Have you ever seen a unique fossil that has helped find information of things that we knew little about?

Question: Have you ever seen a unique fossil that has helped find information of things that we knew little about?

Asked by ishy to Duncan on 24 Mar 2010 in Categories: Test methods.
- Duncan Murdock answered on 24 Mar 2010:
  
  I was lucky enough to see the complete fossil of a very old fish known as a conodont (there’s only 11 in the world). They have tiny teeth in their mouth but no other bones, and before these fossils were found no-one knew what the teeth belonged to.

Question: Have you ever seen a unique fossil that has helped find information of things that we knew little about?