186 Evolution? The Fossils Say YES!
Let us look at some of many examples of evolution in the well-studied forams first. One
of the classic examples of long-term evolution in the foraminifera is provided by a group
known as the Fusulinidae (fig. 8.3). Fusulinids were benthic (bottom-dwelling) foraminifera,
so they were not constrained to be tiny and float in the plankton. Instead, they secreted
shells that ranged from the size of a grain of rice up to 5 centimeters (2 inches) long, which
is enormous for a single-celled organism. Like many modern large benthic foraminifera,
fusulinids probably harbored symbiotic algae within their tissues to enable them to grow so
FIGURE 8.2. Examples of common groups of planktonic microfossils. (A) A foraminiferan, showing the bubble-
shaped chambers made of calcite surrounded by long fingers of protoplasm known as pseudopodia. (Courtesy
J. Kennett) (B) A radiolarian, with its characteristic porous spiny shell made of silica. (From Haq and Boersma
1978) (C) A diatom, with its perforated petri dish–shaped shells made of silica. (Courtesy J. Barron) (D) A
coccolithophorid alga, surrounded by multiple plates (coccoliths) made of calcite. (Courtesy W. Siesser)
(A) (B)
(C) (D)