| Nipponoolithus Temporal range: | |
|---|---|
Egg fossil classification  | |
| Oofamily: | incertae sedis |
| Oogenus: | † Nipponoolithus Tanaka et al. 2016 |
| Oospecies | |
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. [1]
Nipponoolithus remains are known from the Sasayama Group in Kamitaki, southeastern Tamba, Hyogo, Japan. The site is dated to the lower Albian. [1]
Though fossil dinosaur skeletons are rare in Japan, they have been well-documented since 1978. [1] The first Japanese fossil eggs were discovered in 2003: Yoichi Azuma documented numerous eggs of the Ratite morphotype in the Kitadani Formation, [2] and Ren Hirayama et al. documented dinosaur and turtle eggshells in the Kuwijima Formation. [3] However, these eggs were never described in detail. [1] 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. [1]
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. [1] [4] It is estimated, based on the eggshell thickness, that Nipponoolithus eggs weighed about 100 grams (3.5 oz), making it among the smallest fossil dinosaur eggs ever discovered. [1]
Like most non-avian dinosaur eggs, it has two layers: [5] the outer continuous layer, and the inner mammillary layer. [1] 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 . [1] The crystals in the mammillary layer are acicular or wedge-like. [1]
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 27 grams (0.95 oz) to 135 grams (4.8 oz)), 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 15 kilograms (33 lb), comparable to the size of some contemporary small theropods from the Jehol biota in China. [1]
Nipponoolithus has not been place into any described oofamily. It contains a single oospecies: N. rumosus. [1]
Elongatoolithus is an oogenus of dinosaur eggs found in the Late Cretaceous formations of China and Mongolia. Like other elongatoolithids, they were laid by small theropods, and were cared for and incubated by their parents until hatching. They are often found in nests arranged in multiple layers of concentric rings. As its name suggests, Elongatoolithus was a highly elongated form of egg. It is historically significant for being among the first fossil eggs given a parataxonomic name.
Dictyoolithus is an oogenus of dinosaur egg from the Cretaceous of China. It is notable for having over five superimposed layers of eggshell units. Possibly, it was laid by megalosauroid dinosaurs.
Macroelongatoolithus is an oogenus of large theropod dinosaur eggs, representing the eggs of giant caenagnathid oviraptorosaurs. They are known from Asia and from North America. Historically, several oospecies have been assigned to Macroelongatoolithus, however they are all now considered to be a single oospecies: M. carlylensis.
Macroolithus is an oogenus of dinosaur egg belonging to the oofamily Elongatoolithidae. The type oospecies, M. rugustus, was originally described under the now-defunct oogenus name Oolithes. Three other oospecies are known: M. yaotunensis, M. mutabilis, and M. lashuyuanensis. They are relatively large, elongated eggs with a two-layered eggshell. Their nests consist of large, concentric rings of paired eggs. There is evidence of blue-green pigmentation in its shell, which may have helped camouflage the nests.
Continuoolithus is an oogenus of dinosaur egg found in the late Cretaceous of North America. It is most commonly known from the late Campanian of Alberta and Montana, but specimens have also been found dating to the older Santonian and the younger Maastrichtian. It was laid by an unknown type of theropod. These small eggs are similar to the eggs of oviraptorid dinosaurs, but have a distinctive type of ornamentation.
Dispersituberoolithus is an oogenus of fossil egg, which may have been laid by a bird or non-avian theropod.
Sankofa is an oogenus of prismatoolithid egg. They are fairly small, smooth-shelled, and asymmetrical. Sankofa may represent the fossilized eggs of a transitional species between non-avian theropods and birds.
Montanoolithus is an oogenus of fossil egg found in Montana and Alberta. They were probably laid by a dromaeosaur or a caenagnathid.
Styloolithus is an oogenus of highly distinctive fossil egg from the Upper Cretaceous Djadokhta Formation and the Barun Goyot Formation in Mongolia.
Elongatoolithidae is an oofamily of fossil eggs, representing the eggs of oviraptorosaurs. They are known for their highly elongated shape. Elongatoolithids have been found in Europe, Asia, and both North and South America.
Guegoolithus is an oogenus of fossil egg from the early Cretaceous of Spain. It is classified in the oofamily Spheroolithidae, and was probably laid by an ornithopod dinosaur.
Undulatoolithus is an oogenus of Chinese fossil dinosaur egg belonging to Elongatoolithidae. It is very similar to Macroolithus, but has different ornamentation. Like other elongatoolithids, it was probably laid by oviraptorosaurs.
Dictyoolithidae is an oofamily of dinosaur eggs which have a distinctive reticulate organization of their eggshell units. They are so far known only from Cretaceous formations in China.
Triprismatoolithus is an oogenus of dinosaur egg native to Teton County, Montana. It is classified in the oofamily Arriagadoolithidae, the eggs of alvarezsaurs.
Trigonoolithus is an oogenus of dinosaur egg, representing a basal prismatoolithid. Its eggshell, like avian eggs, is composed of three structural layers, but cladistic analysis suggests that its parent was a non-avian theropod.
Incognitoolithus is an oogenus of medioolithid fossil bird egg. It is notable for bearing evidence of predation, possibly from a bird pecking the eggshell.
Gobioolithus is an oogenus of fossil bird egg native to Mongolia. They are small, smooth-shelled, and elongated eggs that were first discovered in the 1960s and early 70s during a series of fossil-hunting expeditions in the Gobi desert. Two oospecies have been described: Gobioolithus minor and G. major. The eggs were probably laid in colonial nesting sites on the banks of rivers and lakes.
Pachycorioolithus is an oogenus of small, thin-shelled fossil egg from the early Cretaceous in China. It probably belongs to a bird, though there is a possibility the parent was a non-avian theropod. It was named in 2016, based on a single specimen found in Zhejiang.
Plagioolithus is an oogenus of fossil egg. It is from the Early Cretaceous of Japan. It was probably laid by a bird, making it the oldest known fossil bird egg.
Nanhsiungoolithus is an oogenus of dinosaur egg from the late Cretaceous of China. It belongs to the oofamily Elongatoolithidae, which means that it was probably laid by an oviraptorosaur, though so far no skeletal remains have been discovered in association with Nanhsiungoolithus. The oogenus contains only a single described oospecies, N. chuetienensis. It is fairly rare, only being know from two partially preserved nests and a few eggshell fragments.