Unlike most of its relatives, such as Proborhyaena and Arminiheringia, Callistoe had a narrow, puny snout, and the shape of its skull resembled that of a thylacine.

Callistoe vincei was first described in 2002, based on an almost complete and exceptionally preserved skeleton from the Lumbrera Formation, in the Salta Province of Argentina.

Callistoe was a member of the family Proborhyaenidae, a clade of Sparassodonts typical of the Early Cenozoic, usually large-sized and with a robust build.

Argot & Babot described in 2011 very long and slightly curved claws, quite different from those of other sparassodonts; their shape suggesting an ability to dig.

As it lived during the Early Eocene, it may be one of the first examples of a predatory mammal with fossorial habits, millions of years before the rise of the first burrowing mustelidae on other continents.