My girlfriend is always disappointed when I do these lungfish strips, she claims that they are "too sad." When I keep them alive, it's just so I can torture them more later. I cannot really deny it.
I've been wanting to include an ammonite in the comic since it started! When doing "research" on fossils these little guys always turn up eventually. Ammonites of one kind or another were alive all the way up until the K-T extinction event, and people who really know their rocks can, I'm told, often identify what geologic layer a rock is from based on fossil ammonites in it alone.