Dorothy's little dog in L. Frank Baum's The Wonderful Wizard of Oz is described as a black dog, with long, silky hair. The illustrator W.W. Denslow made him look like a disheveled terrier or Scottie. Later editions illustrated by John R. Neill redrew Toto as a Boston bull. For the MGM movie, Scotties were considered but a Cairn terrier named Terry eventually landed the role.

SOURCE:
Tremain, Ruthven. The Animals' Who's Who. New York: Charles
Scribner's Sons, 1982.