The 1.2 metre-long shark carcass was discovered on the floor of a subway car last night in downtown Manhattan.
"I thought it was just a plush toy or a prank. When I saw the teeth that's I knew it was real, it was no toy," one of the passengers, Juan Cano was quoted by CNN as saying.
The dead shark, described as weighing between two to five kgs, was discovered under a seat with blood on its mouth, thought to be recently caught by a fishing hook.
After several stops, a conductor asked passengers to leave the car and closed it off. The train continued to the end of the line, and then a supervisor placed the shark in a garbage bag and put it in the trash.
This is not the first case of a mysterious shark appearance. Last week, a 5-foot-long shark carcass was discovered outside the door of a bar in Nantucket, Massachusetts.