This cartoon was by regular Playboy cartoonist Dink (Leo) Siegel (1910-2003) and appeared in the November 1964 issue. Oddly, it's quite hard to find any information about him on the net other than that he was born in Birmingham, Alabama. He worked for many other magazines as well as Playboy (for whom he contributed for over 25 years) including Good Houskeeping, Life, Cosmopolitan and the Saturday Evening Post.
Much prehistoric fiction (such as Jean M Auel's books) feature inter-action between early Homo Sapiens and Neanderthals and no doubt this was the inspiration for this cartoon. Or not. Anyway, the cavegirl dinosaur co-existence pre-dates One Million Years BC by two years.