Some dinosaurs were utterly bizarre. You may have heard of them before, but one particular group called therizinosaurs belonged to the meat-eating theropod dinosaurs (those that led to birds), were really awesome. However, they actually at some point made a conscious evolutionary decision to stop being badasses, and become Cretaceous-cauliflower* munching pansies.
What comes to mind when you think of dinosaur interaction? Large carnivores chomping on unsuspecting little ornithopods? Ceratopsians jousting for their next mate? Large hadrosaurs tenderly mothering their cute newborns? There are many possible images of community-level dinosaur interactions, and there is a host of evidence out there that take dinosaurs beyond the bones and breathe new life into how they lived.
How do you tell between different dinosaurs, when you don’t have any dinosaurs? Trace fossils, like footprints, are ghosts of dinosaurs past, remnants of life entombed within the rocks. Palaeontologists and ichnologists (scientists who study trace fossils, not fish) often used to get confused by the question of matching a dinosaur track to its maker. Dinosaur tracks are known from multiple localities all around the globe, but figuring out exactly which dinosaurs made them, or even what type of dinosaur, has always been a mystery. How do you tell the difference? A classic example of this uncertainty is between the tracks of ornithopod and theropod dinosaurs – both groups walked on two feet (bipedal, mostly – some ornithopods were variably quadrupedal), had the same size ranges, were clawed, and had three front toes (mostly). This means that often, the trackways looked quite similar, not just in terms of gross morphology, but also in the stride length, which tells us about how fast an animal was moving at the time.
Sometimes, the trackmaker can be a little easier to identify.. Source