The mode or how fast species evolve is a question that has been discussed for decades. Darwin felt that organisms need not evolve at any particular rate. Some could evolve slowly whereas others could evolve quickly.  Two examples illustration the differences are shown below.  First are two brachiopod species with the bottom pair from the Ordovician and the top pair from the Silurian.

The second example is a relative of the oyster.  The smaller bottom shell is from the Jurassic and the larger top shell is from the Cretaceous.  Both the brachiopods and the oysters examples show changes that occurred between 7 and 10 million years.  Which one shows more evolutionary change in the 7-10 million years, the brachiopods or the oysters?