 Complete the following phrase:  The Tremarctinae or short-faced bears is a subfamily of Ursidae that contains one living representative, the spectacled bear Tremarctos ornatus of South America, and several extinct species from four genera: the Florida spectacled bear Tremarctos floridanus, the North American short-faced bears of genera Plionarctos P. edensis and P. harroldorum and Arctodus A. pristinus and A. simus, and the South American giant short-faced bears of Arctotherium including A. angustidens, A. vetustum, A. bonariense, A. wingei, and A. tarijense. The group is thought to have originated in eastern North America, and then invaded South America as part of the 