Cassidy was battling cancer at a San Jose assisted-living home when he died Thursday.
In a Facebook posting, Spirit bassist Mark Andes called Cassidy "one [of] the world's greatest drummers," The Hollywood Reporter said Sunday.
Cassidy was noted for his shaved head and performing drum solos with his bare hands. He earned the nickname "Mr. Skin," which was the title of a song on their 1970 album "Twelve Dreams of Dr. Sardonicus."
Ed and his stepson Randy California formed Spirit in Los Angeles and released their first album in 1968. Ed Cassidy, was 28 years older than his 16-year-old stepson -- born Randy Wolfe and given the California moniker by Jimi Hendrix -- and came from a jazz background.
The difference in ages and musical chops proved not to be a detriment to Spirit's success, the Reporter said. The group released 11 albums between 1968 and 1977 and several singles.
The group was also the headliner at Led Zepplin's first U.S. gig in 1968.