How can dinosaur sexes be distinguished?

In general it is difficult to tell male and female dinosaurs apart. Most of the parts of the body which indicate the sex of an animal are soft and fleshy and therefore do not preserve as fossils. The sex organs of reptiles are usually located under flap-like scales or inside their bodies which makes it difficult to distinguish the sexes. In rare cases it may be possible to tell the sex of a dinosaur by anatomical markers. For example Professor Peter Dodson found that the crests on the heads of duck-billed dinosaurs in N.America, could either be large or small although of the same shape. He suggested that since these dinosaurs lived together at the same time and in the same place that they were actually male and female of the same species. This has been accepted by most dinosaur palaeontologists.