For many years as part of my school visits, I've made drawings for my audiences that show how I love to have fun with dinosaurs and fun with words.
For example, I draw a triceratops and ask my audience if they could guess what it is riding on. My completed drawing is this three-horned dinosaur riding on a three-wheeler... A triceratops on a tricycle.
One day the words "trio of triceratops" popped into my head along with a visual of a trio of triceratops on tricycles. I grabbed a pad and pen and began jotting down lines: A trio of triceratops touching their toes. A trio of triceratops trying on trousers. A trio of triceratops tasting tangerines, etc.
I sent a list to my editor at Harcourt, Diane D'Andrade, along with my visual of a trio of triceratops on tricycles. She loved it so much she suggested doing a companion book with "a pair of _________," which turned out to be A Pair of Protoceratops.