In his final year, he was moved to a backup role behind John Thiede, on a team that finished with a record of 1–8–2.
[1] Thornton was selected by the Dallas Cowboys in the eighth round (219th overall) of the 1979 NFL draft, after dropping because of his diminished production as a college senior.
As a rookie, he helped to compensate the loss of Ed "Too Tall" Jones to his boxing retirement, by coming on passing downs in place of Larry Cole at left defensive end and unofficially finishing second on the team with 6 sacks.
[3] In 1980, the return of Jones reduced his playing time, unofficially posting 3 sacks, including one against Vince Ferragamo in the NFC Wild Card Game.
[9] On March 28, 1984, he was traded to the Denver Gold in exchange for linebacker Bob Knapton and an undisclosed 1985 draft choice.