|University of Bristol|
Living teiid lizards are known to prey on crocodile (caiman) eggs. It is possible that they also preyed on dinosaur eggs although there is no direct evidence (Kirkland, 1994). Living varanid lizards will eat any egg. They often prey on reptile nests and mound-building birds (Cott 1961). Large varanids, such as the African Monitor, show little fear of adult crocodiles. They are active carnivores and will eat hatched young if found, some even eating parents. It is possible that varanid lizards could have preyed on dinosaur eggs; specimens have been found close to Troodon eggs in Montana (Horner 1987).
Pterosaurs and Birds
Most dinosaurs at least partially buried their eggs, which would prevent pterosaurs simply flying by and stealing the eggs. Just how mobile and agile pterosaurs are on the ground is still in great debate but to infiltrate a nest and steal the eggs would entail a considerable deal of agility. Birds often steal eggs today, during breeding season, so maybe they also preyed on dinosaur eggs in the Cretaceous.
The theropod dinosaurs Oviraptor and Troodon have been accused in the past of preying on the eggs. Evidence now indicates they could actually be caring for the eggs. So although evidence for dinosaur egg predation by dinosaurs is dubious, it still probably happened.