Daniel O'Brien, 43, of Orchard Drive, Cottenham, Cambridge, had admitted the robbery and driving a getaway vehicle, and was sentenced to 16 months in prison when he appeared at Nottingham Crown Court on February 17.
He was one of two men who arranged to meet the dealer in the car park of a McDonald's restaurant in Newark on June 11, 2011, with a view to buying the horn, said to be worth about £20,000.
Last year, his accomplice Michael Kealy, 27, of Abbeylands, Askeaton, Co Limerick, was found guilty of robbery by joint enterprise, extradited from Ireland, and sentenced to prison.
The meeting had been set up via another antiques dealer who had put the victim in contact with the pair. When a scuffle broke out and the pair made off with the horn, the dealer clung to their vehicle. He was thrown to the ground, suffering bruising to the brain, cuts and a fractured wrist which required several weeks of treatment.
Kealy was arrested in 2011 while attempting to board a ferry in Harwich, Essex. O'Brien was arrested in Cambridge but then fled and was re-arrested after European law enforcement agency EuroPol traced him to Alicante Airport in October 2013.