Pterodactyls appear multiple times in Calvin and Hobbes. They are often featured in Calvin's dinosaur fantasies, and a pterodactyl was an important plot point in the first Transmogrifier Gun story arc.
Alter Ego
A pteranodon also appeared as a minor alter ego of Calvin's. He appeared in a single Sunday strip, where Calvin read his dinosaur book and enacted a pteranodon fantasy by dressing up as one and jumping off the roof of his house.
Transmogrifier Gun Alter Egos
Calvin also appeared as a ptrodactyl in among the Transmogrifier Gun Alter Egos of the first Transmogrifier Gun story arc (2/8 through 2/20 1988).