Mosasaurs’ ancestors were most likely similar to marine iguanas of the modern Galapagos Islands, land animals that went into the ocean to feed, according to Everhart. They gave rise to mosasaurs roughly 90 million years ago in waters already dominated by sharks, capable of feeding on whatever they wanted, including mosasaurs.
Within a few million years, mosasaurs got larger, and the roughly 22-foot (6.5- to 7- meter) ginsu shark, Cretoxyrhina mantelli, disappeared. There is no smoking gun, Everhart writes on his website, Oceans of Kansas Paleontology, but based on modern sharks’ vulnerability to fishing, it is possible that mosasaurs, which grew as large as 56 feet (17 meters), may have eaten young ginsu sharks, and the population was unable to recover.
Story: LiveScience | Photo: Wikimedia Commons