Why is there so much argument about the origin of birds?

The difficulty in explaining the evolution of birds is that there are so few fossils. Bird bones are very fragile and honeycombed, with small air spaces. They crumbled away very easily after death, and consequently bird are extremely rare.

The only fossils of ancient birds are those where the animals fell into shallow freshwater lagoons and were covered very quickly with mud, which prevented decay or scattering of the remains by predators or scavengers. These special conditions appeared only occasionally, however. Until more types of bird fossil are found it will be difficult for scientists to fill in the evolutionary gaps and fin out more about the origin of birds.