Peter, Paul and Mary bassist Dick Kniss has died at age 74.

The New York Times reports that Kniss died of chronic obstructive pulmonary disease in Kingston New York on Wednesday.

Kniss played with the folk trio for forty years and was considered a fourth member. He also worked with singer-songwriter John Denver and co-wrote Denver's classic “Sunshine on My Shoulders” (Denver, incidentally, wrote Peter Paul and Mary's classic, "Leaving on a Jet Plane").

Kniss started out as a jazz sideman and joined Peter Yarrow, Paul Stookey and Mary Travers in 1964. They split up in 1970 and Kniss went to work with Denver. Then, when Peter, Paul and Mary reunited eight years later, Kniss rejoined the group and played with them until Mary Travers' death in 2009.

Peter Yarrow said in a statement - via Billboard - that Kniss was "our intrepid bass player for almost as long as we performed together.

 "He was a dear and beloved part of our closest family circle and his bass playing was always a great fourth voice in our music as well as, conceptually, an original and delightfully surprising new statement added to our vocal arrangements."

Kniss is survived by his wife Diane, their two sons, a son from a previous relationship, two sisters, and seven grandchildren.