Jiranrai of Left Alxa Banner, Inner Mongolia possesses an open and undulating terrain. From the northern border of the salt pond to the mountain appears the stratum of the Mesozoic Era in the geological history, especially the sediment formed during the Early Cretaceous Period and the Late Cretaceous Period, which is widely distributed and very thick and is regarded as a "graveyard" where ancient reptiles including dinosaurs are forever sleeping. In the past decades, paleontologists at home and abroad have conducted several investigations here and discovered a lot of dinosaur fossils of the Cretaceous Period, including the well-know Maortuensis and Tashuikouensis. But what makes the paleontologists gasp with admiration is that a total of four sets of complete fossil skeleton of Probactrosaurus have been found, which is a miracle in the history of Probactrosaurus excavation.
What should be noticed is that in Jirantai three broods of dinosaur fossil eggs were unearthed, from which twenty-seven intact fossil eggs and many shell fragments were found. The shape of these fossil eggs is quite unique; they are round fossil eggs, which are not easily seen at home. What's more, they are big, with the biggest diameter as 140 millimeters, comparable with a relatively small ostrich egg. With air holes structured like a honeycomb, dinosaur eggs of this kind is a new type in paleontology, named as "Jirantai Honeycomb Egg", which is distinguished among the dinosaur egg fossils at home and abroad.
According to experts, in the same area of Jirantai lie the "forerunners" of dinosaur family living in the Early Cretaceous Period130 million years ago as well as the "descendants" of the thriving dinosaur family in the Late Cretaceous Period 70 million years ago. The stratum and fossils here are not only like a set of systematic and well-preserved archives but also like a perfect natural museum, which recreate the scene of billions of years ago when dinosaurs were originating, evolving, thriving and declining.