Tylosaurus pembinensis (Marsh, 1872)
Central / Western United States
Length: 15 m
More than a century after Cope and Marsh first dug up fossils of this giant squamate, our view of her has changed drastically. We now know that she possessed an asymmetrical tail fluke, was countershaded, lacked a dorsal crest, and is most likely more closely related to monitor lizards than she is to snakes.