- "A sort of elephant." "With a trunk?" "Yes. Hairy all over." "Horrible?" ... "No. Gorgeous," said Titty hurriedly. (Titty and Bridget, SW7)
- "Don's as good a short for Mastodon as it is for Donald" (Daisy, SW20)
The Mastodon, actual name Don, is a member of a savage tribe, the Eels, and lives on Speedy, the hulk of a barge, half swallowed by the mud, in a creek between Mastodon Island (adjacent to Swallow Island) and the mainland. His family circumstances are not made explicit, but it seems that he is attached in some way to the natives at Witch's Quay.
- The Swallows and the Amazons meet the Mastodon in Secret Water. His splatchers leave big round marks on the mud, which Titty thinks are the marks of a Mastodon (a mammoth-like creature). When they meet him, and learn that his name is Don, Titty insists that this is short for Mastodon (SW8).
Mastodons feature in A Journey to the Centre of the Earth, a classic 1864 science fiction novel by Jules Verne. Titty and Dorothea have both read this book. When they go down the tunnel to consult Slater Bob, they hear a thudding noise. Dorothea asks Have you read "A Journey to the Centre of the Earth"? Titty replies About Hans Stek and the hot water spouting out of the rock? and Dorothea says About the mastodons ... it's a whole herd of them stamping (PP3).