A trove of 84-million-year-old fossils recently discovered in western Hungary belongs to what appears to be a family of a new mosasaur species. Mosasaurs are large crocodile-like reptiles from between 66 to 100 million years ago that, until now, scientists believed only lived in marine environments. The fossils belong to a species that paleontologists have named Pannoniasaurus inexpectatus, the first mosasaur species discovered to live in freshwater. The research team, led by Laszlo Makadi, a paleontologist at the Hungarian Natural History Museum, was excited to find not just one organism’s fossil, but a number of Pannoniasaurus specimens representing a range of ages. Finding juvenile specimens’ fossils is unusual in itself, but finding them alongside adults is even rarer, and tells scientists a whole lot about how that species lived. Makadi and colleagues believe that, due to the variety of ages of specimens, these Mosasaurs lived in groups with more than one family unit, and lived their whole lives in freshwater, versus arriving there later in life from a marine environment.