The stromatolite (p. 523) comes from a time before the appearance of eukaryotes, much less truly multicellular organisms. While its cells work together to form a pillow-like structure, each is an independent organism. In contrast, today we still have such things as stomatolites but we also have eukaryotes, including large and complex ones in which the cells are part of the whole.
Work Step by Step
This is a question with many possible answers. Scan through Concept 25.2 and pick one of the many examples. Use your imagination to think about life today (where it is,how big it is, etc.) and compare to what the world represented by your chosen fossil was like.