why did not find dinosaur eggs in Zigong

 Known as the hometown of Zigong Dinosaur found a large number of dinosaur fossils, but did not find a dinosaur egg fossil. Why is this? There are probably several reasons:
First, the structure of dinosaur eggs have an evolving improvement process, the early egg may not be easy to save and the formation of fossils. Amniotic eggs from reptiles began to appear, it is bound over time, continuous improvement in the evolution of its structure and function, and enhance the adaptability to the environment. This time, eggshell thickness and mineral composition of the increase may be the important aspect. Produced in Zigong Dinosaur fossils for the Jurassic age of the strata, in the early and mid-dinosaur evolution, when the shell is probably not easy to form a dinosaur fossil.

Second, the formation of egg fossils form fossils than the more demanding conditions, Zigong areas natural and geographical environment at that time may not be suitable for the formation of fossils and dinosaur eggs to save.
Third, the Jurassic dinosaur evolution is an important period of development, birth to dinosaur eggs can hatch successfully, and the broken eggshell after hatching is not easy to form a fossil.
Fourth, the Zigong Dinosaur reproduction may not be spawning areas. Some people think that dinosaurs and now has a similar migratory habits of birds, lay their eggs in one place each year, while in other areas of life, very far apart in between. If so, then the Zigong dinosaur may be a suitable place to live, rather than breeding spawning areas.
What kind of reason, we still need to find more and more in-depth study.