HYAENODON VENTURAE (HYAENODONTIDAE, CREODONTA, MAMMALIA) FROM THE EARLY CHADRONIAN (LATEST EOCENE) OF WYOMING

Two new specimens of Hyaenodon venturae from the early Chadronian (lat est Eocene) of Wyoming provide new information about this rare, miniat ure hyaenodont, and extend the upper end of the temporal range of the species. The significant difference between H. venturae and H. microdo n, the two smallest North American species of Hyaenodon, is the absenc e of synostosis of the mandibular symphysis in adult H. venturae. In H yaenodon microdon, from the middle Chadronian, on the contrary, fusion of the symphysis is complete while the individual is still in the juv enile stage of ontogenesis, before the eruption of m3. Within the genu s Hyaenodon the mi becomes relatively smaller as the length of the too th row (p1-m3) increases; this relationship can be demonstrated in the series of species from the miniature H. venturae to the giant H. mega loides.