 Other synonyms of "M. ferox" include "Aelurocyon brevifacies", "Brachypsalis simplicidens" and "Paroligobunis simplicidens".Specimens of "M. ferox" have been found at ten sites in South Dakota, Nebraska and Wyoming, dated to the Harrisonian period - from 24.8 to 20.6 million years ago.The 19 specimens so far identified have a wide range of sizes, which is believed to be evidence of extreme sexual dimorphism, a phenomenon where males and females of the species will grow to different sizes; a 1996 study rejected the possibility of multiple "morphologically uniform" but differently sized species as unlikely.