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, and Ren Hirayama et al. documented dinosaur and turtle eggshells in the Kuwajima Formation. However, these eggs were never described in detail. In 2006, the dinosaur-rich Kamitaki locality in the Sasayama 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 ramosus.Description
Nipponoolithus ramosus 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. 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: the outer continuous layer, and the inner mammillary layer. The continuous layer is two to four times thicker than the mammillary layer. Nipponoolithus's 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.