animals, apex predators in particular, we find such stories to be passed on through generations, and even tons of excellent studies on the animals cannot change commonly held opinion.  What is the basis for this wrongly held believe?\n\nMost "fishes" breath by producing a conintuous water flow over their gills making use of what is called the buccal/opercular pump.  You surely have observed fish in an aquarium before, and have noticed how they rhythmically open and close their mouths.  What you may or may not have seen was that in the same rhythm, only slightly delayed, a bone on the side of the head opened and closed.  What you saw was the buccal/opercular pump at action.  The bone on the side of the head was the operculum.  It covers the gill openings with the gills.  When the fish opens its mouth (i.e., the buccal cavity), the operculum is closed.  The fish fills its mouth with water rich in oxygen, opens the operculum and at the same time closes its mouth.  As an effect, the water is being pressed out through the gill openings and over the gills.  Next, the operculum is closed while at the same time the mouth opens and the cycle is repeated.  By this form of active breathing the animal can indeed achieve a constant flow of water over its gills. \n\nSharks, like all other elasmobranchs (i.e., sharks, skates, and rays) do not have operculi.  Instead, their gill slits are visible at the side of their heads.  Early biologists thought that sharks therefor could not be stationary at the sea bottom, since without an operculum they could not achieve water to flow over their gills and would certainly - believe it or not - drown.  Not quite so.\n\nIt is true, sharks usually breath "inactively", that is they achieve a constant water flow over the gills by swimming with their mouth slightly open.  But quite frequently, sharks can be found stationary on the bottom, where they breath actively.  Like teleost they achieve this feat by opening and closing their mouths.  The lack of operculu certainly makes this form of breathing less sufficient, but the gill openings are constructed like window blinds that are partially closed (or opened, in case you are an optimist...).  In other words, water can be pushed through in one direction, opening the gill slits, but if it were sucked the other way the individual skin flaps collapse on top of one another and close the openings.  It is not the most efficient form of breathing, but it works.  \n\nAt times, you will find animals that hover on the sea floor positioned in a moderate water current so that by simply opening their mouths the current constantly moves water over their gills.  But even without this current, sharks can do quite well breathing actively on the floor.\n\nI suggest, you take your son to an aquarium and check out some of the sharks on display.  I am sure their will be one or two specimens hanging out happily on the floor demonstrating what I just described.\n\nHope this helps.
74215
I agree with big brain, they are some of the most efficent and dangerous killers in the animal kingdom. \n\nAlthough they do have communication patterns. Male crocodiles let out a low grunt when they are searching for a mate. And baby crocodiles let out a high pitch grunt when they are in danger. Not too sure about the sharks though.\n\nMost of the time though as big brain said they are solitary animals.
177529
oarfish are very weird and interesting fish.  one species is fantastically long and skinny, up to 50 feet long (and may be the source of many stories about sea serpents).\n\nvery little is know about them, and it wasn't until a few years ago that anyone actually managed to film one alive.\n\nthey feed primarily on zooplankton, straining little copepods and other little yummies from the water.  they might also take small fish, and jellyfish when they can.\n\nlarval and juvenile oarfish are sometimes found floating near the surface, basically part of the zooplankton themselves.  they probably don't have much interaction with the adults.  the adults are solitary, and don't have much interaction with each other either.\n\nthey are probably food for any number of pelagic predators like big sharks, but that's about it for interactivity.
184692
Fishes have eyeballs, two of them in their optic capsules, just like all other vertebrates. They're surrounded partly by bone, and partly by an elastic but resistant capsule. \nBony fishes don't have eyelids, but sharks and rays do\n(see answer at \nhttp://answers.yahoo.com/question/index;_ylt=AqPoH8mhQReCU_CYDM1Fvirsy6IX?qid=1006030500996 )\n\nAnd they _do_ have nostrils, but, as you have rightly deducted, they're not used for breathing. \nIf you look at a bony fish (a goldfish or whatever you have at hand) you'll see that it has TWO nostrils on each side of its snout (they can be close together or really distant). Between these two nostrils of each side there is a tube with special olfactory (smelling) cells, like the ones we have in our own noses. The water with chemical "smell/flavor" molecules goes in through the anterior opening, and flows out through the posterior opening. Thus, fish nostrils (derived from the primitive pair of olfactory capsules) are used for smell/flavor perception, and not for breathing (which occurs at the gills). \nIt's only in tetrapods (from amphibians to reptiles, birds and mammals) that the connection between the nostrils and the respiratory system occurs (and the lungs appear). If you open a frog's mouth (please only try it with a dead animal!) you'll see two paired holes in the roof of its mouth. Those are the internal nostrils (called "choanae") and they allow passage of breathing air to the mouth--> pharynx--> lungs. \n\nAdditional trivia:\n- Our own internal nostrils open way back in our pharynx, because we have a secondary palate.\n- Cartilaginous fishes have only one nostril on each side of the snout. However, each nostril is partly separated into 2 parts by a flap of skin, and actually water flows through the nostril just as in bony fishes.\n- Some bony fishes, the cichlids (discus, Jack Dempsey), have only one nostril on each side of the snout.
