Meanings of ordovician trilobites in English

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.