I think it was more like 1972 or so when Dennis did the first part of River Song, but I could be wrong.
My source for the 1970 date is Andrew G. Doe, who says "The opening piano riff, representing the flow of the river, dates back to the 1970 sessions."
http://www.angelfire.com/la/Beachboysbritain/AGDPOB.htmlCorrect - it was part of a longer piece called "Ecology". The piano riff definitely pre-dated "Tiny Dancer". That said, I think the similarity is purely coincidental.