A new biostratigraphic correlation is suggested for the Palaeocene–Eocene boundary strata in the Holarctic. Great significance is attached to the Thanetian hiatus which has critical importance in the placing of the Palaeocene–Eocene boundary in Western Europe. Intercontinental correlation of the Palaeocene–Eocene boundary in non-marine strata by means of mammals reveals the duration of the Thanetian hiatus in the Paris Basin. It corresponds almost entirely to the Clarkforkian Land Mammal Age of North America and possibly to the Zhigden and Naran Members of the Naran-Bulak Formation of Mongolia, which suggests a Palaeocene age for the Clark's Fork fauna. The Gray Bull and Bumban faunas appear to be practically contemporaneous and are correlated with the Sparnacian fauna of West European Meudon. The Palaeocene–Eocene boundary in North America is thus traced beneath the Gray Bull zone (Wasatchian Land Mammal Age), while in Central Asia it is believed to underlie the Bumban Member of the Naran-Bulak sections where there is evidence of the simultaneous appearance of perissodactyls, primates (Omomyidae), rodents, condylarths of the genus Hyopsodus and others.