英语时差:锤头鲨的锤头2
The Hammerhead’s Hammerhead These unique sharks have heads resembling flattened, T shaped hammers. But how would such a weird head evolve? One hypothesis is that having their eyes spaced far apart might give these sharks better 3D vision. Another hypothesis is that sharks use the hammerhead literally, smashing it against the ocean floor to stir up prey. But both of these hypotheses have been ruled out experimentally. The hammer head may improve the sharks’ maneuverability and stability in the water, but more studies are needed to know if or how the hammer shape improves the sharks’ swimming abilities. What else could explain the hammer shape? It may have to do with electricity! All sharks have a special sensory system to detect weak electrical fields emitted by all marine animals. Sharks use this electro sense to find hidden or camouflaged prey. Researchers at the University of Hawaii found that hammerhead sharks have more electrosensory pores per surface area than other sharks do. In addition to higher pore density, their wide head gives hammerheads a larger search. In tests, hammerheads were better able to find buried artificial electrical targets using the electroreceptors in their wide heads than non hammerhead sharks were. It’s sort of like scanning the beach with a metal detector. If the diameter of your metal detector was bigger than that of your friend’s, you’d have the advantage since you could cover more area faster than she could. Like with a larger metal detector, the wide flat hammer shaped head might allow hammerheads to scan for prey more efficiently than their competitors.
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