What it was
A hand-sized fish, fourteen and a half centimeters at most. A single flat spine rises behind its head and curves forward over its own skull. Think of a fishing rod bent above its eyes.
Only the males
Only the males carry the spine. Where these fossils come from, males heavily outnumber females, and one slab seems to catch a pair together. One slab is a hint, not a finding.
Where it was found
A quarry in Montana called Bear Gulch, a shallow tropical bay that turned to fine limestone about 324 million years ago. The quarry has given up more than 5,000 fish.