What is the epic song of a group?

War - All Day Music
Johnny Guitar Watson - A Real Mother For You
Bruce Hornsby - The Way It Is
Elton John - Levon
Randy Crawford - Knockin' On Heaven's Door
Stanley Clarke - East River Drive
Brad Mehldau - Since I Fell For You
The Crusaders - Hard Times

Gene Clark - Strength of Strings
Pink Floyd - Echoes
Neil Young - Cortez the Killer

Roberjerman it’s “The Byrds”, not “The Byrd’s”. 

Elton John, “Burn Down the Mission”
Billy Joel, “We Didn’t Start the Fire”
and +1 for the Beatles, “A Day In The Life”

In no particular order....
Eagles - Hotel California
Molly Hatchet- Gator Country
Skynyrd- Free Bird
Patsy Cline - Crazy
Paul Simon - Late in the Evening
Frank Sinatra - That's Life
David Bromberg - Cocaine Blues
Linda Ronstadt - Long Long Time
Stuff - Do You Want Some of This?
Doc Watson - Sadie
Eris Clapton - Layla
New Grass Revival - Lee Highway Blues
Bobby Bland - Stormy Monday Blues
Temptations - My Girl
Wilson Pickett - Mustang Sally
Elton John- Take Me to the Pilot