See text Elongatoolithus is an oogenus of dinosaur eggs found in the Late Cretaceous formations of China and Mongolia.

The eggs are highly elongated, typically being 2 to 2.2 times longer than they are wide, and slightly asymmetric (with one end pointier than the other).

[1] Within these two groups, oospecies vary primarily by eggshell thickness, ratio of continuous to mammillary layer, and overall size of the eggs.

While most eggs are preserved without any trace of embryo or parent, several elongatoolithid nests have been found in association with skeletons of adult oviraptorosaurs.

[2] An adult Citipati skeleton was discovered in the Upper Cretaceous of Mongolia associated with a nest of eggs most likely referable to E.

[2] The type specimen of E. andrewsi consists of a well preserved nest, containing eleven eggs arranged in at least two circular layers.

[7][16] In 1954, Chinese paleontologist Yang Zhongjian described several fossil eggs from Laiyang, including an elongated type which he named "Oolithes" elongatus.

[6] In 1975, the Chinese paleontologist Zhao Zikui published the prototype of the modern parataxonomic system for eggshell classification, dividing fossil eggs into oospecies, oogenera, and oofamilies.

[5] In 1979 another oospecies, E. magnus, was discovered and named by the Chinese paleontologists Zeng Demin and Zhang Jinjian, based on a nest of nine eggs uncovered in Hunan.

[10] In 1991, the Russian paleontologist Konstantin Mikhailov created the modern, formal classification scheme for fossil eggs.

[17] In 1994, when Mikhailov described and reviewed the fossil elongated eggs from Mongolia, he named four new oospecies of Elongatoolithus (E. excellens, E. frustrabilis, E. subtitectorius, and E. sigillarius) as well as mentioning two other unnamed forms.

[11] In 2000, the Chinese paleontologists Fang Xiaosi, Wang Yaozhong, and Jiang Yan'gen described several ootaxa from the egg-rich Tiantai Basin, including the oospecies E.

They argued that E. chichengshanensis should belong to a new group, E. laijiaensis required further study to determine its affinities, and E. tiantaiensis should be moved to Prismatoolithidae.