"The skeleton of a young aquatic reptile, known as Sinohydrosaurus lingyuanensis, is the first fossil ever unearthed which has two heads and necks, showing that a developmental abnormality seen in modern snakes, turtles, lizards and crocodiles also afflicted their ancient forebears."
Talk about a rare find!
A pic of the fossil, by investigator Eric Buffetaut, can be viewed here.
Special thanks to nutmeg.