if you scroll down to part C, it gives the citations to the works referenced in the data.
However, these data are quite old. You might want to check one of the more recent mammal data databases, either the updated EltonTraits1 (now TetrapodTraits) or
COMBINE (Metadata S1. Soria, C.D., Pacifici, M. Di Marco, M. Stephen, S.M., and C. Rondinini. 2021. COMBINE: a coalesced mammal database of intrinsic and extrinsic traits. Ecology.