It includes only 3 living species, and a number extinct fossil species.

In Protatlanta, however, a few additional fossil species have been described.

Several fossil species which became extinct long ago are also known.

Several fossil species have been identified, including one from Africa.

Figure 7.1 illustrates the very obvious way in which a new fossil species may seem to be diachronous.

Large fossil species (very different from any living forms) are found in the Carboniferous formation.

To prove this, all living specimens must belong to the same fossil species.

The living specimens need not belong to the same fossil species (or even genus).

Several fossil species are known, including two extinct families.

Almost 200 species have been described, and 11 fossil species are known.