Story, first published: Dark Forces (1980)
The story has a Lovecraftian flavor - a writer, investigating his genealogy, returns to his ancestral New England dwelling shunned by the local residents because of a well which makes whistling sounds. He sees loathsome shapes near the well which turn out to be intelligent dinosaurs who remind him that he is their "brother." Simak managed to work in two of his favorite science-fiction themes into what is supposedly a horror tale, dinosaurs with intelligence and the brotherhood of intelligent life.
Ewald, Robert J.: When the Fires Burn High and the Wind is from the North, p.126