This timeline of egg fossils research is a chronologically ordered list of important discoveries, controversies of interpretation, taxonomic revisions, and cultural portrayals of egg fossils. Humans have encountered egg fossils for thousands of years. In Stone Age Mongolia, local peoples fashioned fossil dinosaur eggshell into jewelry. In the Americas, fossil eggs may have inspired Navajo creation myths about the human theft of a primordial water monster's egg. Nevertheless, the scientific study of fossil eggs began much later. As reptiles, dinosaurs were presumed to have laid eggs from the 1820s on, when their first scientifically documented remains were being described in England. In 1859, the first scientifically documented dinosaur egg fossils were discovered in southern France by a Catholic priest and amateur naturalist named Father Jean-Jacques Pouech, however he thought they were laid by giant birds. The first scientifically recognized dinosaur egg fossils were discovered serendipitously in 1923 by an American Museum of Natural History crew while looking for evidence of early humans in Mongolia. These eggs were mistakenly attributed to the locally abundant herbivore Protoceratops, but are now known to be Oviraptor eggs. Egg discoveries continued to mount all over the world, leading to the development of multiple competing classification schemes. In 1975 Chinese paleontologist Zhao Zi-Kui started a revolution in fossil egg classification by developing a system of "parataxonomy" based on the traditional Linnaean system to classify eggs based on their physical qualities rather than their hypothesized mothers. Zhao's new method of egg classification was hindered from adoption by Western scientists due to language barriers. However, in the early 1990s Russian paleontologist Konstantin Mikhailov brought attention to Zhao's work in the English language scientific literature.
Prescientific
Late Paleolithic to early Neolithic Mongolians fashioned fossil dinosaur eggshell into jewelry. Mongolia’s Flaming Cliffs are known as "one of the greatest dinosaur fossil sites the world has ever seen".
Precolumbian North America A common theme in Navajo stories about Water Monsters involve the human theft of Water Monster eggs or young and the angry Monsters pursuing humanity through a series of worlds. Stories like this influenced the Navajos to fear large fossil bones, which they felt shouldn't be disturbed, because doing so might awaken the enraged ghosts of the Water Monsters, who might resume their rampage with apocalyptic results. Stories like this may have been based on the discovery of fossil eggs in western North America. Fossil eggs and nests from this region that may have inspired the legend were left behind by creatures like possible aetosaurs, giant condors, duck-billed dinosaurs, possible phytosaurs, large theropods, and sea turtles.
19th-century paleontology
1859 The first scientifically documented dinosaur egg fossils were discovered in southern France by a Catholic priest and amateur naturalist named Father Jean-Jacques Pouech. These fossils were large chunks of eggshell that date back to the Late Cretaceous. Pouech mistook them for the shell of a giant bird's eggs.
1869 French geologist Philippe Matheron made a fossil discovery in the same general region as Pouech. Matheron discovered the fossil bones of an animal he named Hypselosaurus. Matheron thought Hypselosaurus to be a crocodile-like animal, but it is now recognized as a long-necked herbivorous sauropod dinosaur. Eggshell fossils were found associated with the remains. Matheron presented the shell fossils to the director of comparative anatomy at Paris' Natural History Museum, Paul Gervais. Gervais examined thin sections of the shell fossils and compared them with similar thin sections of eggs laid by modern birds and reptiles. He found them to be most similar to turtle eggs, but recognized that since dinosaur eggs had not yet been described scientifically, he could not rule out that possibility.
20th-century paleontology
1913 While prospecting on the Blackfoot Reservation of northern Montana on behalf of the National Museum of Natural History, Charles W. Gilmore found a deposit of apparent freshwater clam fossils. He collected samples, noted the location and photographed the site. These "clamshell" fossils were actually the first dinosaur eggshell collected by scientists in the United States.
1919 Roy Chapman Andrews proposed the idea of a scientific expedition into central Asia to test Henry Fairfield Osborn's hypothesis that humanity originated in Asia.
1922 17 April: The Central Asiatic Expedition, led by Andrews, departed from Peking toward Mongolia.
1923 13 July: Over dinner, Central Asiatic Expedition member George Olsen claimed to have found fossil eggs. The other expedition members were skeptical, but Olsen took them to the site of his find. Expedition paleontologist W. Granger recognized them as dinosaur eggs, but mistakenly believed them to be the first ever discovered.
1939 Alfred Sherwood Romer and Lewellyn Price described a 5.9 cm by 3.79 cm fossil egg from the Lower Permian as the oldest hard-shelled fossil egg. The composition of its shell would later be disputed, but if the fossil was correctly identified as a reptile egg it is the oldest known.
1946 Summer: Soviet scientists embarked on an expedition to Mongolia retracing part of the journey taken by the Central Asiatic Expedition. They discovered many additional dinosaur eggs, some from previously undiscovered fossil sites.
1957 The first scientifically documented dinosaur eggs from India were discovered by M. Sahni.
1964 The first scientifically documented dinosaur eggshell from Canada was discovered on the banks of the Milk River in southern Alberta.
1966 Paleontologist U. Lehman made the first plausible report of ammonite egg fossils in the scientific literature. The apparent clutch of eggs was preserved in the sediment that filled in the living chamber of a harboceratid dating back to the Toarcian age of the Jurassic period. The fossil itself was discovered in a concretion incorporated into glacial drift that came from the Baltic region. The shell containing the putative eggs was a fully grown individual with a macroconch shell.
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