Nipponoolithus

''Nipponoolithus'' is an oogenus of fossil egg native to Japan. It is one of the smallest known dinosaur eggs, and was probably laid by some kind of non-avian maniraptor.

Distribution

''Nipponoolithus'' remains are known from the Sasayama Group in Kamitaki, southeastern Tamba, Hyogo, Japan. The site is dated to the lower Albian.

History

Though fossil dinosaur skeletons are rare in Japan, they have been well-documented since 1978. The first Japanese fossil eggs were discovered in 2003: Yoichi Azuma documented numerous eggs of the Ratite morphotype in the Kitadani Formation,Azuma, Y. (2003).
Early Cretaceous vertebrate remains from Katsuyama city, Fukui Prefecture, Japan.
''Memoir of the Fukui Prefectural Dinosaur Museum,'' 2: 17–21 and Ren Hirayama ''et al.'' documented dinosaur and turtle eggshells in the Kuwijima Formation.Hirayama, R., Manabe, M., Isaji, S., Barrett, P.M., Evans, S.E., Yabumoto, Y.,
Matsuoka, H., Yamaguchi, I., Yamaguchi, M., (2003)
Vertebrate fauna from the Early Cretaceous Kuwajima Formation of Shiramine Village, Ishikawa Prefecture, central Japan.
''Memoir of the Fukui Prefectural Dinosaur Museum,'' 2: 15–16 However, these eggs were never described in detail. In 2006, the dinosaur-rich Kamitaki locality in the Sasayam Group was discovered. In 2016, a team of paleontologists from Japan and Canada collected numerous fossilized eggs at Kamitaki, including the specimens which they would refer to a new oogenus and oospecies: ''Nipponoolithus rumosus''.

Description

''Nipponoolithus rumosus'' is known only from a handful of isolated eggshell fragments ranging from 0.36 to 0.53 mm in thickness, just barely larger than a chicken egg.Tanaka, K., Zelenitsky, D. K., Saegusa, H., Ikeda, T., DeBuhr, C. L., & Therrien, F. (2016). Dinosaur eggshell assemblage from Japan reveals unknown diversity of small theropods. Cretaceous Research, 57, 350–363.Miller, KK (2015).
World’s smallest dinosaur egg just discovered in Hyogo Prefecture
''Rocket News 24''. It is estimated, based on the eggshell thickness, that ''Nipponoolithus'' eggs weighed about , making it among the smallest fossil dinosaur eggs ever discovered.

Like most non-avian dinosaur eggs, it has two layers:Laura E. Wilson, Karen Chin, Frankie D. Jackson, and Emily S. Bray
II. Eggshell morphology and structure
''UCMP Online Exhibits: Fossil Eggshell'' the outer continuous layer, and the inner mammillary layer. The continuous layer is two to four times thicker than the mammillary layer. ''Nipponoolithuss outer surface is ornamented with low, branched ridges, similar to ornamentation observed in ''Macroelongatoolithus'', ''Montanoolithus'', '' Paraelongatoolithus'', '' Reticuloolithus'', '' Spheruprismatoolithus'', and the eggs of '' Deinonychus''. The crystals in the mammillary layer are acicular or wedge-like.

Paleobiology

''N. rumosus'' was most likely laid by some kind of non-avian maniraptor because of its similarities in microstructure and ornamentation to oviraptorosaur eggs and the eggs of ''Deinonychus''. Other very small theropod eggs (ranging in size from to ), including '' Elongatoolithus'', '' Prismatoolithus'' (and other indeterminate prismatoolithids), as well as ornithopod eggs assigned to '' Spheroolithus'', are also known from the Kamitaki site. These eggs, along with skeletal remains, show that the parents of ''Nipponoolithus'' coexisted with numerous other small theropods, as well as an assemblage of ankylosaurs, titanosaurs, hadrosauroids, tyrannosaurs, and therizinosaurs. The parent of ''Nipponoolithus'' probably weighed roughly , comparable to the size of some contemporary small theropods from the Jehol biota in China.

Parataxonomy

''Nipponoolithus'' has not been place into any described oofamily. It contains a single oospecies: ''N. rumosus''.

References

{{Taxonbar, from=Q24907647

Dinosaur reproduction
Egg fossils
Fossil parataxa described in 2016
Extinct animals of Japan
Prehistoric maniraptorans
Fossils of Japan