Question

Protozoans are abundant during Phanerozoic, but absent in the Proterozoic fossil record. What is the likely cause for this difference?

Select one:
a. Proterozoic protozoans were likely very large.
b. Proterozoic protozoans had shells.
c. Proterozoic protozoans were much smaller.
d. Proterozoic protozoans were likely shell-less

Answer 1

The absence of protozoans in the Proterozoic fossil record is likely because Proterozoic protozoans were shell-less.

Step-by-step explanation:

The likely cause for the absence of protozoans in the Proterozoic fossil record is that Proterozoic protozoans were likely shell-less.

Protozoans are diverse single-celled organisms that can be free-living or parasitic. Fossil evidence suggests that protozoans were not present in the Proterozoic era, which spans from 2.5 billion to 541 million years ago. This could be due to the absence of fossils, as shell-less protozoans would have left behind fewer durable remains compared to shell-bearing organisms like trilobites.