544046
they are called suckers on the ends of the tube feet.  they are controlled by the water-vascular system in echinoderms, such as starfish.  \n\ngood luck with the dissection!  i did it a few weeks ago...make sure to check out the two stomachs!!
616561
The scales- Same structure, shape, and composition- In fact, a related function, since sharks will brush the sides of their body by interesting possible food items to scrape off a little (of your skin, for example) in order to "taste" it with special sensors in the skin.  Generally, if a shark does this with a human, they will *not* attack further.
690872
To avoid attack by sharks, never swim with a bleeding wound, which sends them into a psychotic feeding-frenzy, keep nearer the beach and a constant vigil for them, with other swimmers, and preferably a very nearby boat, and as sharks nudge and nibble to determine if something is edible, you have to strike them hard -kick, punch, heel of hand, elbow- them on the nose, as they have a very sensitive area full of nerve-endings there, and can be fazed for a few minutes by a strong strike.\n  Bears are territorial, and 'own' a big area!  The worst thing to do is startle a bear, sneaking up on them.  You should sing while you hike, walk with jingle-bells on your boots, play a radio, makes a lot of noise, and they will hide, and watch you.  Never make eye-contact, never start running to escape, they can catch Olympic sprinters!  Keep  a big pistol to hand.  The noise will scare most off, but the gun helps gives you a confident psychic trace, that they pick up on, rather than you quaking in your boots, wishing you had a gun! \nBee-stings kill a lot more than both.
1015470
first, the idea that they don't "like how we taste" is just a theory. that is, it explains some observations but hasn't been empirically tested (for obvious reasons!). it's basically a hypothesis to cover why so many "bite-and-spit" attacks take place, where a shark briefly attacks a person and then swims away and leaves them there.\n\nnotably, however, there are other theories that cover this--for example, that plenty of bite-and-spit events are territorial warnings, or that this is a common feeding habit for some species where they bite, wait for the prey to weaken and die, and then return when there's not so much risk of retaliation and possible injury to the shark.\n\nif the "taste" theory is true, one major theory out there is that sharks have chemosensory capabilities to gauge how much fat is in prey. and let me tell you, we are a hell of a lot less fatty than a seal or sea lion. (obese though many of us may be, we don't need an insulating layer for constant coldwater diving.) so according to that theory, the shark would bite, realize the person isn't worth the effort, and go away.\n\nthis theory has really come in based on great white shark attacks, where bite-and-spit patterns seem fairly common in both human and natural prey (e.g. seal) situations. if they do this, and tiger or bull sharks don't, then there's probably an ecological reason for it, like where a white shark bites and backs off from a seal, whereas say a reef shark might bite as a territoriality or perceived threat thing.\n\nbut, bottom line, nobody knows, and any "expert theory"you hear is still a theory, even if it's from an expert.
23799
A Great White Shark will WIN because crocs can't swim as fast and sharks got way SHARPER teeth. There you go. SHARKS RULE THE SEA. But if its a land fight then OF course. The shark will be dead before you know it.
347164
YES! but that would depend on what species.\n\nsurprising to some, but NOT all sharks die when they stop moving. infact some species even tend to lie motionless at the bottom of underwater caves.\n\nCaribbean Reef Shark (Carcharhinus perezi)\nBanded Houndsharks (Triakis scyllium)\nWhitetip Reef Shark (Triaenodon obesus)\nLemon Sharks\nGrey Reef (Carcharhinus amblyrhynchos)\nBlackfin Reef (Carcharhinus melanopterus)\n\nare just a few examples.\n\nangel sharks lie motionless covered with sand on ocean floor to ambush prey.\nwhile some sharks "sleep"\n\nhope that helps :)
529180
They think it's other fish.  Light on fish scales resembles the same thing as shining on jewelry, etc.\n\nSo if you don't want to get chowed on by a shark, leave your jewelry at home, oh scaley one.
628912
Many kinds of sharks can be found in the waters off North Carolina. According to shark researcher Frank J. Schwartz, over 50 species of sharks are known to swim in the estuarine, shelf and deep ocean waters of North and South Carolina. 26 of those species are considered the most common sharks of North Carolina. \n\ntiger \nwhite-tip\nblue\nthesher\nsilky\natlantic sharpnose\nsmooth dogfish\nsand tiger\nspinner\nscalloped hammerhead\ngreat hammerhead\nbonnethead\nbull\nblacktip\nblacknose
884145
because they're not very good at this baddy thing. leave it to me ...  get me some sharks with freakin lasers attached to their heads!
181468
They could *be* shark teeth. There are plenty of places where you can pick them up right off the sand if you know where and how to look for them.