J.D. Souther, a pivotal figure in the Southern California country-rock movement of the 1970s and a prolific songwriter for the Eagles and Linda Ronstadt, has died at the age of 78 at his home in New Mexico. Souther co-wrote some of the Eagles' most iconic songs, including 'New Kid in Town', 'Heartache Tonight', and 'Best of My Love', and had a successful solo career with hits like 'You're Only Lonely'. He also wrote for artists such as James Taylor, Bonnie Raitt, Dixie Chicks, and George Strait. Souther was scheduled to begin a tour in Phoenix next week and had recently performed with the Eagles in January. His contributions extended beyond music into acting, with roles in TV shows like 'Nashville' and 'Thirtysomething' and films such as 'My Girl 2'. His death was confirmed by a representative for the Eagles, but no cause was given.