Ursus maritimus tyrannus is an extinct subspecies of 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.Dating back to the Late Pleistocene, approximately 70,000 years ago, it is one of the oldest fossils assigned to the polar bear,however, recent reinvestigation of the fossil suggest brown bear affinities instead.