JFS says animals are created spiritually in heaven.
Joseph F. Smith, Doctrines of Salvation, 3 vols. (Salt Lake City: Bookcraft, 1956), 1:47
While it is true that all things were created spiritually, or as spirits, before they were naturally upon the face of the earth, this creation, we are informed, was in heaven. This applies to animals of all descriptions and also to plant life, before there was flesh upon the earth, or in the water, or in the air.