DUBAI (Reuters) - Dubai's Emirates announced an order for 50 additional Airbus A380 superjumbos on Sunday, minutes after placing a record order for 150 Boeing jets at the opening of the Dubai Airshow on Sunday. The deal is worth $23 billion at list prices and brings total orders from Emirates alone for the world's largest jetliner to 140 aircraft, its chairman Sheikh Ahmed bin Saeed Al Maktoum told a news conference. (Reporting by Tim Hepher, Praveen Menon)