Rooli Revieu s how on any critet~ioii t h y t~oultl he i,nnked much 'liiglier' than elephants or hippopotami". h atoinical consideratioiis :inti karyotype stiiclics suggest that while the ~iiodern Cetacen are probably nionophylctic. thi, spemi whales iiiiglit Iiave diverged at a very early tinic. The probitbility of coiiinioti iincvstr-of till otlontocrtes C ' I I I ~ be discarded. "The earliest phase of cetacean radiation ;ippriirs to Ii;i-(. b w n c l o r e l ~ tirtl to (>-cnts involving the constriction imcl litter reopening of the \Vrstcrn 'I'ctliys Sea in tlie Lower Tertiary". Further radiat ;on seems to h a r e been associated with tlie c.ompletioii of tlir circiini-Xiitairtic ciirrent. changes in tlie tcmperaturc regimes in the 3Iitltllc Tertiary ant1 tlie interniittcnt ;ir-ailability of the Central -1merican seewav as a route of faiinal dispersul. As nn ;ippentlis to the cliapter on populations, GASKIZ; siinimarizes tlie estimittes of present popiiliition sizes of coiiinicrciiill~-rsploitetl Cet;ire;t, subdivided by regions. e. g. for Uitltrr/rtr u1y.dicefzc.v: 2200 in the \Vest Xniericiin a n d 30 '! in the East Americim Arctic and "Ion-tens to extinct ?" iii the European -iretic: for E u b n l u c m glncitrlis: 134