were at a late stage in development when they died. Their wings and shoulders are especially well-developed. Only the modern megapodes and the little tern exhibit a comparable degree of embryonic ossification in the arm and shoulder bones. It is likely that Gobipipus hatchlings, like megapodes and little terns, would be able to fly very soon after hatching. No embryos are known from G. major eggs, but they are usually assumed to have been laid by a similar type of bird. NestsGobioolithus eggs were probably laid in open nests on the banks of ephemeral rivers or lakes, which could frequently flood the nesting areas and bury the eggs. The distribution of the eggs suggests that they had a long-term colonial nesting site at the Khermeen Tsav locality in the Barun Goyot Formation. At the Bayn-Dzak locality, the eggs are typically arranged in clutches, whereas elsewhere they are scattered randomly, each oriented nearly vertically in the substrate. The solitary eggs may have been laid and buried individually, similar to the nesting habits of modern megapodes. It is also possible that they were originally laid in clutches, but flooding separated them and deposited them vertically as the water level dropped. Water damage would also explain why Gobioolithus shells are frequently heavily recrystallized. Classification According to the parataxonomic system used to classify fossil eggs, Gobioolithus is classified in the oofamily Gobioolithidae, which, in turn, is classified in the prismatic morphotype (also called the neognath morphotype) of the ornithoid basic type. A cladistic analysis performed by Varricchio and Barta (2015) (pictured below) found Gobioolithus to be a sister taxon to Styloolithus. However, they considered Styloolithus different enough from Gobioolithus to warrant its exclusion from Gobioolithidae. DistributionGobioolithus is found in the Gobi desert in Mongolia. More specifically, the fossils are found in the Barun Goyot and the Djadokhta Formations of the Nemegt Basin, which is dated to the Upper Cretaceous. History Numerous fossils, including Gobioolithus specimens, were discovered and collected by the Polish-Mongolian fossil-hunting expeditions in the Gobi desert from 1963 to 1971 and by the Soviet-Mongolian expeditions between 1969 and 1996. These fossils were brought to the Institute of Paleobiology of the Polish Academy of Sciences in Warsaw and to the Paleontological Institute of the Russian Academy of Sciences in Moscow. Eggs now classified as Gobioolithus were first analyzed in 1981 by the Polish paleontologist Andrzej Elżanowski, who described several well-developed bird embryos within