28. The diagram below shows the abundance of organisms called crinoids, blastoids and echinoids, during different geologic periods. The number of species living at any given time is represented by the width of the blackened areas.

Which statement about crinoids, blastoids and echinoids is best supported by the diagram?

A) They are now extinct

B) They came into existence during the same geologic period

C) They existed during the Devonian period

D) They have steadily increased in number since they first appeared

Correct Answer: Option C - They existed during the Devonian period

The diagram above shows existence of all the 3 organisms – crinoids, blastoids and echinoids in the Devonian period which is a subperiod of the Paleozoic era.

Incorrect Options

Only blastoids are now extinct. Hence, option A is incorrect.

Crinoids came into existence in the ordovician period; Blastoids and Echinoids came into existence in the Silurian period. Hence, option B is incorrect.

Crinoids, blastoids and echinoids have increased in number vastly in the Mississippian period, which does not represent a gradual increase in population. Hence, option D is incorrect.