In 1980 geologist Juan Carlos Sciutto discovered a rich fossil site six kilometres north of the Ocho Hermanos ranch in
Chubut province. Among the fossils found there were some theropod remains. Later, a team led by Argentinian
paleontologist José Fernando Bonaparte recovered some more theropod bones, possibly from the same individual. In 1986, Rubén Martínez, Olga Giménez, Jorge Rodríguez and Graciela Bochatey described the theropod fossils and coined the genus and species
Xenotarsosaurus bonapartei for them. The generic name is derived from
Greek xenos, "strange",
tarsos, "
tarsus", and
sauros, "lizard", a reference to the exceptional build of the ankle. The
specific name bonapartei honours Bonaparte. The
type specimens (and only known fossils of
Xenotarsosaurus) were found in the
Bajo Barreal Formation. In 1986 this formation was seen as
Campanian; today it is thought to date to the earlier
Cenomanian–
Turonian. The bones consist of two
cotypes: UNPSJB PV 184, a series of two anterior dorsal
vertebrae, and PVL 612, a right hind limb including the long
femur, the
tibia,
fibula and astragalocalcaneum of the ankle. The exceptional complete fusion, without
sutures, of the
astragalus and
calcaneum, forming an element that is again fused to the widened lower end of the tibia, occasioned the generic name. ==Description==