Page 226 - The Evolution Impasse 2

224 Trilobites

event dur ing the en tire his to ry of the
Metazoa, the Cambrian ex plo sion es -
tab lished vir tu al ly all the ma jor an i mal
body forms—Bauplane or phy la—that
would ex ist there aft er, in clud ing many
that were "weed ed out" and be came
ex tinct. Compared with the 30 or so
ex tant phy la, some peo ple es ti mate that
the Cambrian ex plo sion may have gen -
er at ed as many as 100. 260

TRILOBITES

Trilobites are one of the most in -
ter est ing liv ing groups that sud den -
ly emerged in the Cambrian Period
and sub se quent ly be came ex tinct.
They be long to the phy lum
Arthropoda, and are very com plex
crea tures with hard shells, seg ment -
ed bod ies and com plex or gans. The
fos sil rec ords have al lowed a great
The im ag i nary tree of life drawn up by the
deal of in for ma tion to be ob tained
ev o lu tion ist bi ol o gist Ernst Haeckel in
1866. re gard ing the tri lo bite eye. It con sist -
ed of scores of ti ny cells, each of
Some of these phy la then be came ex - which con tains a pair of len ses. This
tinct in the pe ri od that fol lowed, and eye struc ture is a mar vel of cre a tion.
on ly a few phy la have sur vived Richard Fortey, an ev o lu tion ist
down to the present day. pa le on tol o gist from London's
The well-known ev o lu tion ist pa - Natural History Museum, says this
le on tol o gist Roger Lewin re fers to about the ex traor di na ry num ber of
this ex traor di na ry state of af fairs len ses pos sessed by some tri lo bites:
that de mol ish es all the as sump tions
One of the most dif fi cult jobs I ev er at -
of Darwinism: tempt ed was to count the num ber of
The most im por tant ev o lu tion a ry len ses in a large tri lo bite eye. I took

The Evolution Impasse II