<img src = "https://media.npr.org/assets/img/2017/11/30/6_sq-89bac100dbe33c297e78eaaec4c9a619a0258a10-s100-c15.jpg" data-original = "https: //media.npr .org / assets / img / 2017/11/30 / 6_sq-89bac100dbe33c297e78eaaec4c9a619a0258a10-s100.jpg "class =" img lazyOnLoad "alt =" Hundreds of eggs from old flying reptiles can be found in China, and he and a colleague used a technique which compared 146 teeth of various species of extinct crocodiles with those of live animals to determine what they were eating.
"Many of the teeth of extinct crocodiles have the same or much greater complexity than living herbivorous lizards, and that tells me that these animals are likely to eat plants, "Melstrom adds.
Three-dimensional images of modern and ancient crocodiles show how carnivores have simpler teeth than herbivores.
Herbivores have more complicated teeth because plant material is often harder to digest than meat, he says. "The more you can decompose plant material prior to chemical digestion, the more nutrients you can absorb from this food."
The team found examples of crocodiles that were probably herbivorous worldwide – in China, Tanzania, Madagascar, North America and Europe.
As Melstrom conducted the research, he looked for patterns that could explain why the ancient crocodiles repeatedly developed into herbivores.
An initial idea was that they became herbivores when there were no mammals nearby – but then they discovered that some lived next to mammals. They also lived in a completely different environment: "Some of them lived on islands and others in continental interiors, others lived in deserts and others in floodplains."
"I said, 'Oh my God, there is not one single feature that herbivorous crocodiles can experience,' he says. "There currently seem to be many different environments that are completely suitable for herbivorous crocodiles."
It's not clear what kind of plants they ate, though Melstrom says that many of them appeared during the Cretaceous, that is, during flowering, began to thrive. An idea of a wild-looking crocodile nibbling on some pretty flowers is plausible, he says.
And it is also noteworthy that, although the herbivore crocodiles seem to have disappeared at the end of the Cretaceous, Melstrom says their modern relatives do not completely avoid plants.
Nobody would call her an omnivore, he says. These are serious meat eaters. "But it's fascinating that an alligator sometimes wants to eat a piece of fruit while it's lying around, and it does," Melstrom adds. "So it's clear that this ability exists to digest plant material that still exists to some degree in its physiology."