Some of the most primitive organisms found in the fossil record are

Some of the most primitive organisms in these fossils are extinct. These already extinct organisms provide leeway of research for scientists to uncover what organisms roamed and came before what exists now. Also this provides evidence for the theory of evolution and how the mechanism, principles and processes that underlie this phenomenon has took place. Fossils are great finds in biological and evolutionary research in that they are one of the prominent evidence of how life came to be and the significant divergences of how environment has an effect to organisms’ survival. 

i'm guessing this is from edg enuity so the answers would be, from top to bottom,

theodor schwann

matthias schleiden

robert hooke

rudolph virchow

anton van leeuwenhoek