CBS says Scott Pelley is out as “CBS Evening News” anchor after six years in the role, and network veteran Anthony Mason will fill in temporarily as a search for a new anchor begins.

The network announced Wednesday that Pelley will return to work full-time at the network’s flagship newsmagazine “60 Minutes” as it begins its 50th anniversary season.

CBS gave no reason publicly for ousting Pelley. CBS’ evening newscast is a distant third in the competition with ABC and NBC, and lately has seen some further ratings slippage.

News of his departure broke unexpectedly Tuesday night, when reports spread of Pelley’s office at the evening newscast being cleaned out.