In the film, Duke and Turk were originally the captain's dogs until the ship the Robinsons were on was chased by Kuala and his pirates into a storm and found itself stuck on rocks which weren't too far from land.
Francis Robinson, the youngest of the family, insisted they bring the two Great Danes with them to the island, despite Father Robinson's fears that they might sink the raft they rode on. But fortunately, they didn't sink their raft.
The following day, Duke and Turk help Mother Robinson search for Francis, who had found a baby elephant he named Rocky, while at the same time fending off the tiger that was on the island.
On the day of the Robinsons' holiday, Turk was one of the animals who participated in the race with Francis' monkey riding him, along with Rocky the elephant (who had Francis riding him), Lightning the donkey (who had Fritz riding him), Clementine the ostrich (who had Ernst Robinson riding her), and Duchess the zebra (who had Roberta riding her), while Duke stood with Mother and Father Robinson.
Trivia
Turk's muzzle is more black than Duke's and he has a white belly unlike Duke.
