ABSTRACT
Theabsoluteageofsomeofthesecreaturescannowbeascertainedasaconsequenceofrefinementsinthemeasurement ofradioactivity(potassium/argonorK/A)insomeconstituent mineralsofvolcanicrocks.Theirtemporalrangeextendsback nearlytwomillionyearswithsomerepresentativesapparently havingpersisteduntillessthanamillionyearsago.Theirdiscoveryhasthereforetripledthetimerangepreviouslyknown fortheevolutionofthehominids.
