Ursus maritimus tyrannus

Ursus maritimus tyrannus (lit. 'tyrant maritime bear') is a controversial extinct subspecies of polar bear.

Discovery
The subspecies of polar bear was named by the Finnish paleontologist Björn Kurtén in 1964, based on a single fragmentary ulna found in the gravels of the Thames at Kew Bridge, London. The fossil was also discovered alongside steppe bison (Bison priscus). reindeer (Rangifer tarandus) and wolves (Canis lupus).

The specimen is interpreted to represent a relatively large subadult individual. The ulna is estimated to have been 48.5 cm long when complete- for comparison, modern subadult polar bear ulnae are 36 - 43 cm long. The ulna was dated to the early Weichselian of the Late Pleistocene (~70kya). Of the 16 specimens identified as Pleistocene polar bears, this is the only fossil ascribed to this subspecies.

Controversy
In 2008 Charles Harington stated that the identification of a polar bear is plausible based on sea level changes and ice conditions in the North Sea of the time period. However he also noted that Andy Currant of the Natural History Museum, London believes that fossil represents a huge brown bear rather than a polar bear, as fauna assemblages from other contemporary British sites, also dominated by steppe bison, reindeer and wolves, preserve gigantic brown bears like the Kew Bridge bear.

Andy Currant's opinion that the Kew Bridge fossil belongs to a brown bear, although referred to in a 2007 BBC interview and in studies from 2009 and 2022, awaits scientific verification.