A date of 4300 +/- 90 BP for extinct megafauna in Argentina is discussed. T
he fossil remains come from the Guerrero Member (area) of the Lujan Formati
on near the city of Lujan, Buenos Aires Province. The age of the top of the
Guerrero Member is constrained by more than 60 radiocarbon dates obtained
from the overlying Rio Salado Member of Lujan Formation, Las Escobas Format
ion, and Puesto Callejon Viejo Soil, most of them older than 4300 BP. In vi
ew of its low collagen content, the C-14 measurement of bone sample from Lu
jan should not be accepted uncritically. Because of the poor bone preservat
ion and the possible introduction of "young" contaminants that were not com
pletely eliminated, the C-14 date of 4300 +/- 90 BP is not reliable. Both b
iostratigraphic and C-14 dating evidence indicates that the date of 4300 BP
for the last representative of extinct megafauna in South America is unsup
ported.