Ursus abstrusus was a small primitive black bear with a long, narrow skull. It is recognized as the first Ursus to have been present in North America. Early immigration of Ursus from the Old World is supported by fossils found in White Bluffs, Washington and Hagerman, Idaho (both dated at about 4.3 MYA). Fossils have also been found on Pine Nut Mountains near Carson City, Nevada and dated as far back as 4.95 + 0.02 MYA.

Ursus abstrusus was closely related to the Auvergne Bear (Ursus minimus) and is believed by some to have given rise to the European Cave Bear (Ursus spelaeus), the American Black Bear (Ursus americanus), and the Asiatic Black Bear (Ursus thibetanus).

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