Tosefta על טהרות 2:8

There is a stringency with an olive's bulk from a corpse, which is that an olive's bulk from a corpse, an opening of a handbreadth [is enough to prevent the spreading of impurity], whereas [an entire] corpse [requires] an opening of four handbreadths [to prevent the spread of impurity] (see Oholot 3:6). Rabbi Natan says, one who possesses corpse-impurity can impart second-degree impurity, and can disqualify [terumah] at an additional degree (i.e., third-degree impurity, see Toh. 2:8).