Who is Toto? How can you tell?

Toto is Dorothy’s dog in the novel and film The Wonderful Wizard of Oz. Early in the book, we are presented with Dorothy and her small dog. As it states on page 10 of the book, Toto is “a little black dog, with long, silky hair and small black eyes that twinkled merrily on either side of his funny, wee nose.”
Toto is Dorothy’s closest companion throughout the story, being the only individual who comes along to the land of Oz with her. It is a good assumption that Toto is a miniature schnauzer or some similar breed of dog based on the description, which is accurately portrayed in the original film. Toto acts as an extension of Dorothy at times, such as when he fights or bites her enemies for her when she is unable to fight. Toto also reveals the identity of the Wizard of Oz by pulling back the curtain behind which he is hiding.