Scientists have found fossils that actually show different behaviors, such as live birth, predation, herding, and even parental care. In addition, scientists can examine the behavior of animals today and combine that knowledge with the physical evidence from fossils to develop hypotheses about how the extinct creatures lived. They can test their predictions with additional lines of evidence. So, scientists can examine muscle attachment sites in the legs of T. rex, the organization of the melanosomes of fossil feathers, or the structure of nasal passages of hadrosaurs, and compare those data to data from living animals. As a result, they can gain insight to how dinosaurs ran, how they may have used feathers in courtship display (a behavior common in modern birds), and how they communicated.