Page 120 - The Evolution Impasse 2

118 Origin of the Marine Mammals

depths, and ma rine cur rents. The more im por tant to them. Vision re -
crea ture's eyes are po si tioned on the quires light, but many whales and
sides of the head in or der to avoid dol phins hunt in dark re gions un der
di rect con tact with the cur rent. the sea thanks to a kind of nat u ral
In ad di tion, ma rine mam mals so nar. Toothed whales in par tic u lar
have a hard lay er to pro tect the eye are able to "see" by means of the
dur ing deep dives. Since there is in - sound waves re turn ing to them,
creas ing dark ness be neath a depth of much as a bat can. Sound waves are
9 me ters (29 feet), the mam mals' eyes fo cused and sent to one point. The
have been equipped with a num ber re turn ing waves are then an a lyzed
of fea tures that en a ble them to adapt and in ter pret ed in the an i mal's
to such a dark en vi ron ment. The lens brain. This anal y sis quite clear ly
is spher i cal. There are many more gives the shape, size, speed and po -
light-sen si tive rod cells than cone si tion of an ob ject. These an i mals' so -
cells, which are sen si tive to col or nar sys tem is ex ceed ing ly sen si tive.
and de tail. Moreover, the eye has a Dolphins, for ex am ple, can de tect a
spe cial lay er con tain ing phos pho rus. per son's in side div ing in to the wa -
For these rea sons, ma rine mam mals ter. They use sound waves for com -
can see very well in dark en vi ron - mu ni ca tion as well as for di rec tion-
ments. find ing. Two whales hun dreds of
Then again, sight is not ma rine kil o me ters apart can com mu ni cate
mam mals' pri ma ry sense. Unlike by the use of sound.
land mam mals, hear ing is much How do these an i mals pro duce