Nipponoolithusis anoogenusoffossil eggnative toJapan.It is one of the smallest known dinosaur eggs, and was probably laid by some kind of non-avianmaniraptor.[1]
| Nipponoolithus Temporal range:
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|---|---|
Egg fossil classification
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| Oofamily: | incertae sedis |
| Oogenus: | †Nipponoolithus Tanaka et al. 2016 |
| Oospecies | |
Distribution
editNipponoolithusremains are known from theSasayama Groupin Kamitaki, southeasternTamba, Hyogo,Japan. The site is dated to the lowerAlbian.[1]
History
editThough fossil dinosaur skeletons are rare in Japan, they have been well-documented since1978.[1]The first Japanese fossil eggs were discovered in2003:Yoichi Azuma documented numerous eggs of theRatite morphotypein theKitadani Formation,[2]and Ren Hirayamaet al.documented dinosaur and turtle eggshells in theKuwijima Formation.[3]However, these eggs were never described in detail.[1]In2006,the dinosaur-rich Kamitaki locality in the Sasayam Group was discovered. In2016,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]
Description
editNipponoolithus rumosusis 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, thatNipponoolithuseggs weighed about 100 grams (3.5 oz), making it among the smallest fossil dinosaur eggs ever discovered.[1]
Like most non-aviandinosaur 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 inMacroelongatoolithus,Montanoolithus,Paraelongatoolithus,Reticuloolithus,Spheruprismatoolithus,and the eggs ofDeinonychus.[1]The crystals in the mammillary layer areacicularor wedge-like.[1]
Paleobiology
editN. rumosuswas most likely laid by some kind of non-avianmaniraptorbecause of its similarities in microstructure and ornamentation tooviraptorosaureggs and the eggs ofDeinonychus.Other very small theropod eggs (ranging in size from 27 grams (0.95 oz) to 135 grams (4.8 oz)), includingElongatoolithus,Prismatoolithus(and other indeterminateprismatoolithids), as well as ornithopod eggs assigned toSpheroolithus,are also known from the Kamitaki site. These eggs, along with skeletal remains, show that the parents ofNipponoolithuscoexisted with numerous other small theropods, as well as an assemblage ofankylosaurs,titanosaurs,hadrosauroids,tyrannosaurs,andtherizinosaurs.The parent ofNipponoolithusprobably weighed roughly 15 kilograms (33 lb), comparable to the size of some contemporary small theropods from theJehol biotain China.[1]
Parataxonomy
editNipponoolithushas not been place into any described oofamily. It contains a single oospecies:N. rumosus.[1]
References
edit- ^abcdefghijklTanaka, 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.
- ^Azuma, Y. (2003). "Early Cretaceous vertebrate remains from Katsuyama city, Fukui Prefecture, Japan."Memoir of the Fukui Prefectural Dinosaur Museum,2: 17–21
- ^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
- ^Miller, KK (2015). "World’s smallest dinosaur egg just discovered in Hyogo Prefecture"Rocket News 24.
- ^Laura E. Wilson, Karen Chin, Frankie D. Jackson, and Emily S. Bray.II. Eggshell morphology and structure.UCMP Online Exhibits: Fossil Eggshell