Graptolites are strange little creatures that flourished during the Palaeozoic. They get their name from looking like writing in the rock. They appear to have evolved backward: The earliest are complex nets with many branches (stipes) and crosslinks. As time passes the complexity decreases until the last examples are just single stipe.
The specimen above contains many examples of Monograptus colonus. The magnification shows more detail: The jagged edge formed a series of cups each with its own zooid.