If this is indeed a Paulus Roetter painting, it is a very different style from most of his other works.  It was found in a portfolio that contained other Paulus Roetter artwork and the style of the lion's face is very similar to pencil sketches that he drew in the 1880s of a dog and, especially, an orangutan and cat.  The 1880 U.S. census said that he had rheumatism which can also explain the style difference.