Plagioolithusis anoogenusoffossil egg.It is from the Early Cretaceous of Japan. It was probably laid by abird,making it the oldest known fossilbird egg.[1]
| Plagioolithus Temporal range:
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Egg fossil classification
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| Oofamily: | incertae sedis |
| Oogenus: | †Plagioolithus Imai and Azuma,2015 |
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Description
editPlagioolithusis most notable for having a three-layered eggshell. This trait is widespread in modern birds, but is very rare amongMesozoicfossil eggs. No complete eggs have been found, so the size and shape ofPlagioolithuseggs are unknown. Its eggshell is unornamented and very thin, measuring only 0.44 mm thick. The shell consists of a 0.18 mm mammillary layer (the innermost layer of the shell), a 0.18 mm continuous layer, and a 0.08 mm external layer. The pores are narrow, straight, and constant width throughout the shell.[1]
Parentage
editBecause no embryos are known, the parent ofPlagioolithuscannot be identified with certainty. It was formerly believed that triple-layered eggshells were unique toneognathbirds, but some three-layered eggs have been found containingenantiornithinesand non-aviantheropods,indicating that the presence of a third layer isplesiomorphicamong dinosaurs.[1][2]Therefore, this trait alone cannot be used to assignP. fukuiensisto birds. However, the combination of the third layer, the thin shell, and the smooth external surface suggests thatPlagioolithusbelongs to a bird (though to what type of bird remains unknown).[1]
Distribution
editPlagioolithusis only known from a single formation, theKitadani FormationinFukui, Japan.The date of this formation has generated controversy,[3]but multiple lines of evidence support aBarremianage: zirconfission track datingplaces a correlated formation (theBessandani Formation) at 127 million years old.[1]Also, the presence ofNippononaia ryosekianaand the types ofcharophytessuggest a Barremian age.[1]
Paleobiology
editEven though birds are known to be as old as theLate Jurassic,fossil eggs from before theLate Cretaceousare very rare. Indeed,Plagioolithusis the oldest known trace of bird eggs in the fossil record.[1]
At the Kitadani Formation, numerous other dinosaurs are known to have coexisted withPlagioolithus,includingFukuiraptor,Fukuisaurus,Fukuititan,Koshisaurus,and an unidentified type of non-avian theropod.[4]Also present weregoniopholididcrocodiles,eucryptodireturtles, andamiiformfish. Footprints of variousamphibians,dinosaurs, birds, andpterosaursare known from the Kitadani Formation.[1]
References
edit- ^abcdefghImai, Takuya; Azuma, Yoichi (2015). "The oldest known avian eggshells,Plagioolithus fukuiensis,from the Lower Cretaceous (upper Barremian) Kitadani Formation, Fukui, Japan ".Historical Biology.27(8): 1090–1097.Bibcode:2015HBio...27.1090I.doi:10.1080/08912963.2014.934232.S2CID129113738.
- ^Jackson, Frankie D.; Carricchio, David J.; Corsini, Joseph A. (2013). "Avien Eggs from the Eocene Willwood and Chadron Formations of Wyoming and Nebraska".Journal of Vertebrate Paleontology.33(5): 1190–1201.Bibcode:2013JVPal..33.1190J.doi:10.1080/02724634.2013.769445.S2CID86299573.
- ^Matsukawa, Masaki; Ito, Makoto; Nishida, Naohisa; Koarai, Kazuto; Lockley, Martin (2008). "Reply to the Discussion of Sano et al".Cretaceous Research.29(1): 174–181.Bibcode:2008CrRes..29..174M.doi:10.1016/j.cretres.2006.11.007.
- ^Shibata, Masateru; Azuma, Yoichi (2015)."New basal hadrosauroid (Dinosauria: Ornithopoda) from the Lower Cretaceous Kitadani Formation, Fukui, central Japan"(PDF).Zootaxa.3914(4): 421–440.doi:10.11646/zootaxa.3914.4.3.PMID25661952.