Pat Boone didn't want to make this film but was talked into it by his agent. Years later he stated he's glad he did it because of the regular residual checks it brings in and because it's the movie he'll probably be best remembered for.
The "Dimetrodons" in the movie were played by a large type of lizard called a rhinoceros iguana. It is about 3-6 ft. long and is kept as a pet in many places. Dimetrodon in real life was a type of Synapsid reptile. It reached about 12 feet in size, and lived in Western North America.
The professor's name in the original novel (French language) was Otto Lidenbrock, a German. In the movie it was changed to Oliver Lindenbrook, a Scotsman. The name of his assistant Axel was Caledonized into Alec. (This was done because of historical hindsight, as 19th-century Scots had become known as the best field geologists, with Germans preferring lab-bound geology.) A more drastic change had already been made with the first (anonymous) English translation of the novel when the Professor's surname became Hartwig and Axel became an English student named Henry Lawson.
James Mason replaced an ailing Clifton Webb in the part of Professor Lindenbrook before filming began. Alexander Scourby started shooting at Carlsbad Caverns in the Count Saknussemm role, but the producers were unhappy with him and he was replaced with Thayer David.
Gertrude was supposed to be an Eider duck from Canada but Ralph Helfer couldn't get one into the United States because the USDA insisted that a permit be issued before one could enter so he decided to make his own Eider duck.
While Alec is lost, he travels through awesome studio sets, well lit for dramatic effect. In reality, Alec's attempt to find his way back by the light of a single coil lamp would have been a deadly, nightmarish experience.