Palaeontologists have found a fossil that has all of the skeletal features which reveal it to be the great great grandparent of the sauropod dinosaurs like diplodocus, brachiosaurus and apatosaurus. The sauropods are well known for having been gentle giants. While they were absolutely enormous, their teeth make it clear that they never ate anything other than plants. We always figured that their ancestors were likely to have only eaten plants too and we were clearly wrong.
You do not have to be a palaeontologist to look at these teeth and know they were definitely not for chewing on leaves! It is a very cool finding that raises tonnes of questions like "what animals was this sauropod hunting" and "what forces drove its descendants to ultimately go vegetarian". You can read more in The Economist article that I wrote on this here.