(i) _____can be used as industrial pollution indicators.
(ii) By the time of _____ mya, in vertebrates were formed and active
(iii) Jawless fish probably evolved around _____mya.
(iv) In 1938, a fish caught in south Africa happened to be a ______which was through to be extinct.
(v) The first mammals were the _____.
(vi) About_____mya, the dinosours suddenly disappeared from the earth.