''Subtiliolithus'' is an oogenus of

fossil egg Egg fossils are the fossilized remains of eggs laid by ancient animals. As evidence of the physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may preserve the remains of t ...

from the Nemegt Formation of

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

and the Ohyamashimo Formation of

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. The eggs are notable for a very thin eggshell. It contains three oospecies: ''S. hyogoensis'', ''S. kachchhensis'' and ''S. microtuberculatus''. They were originally classified as a distinct oofamily, Subtiliolithidae, but numerous similarities to ''Laevisoolithus'' have led to their reclassification as Laevisoolithid eggs. A complete skeleton of '' Nanantius valifanovi'' was found associated with ''Subtiliolithus'' eggshells, indicating that the oogenus represents eggs of

enantiornithine The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...

birds.Kurochkin, E.N., S. Chatterjee, and K.E. Mikhailov. (2013) "An Embryonic Enantiornithine Bird and Associated Eggs from the Cretaceous of Mongolia." ''Paleontological Journal'' 47(11):1252-1269.

References

Egg fossils Fossils of Mongolia Maastrichtian life Nemegt Formation Fossil parataxa described in 1991 {{eggshell-stub