I studied geology as an undergraduate, lo these many many years ago. I liked life, but blood and guts made me queasy, so clearly what was required was ossified life! Fossils were the perfect form of life for me to study; not squishy, not smelly, mostly rock, and yet still retaining the flourishes that life is famous for. It all made me very happy, until I graduated into the Reagan budget cuts, and only oil companies were hiring geologists. So I went to grad school and studied maps instead, and had another, different happy life instead. But fossils still make me absurdly happy.
Trilobites are entirely extinct, even though pill bugs look like them. It was a great parenting moment when Alice looked at the scuttling pillbugs under the climbing thing in the backyard and asked if they were trilobites. Sadly, no, but good guess.
Yesterday's circle was made but flickr was misbehaving, so you'll have to look for it there.