Ursus maritimus tyrannus is an extinct subspecies of polar bear, known from a single fragmentary ulna found in the gravels of the Thames at Kew Bridge, London. It was named by the Finnish paleontologist Björn Kurtén in 1964 and is interpreted to represent a relatively large subadult individual: the ulna is estimated to have been 48.5 cm (19 in) long when complete, "the longest ursine ulna on record".[1] Dating back to the Late Pleistocene, approximately 70,000 years ago, it is the oldest fossil assigned to the polar bear;[2] however, an unpublished reinvestigation of the fossil suggest brown bear affinities.[3]