Bite marks on fossil bones suggest giant crocodylians were major predators in Miocene South America. The marks point especially to Purussaurus neivensis, a seven-meter relative of modern caimans. The finding helps show that large reptiles, not only mammal predators, shaped ancient food webs around a vast lake system. A broken fossil bone can hold the last trace of an attack. In Miocene South America, some of those marks point to giant crocodylians ruling the edges of an ancient lake. More than 10 million years ago, a vast lake covered much of the continent. Its waters and shores supported giant turtles, crocodylians, anacondas, saber-toothed mammals, flightless “terror birds” and sebecids, terrestrial relatives of crocodylians. The prey were enormous too. Giant ground sloths, glyptodonts and several kinds of ungulates lived along the lake’s shores. Some of those hoofed mammals, including astrapotheres and toxodontids, could weigh well over a tonne. A recent study argues that crocodylians were the most significant predator group in this habitat. The conclusion comes from bite and tooth marks preserved on herbivore fossils between …