Thomas was a sixth-round draft pick by the New England Patriots who was claimed by the Cowboys before the final preseason game. He was the fifth safety on the roster.
The addition of Toomer, a 2012 fifth-round pick by the Seattle Seahawks who has yet to play in an NFL regular-season game, gives the Cowboys seven linebackers on the roster.
The Cowboys waived safety Ahmad Dixon, a seventh-round pick out of Baylor, earlier Monday to make room for safety C.J. Spillman. Head coach Jason Garrett was noncommittal when asked whether the Cowboys plan to sign Dixon to the practice squad if he clears waivers.