Children's picture book about a runaway dog that transforms into a creature with antlers

[Tori]

I checked this out from the library several times around 1987, so it's probably from either the 80's or 70's. It's a picture book with text about a boy and his pet dog who are best friends. Then the boy complains about the dog (I think he sees a pony and comments on how that would be a more fun pet to have) and the dog runs away into the woods. While in the woods, the dog gets transformed into a creature that's kind of a hodgepodge of different animals (I specifically remember that he gets antlers but I believe he also gets long legs like a horse or giraffe). At the end, the dog transforms back and goes home, where the boy is overjoyed to see him.

I remember really loving this as a small child but for the life of me, I cannot remember the title.

Thank you!

[Tori]

Nevermind, I found it. The Whingdingdilly by Bill Peet (1970). Brought up The Island of the Skog on amazon because I remembered that book having a similar feel to it, then clicked through the Customers Also Bought recommendations and there it was!