The New Cinema (1968)
A 30-minute unaired TV special on late-60s student films, with early Coppola and Lucas interviews.
The swashbuckling adventure of Captain Blood, written by Rafael Sabatini takes place in the town of Taunton. It was made into a film in 1935, starring Errol Flynn. Given Lucas's viewing habits, it's plausible he saw it and picked up the name of the rebellion's snow mounts from it.
Given the lack of an ocean around the above Taunton, it's probably not that Taunton in question; nevertheless that also exists. Who knows if it played some distant role?
Riders astride giant lizards might not have been an entirely novel concept by the mid 70s, but Ron Cobb's take on it had an air of the fantastic, while being grounded in reality. Cobb would go on to work on creatures for Star Wars , and this early design probably inspired the Dewback.