Unlike their Cambrian ancestors, many of the Ordovician trilobites could roll themselves into balls at the approach of danger.

With this technique, Fortey's found about a 10:1 ratio for punctuated vs. gradual origins of species in Ordovician trilobites from Spitzbergen.

Using this technique for Ordovician trilobites from Spitzbergen, Fortey (1985) found a ratio of about 10:1 for cases of punctuation compared with gradualism.