Kleefeld on Comics: On Strips: Animated B.C.
I did not realize before yesterday that Johnny Hart's B.C. had been animated multiple times. The first time was in 1973 (fifteen years after the strip debuted) when NBC aired B.C.: The First Thanksgiving and featured the talents of folks like Daws Butler and Don Messick. Peanuts had had success in animated holiday specials since A Charlie Brown Christmas first aired in 1965, and this B.C. special was presumably meant to compete against A Charlie Brown Thanksgiving which also first aired in 1973.
Curiously, a "sequel" (B.C.: A Special Christmas) didn't show up until 1981. It featured the voices of Bob Elliott and Ray Goulding this time. Johnny Hart is given full story credit here (he splits it with Jack Caprio on the Thanksgiving special), although the story is surprisingly secular given Hart's later penchant for proselytizing in his strip and how religious the Peanuts special was. The only real religious reference is a set of three men on camels walking off towards the North Star at the very end.
As near as I can tell, neither B.C. cartoon has seen wide syndication, nor have they been released on any form of home video. Evidently, they just didn't charm viewers in quite the same way Schulz's characters did. YouTube, however, does have the Christmas special as a single video, and it looks like there's enough clips of the Thanksgiving one to see that in it's entirety as well.