Titanoboa
Titanoboa cerrejonensis is the largest known snake.  Now extinct, the snake was a relative of the anaconda and the boa constrictor.  It was about 43 feet long (13 m), and weighed over a ton (about 1135 kg or 2,500 pounds).  The snake lived in the Palaeocene epoch, about 58 million years ago.  It ate crocodiles.