Dinosaur progeny were born from eggs. These eggs were of varying size and shape: for example, some were round and others were long and narrow. Also, an examination of the way fossils were produced reveals that their eggs were laid in various ways. Some dug holes in which to lay their eggs, others built circular earthen mounds and laid their eggs inside, and so on. There have been many cases where the species of an egg was unknown, but eggs with preserved embryos have now been discovered, making it possible to determine parentage.