Sexual Dimorphsim Dinosaur

It is very difficult to determine which fossils were male and which were female. Some paleontologists have theorized that the males of some species may have had larger crests, frills, or other showy structures that were used in courtship displays, mating rituals, and/or intraspecies rivalry (contests among members of the same species, like territorial disputes and mating competition), very much like many modern-day animals. The development of these structures occurs with sexual maturity, so example of juvenile fossils would have little or none of these structures.

Hadrosaurs Originally, fossils very similar to Parasaurolophus but with smaller crests were thought to belong to a separate species of Parasaurolophus. A similar situation existed for Lambeosaurus and many other crested dinosaurs (the lambeosaurine duck-bills) and dome-headed dinosaurs (Pachycephalosaurs). In 1975, the Canadian paleontologist Peter Dodson showed that many of the supposedly separate species of frilled/crested dinosaurs were the females and juveniles of the species. The anatomist James A. Hopson also interpreted the crest and dome sizes as differing in males and females within a species.

Ceratopsians - Many paleontologists believe that the ceratopsians (like Triceratops and Protoceratops) used their horns and frills in territorial disputes, in mating competitions and for attracting females.

Pachycephalosaurs, the dome-headed hadrosaurid dinosaurs, also exhibit sexual dimorphism. The anatomist James A. Hopson realized that crest and dome size differs in the male and female of the species.