Here are some clues:
1. For 250 years, this drawing was mistakenly credited to a German painter who specialized in animal paintings.
2. It is believed to date from around 1637 and was known as "the Braunschweig terrier."
3. Professor Thomas Doring from Germany said this about the drawing, "But the boldness of the strokes, the variations in the shading from very gentle to quite violent and the expressive gaze - these are very typical idiosyncrasies" of this artist's work.
4. Three leading scholars of this artist's drawings were "fully convinced" that the sketch was by him.
5. This dog is similar to the barking dog in the 1642 painting called 'The Night Watch', which hangs in the Rijksmuseum in the artist's native country.
Detail of the dog from "The Night Watch."
Famous masterpiece: "The Night Watch" from 1642.