Procoptodon goliah, the largest macropodid known to have existed, was a sthenurine kangaroo, but sthenurines occurred in a range of sizes, with Procoptodon gilli being the smallest at the size of a small wallaby.
The text describes Procoptodon goliah as the largest known macropodid and explains that sthenurines are a diverse group with varying sizes.  Procoptodon gilli is mentioned as the smallest member of this family, comparable in size to a small wallaby.