"Fritz the Cat" was the first animated film to receive an X rating from the MPAA, and is the highest grossing independent animated film of all time. With the success of his second film, "Heavy Traffic", Bakshi became the first person in the animation industry since Walt Disney to have two financially successful films released back-to-back. A few attempts were made to produce independent feature-length animated films in the 1970s. Several of these were decidedly adult-oriented productions from outside the United States, including the Canadian "Heavy Metal," the English "Watership Down" and a live-action/animated version of the Pink Floyd concept album "The Wall", all of which received wide release in the United States. Other films like Richard Williams' "" were less successful. The industry largely continued to ignore or dismiss animation as something only kids watched on Saturday morning television. A notable exception was a series of films based on the "Peanuts" franchise, beginning with the 1969 film "A Boy Named Charlie Brown", which was both a commercial and critical success; the films were made with the same production team behind the acclaimed "Peanuts" television specials that were airing throughout the time period, led by Bill Melendez. Animation on television focused almost exclusively on children, and the tradition of getting up early to watch Saturday morning cartoons became a weekly ritual for millions of American kids. The networks were glad to oblige their demands by providing hours-long blocks of cartoon shows. Hanna-Barbera Productions became the leader in the production of TV cartoons for children. A number of other studios produced TV cartoons, such as Filmation ("Fat Albert and the Cosby Kids", "The Archies") and DePatie-Freleng Enterprises ("The Pink Panther"), but Hanna-Barbera had developed a virtual lock on Saturday morning cartoons by the 1970s. Such critics of Hanna-Barbera's style of limited animation as Chuck Jones referred to it disparagingly as "illustrated radio," yet when one show was cancelled, the studio usually had another one ready to replace it because they were so cheap to produce. From the late 1960s through the early 1980s, several successful prime-time animated TV specials aired. Because these one-shot cartoons were aired during prime-time hours (and thus had to appeal to adults as well as children), they had to obtain higher ratings than their Saturday and weekday counterparts. CBS in particular allowed a large number of animated TV specials to air on its network, and several of these continue to be repeated annually and sold on video and DVD.