Egg fossil

Egg fossils or oofossils are the fossilized remains of eggs laid by ancient animals. As evidence of the physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may preserve the remains of the once-developing embryo inside, in which case it also contains body fossils. A wide variety of different animal groups laid eggs that are now preserved in the fossil record beginning in the Paleozoic. Examples include invertebrates like ammonoids as well as vertebrates like fishes, possible amphibians, and reptiles. The latter group includes the many dinosaur eggs that have been recovered from Mesozoic strata. Since the organism responsible for laying any given egg fossil is frequently unknown, scientists classify eggs using a parallel system of taxonomy separate from but modeled after the Linnaean system. This "parataxonomy" is called veterovata.

History

The first named oospecies was Oolithes bathonicae, a name given provisionally by Professor J. Buckman to a group of eggs which Buckman believed were laid by a teleosaur. However, modern scientists no longer think it is possible to determine what kind of reptile laid these eggs. In 1859, the first scientifically documented dinosaur egg fossils were discovered in southern France by a Catholic priest and amateur naturalist named Father Jean-Jacques Pouech; however, he thought they were laid by giant birds.

The first scientifically recognized dinosaur egg fossils were discovered serendipitously in 1923 by an American Museum of Natural History crew while looking for evidence of early humans in Mongolia. Egg discoveries continued to mount all over the world, leading to the development of multiple competing classification schemes. In 1975 Chinese paleontologist Zhao Zi-Kui started a revolution in fossil egg classification by developing a system of "parataxonomy" based on the traditional Linnaean system to classify eggs based on their physical qualities rather than their hypothesized mothers. Zhao's new method of egg classification was hindered from adoption by Western scientists due to language barriers. However, in the early 1990s Russian paleontologist Konstantin Mikhailov brought attention to Zhao's work in the English language scientific literature.

Diversity

Invertebrates

Eggs laid by invertebrate animals are known from the fossil record. Among these are eggs laid by ancient cephalopods. Eggs laid by ammonoids are the best known cephalopod egg fossils. The best preserved fossil ammonite eggs were preserved in the Jurassic Kimmeridge Clay of England. Nevertheless, the fossil record of cephalopod eggs is scant since their soft, gelatinous eggs decompose quickly and have little chance to fossilize. Another major group of Mesozoic cephalopods, the belemnoids, have no documented eggs in the fossil record whatsoever, although this may be because scientists have not properly searched for them rather than an actual absence from the fossil record.

Fishes and amphibians

Fossil fish eggs have an extensive record going at least as far back as the Devonian and spanning into the Cenozoic era. The eggs of many different fish taxa have contributed to this record, including lobe-finned fish, placoderms, and sharks. Occasionally eggs are preserved still within the mother's body, or associated with fossil embryos. Some fossil eggs possibly laid by fish cannot be confidently distinguished from those laid by amphibians. Several fossilized fish or amphibian eggs have been classified as ichnogenera, including Mazonova, Archaeoovulus, Chimaerotheca, Fayolia, and Vetacapsula.

Reptiles

The fossil record of reptile eggs goes back at least as far as the Early Permian. However, since the earliest reptile eggs probably had soft shells with little preservation potential, reptilian eggs may go back significantly farther than their fossil record. Many ancient reptile groups are known from egg fossils including crocodilians, dinosaurs, and turtles. Some ancient reptiles, like ichthyosaursEllis, Richard, (2003) Sea Dragons - Predators of the Prehistoric Oceans. University Press of Kansas. . and plesiosaurs are known to have given live birth and are therefore not anticipated to have left behind egg fossils. Dinosaur eggs are among the most well known kind of fossil reptile eggs.

Classification Fossil eggs are classified according to the parataxonomic system called Veterovata. There are three broad categories in the scheme, on the pattern of organismal phylogenetic classification, called oofamilies, oogenera and oospecies (collectively known as ootaxa).Olga Amo, Gloria Cuenca–Bescós & José Ignacio Canudo (1999). José Ignacio Canudo & Gloria Cuenca-Bescós, ed. "Vertebrate eggshell fragments from the Lower Cretaceous (Lower Barremian) of Camino Canales (Galve Bassin, Province of Teruel, NE Spain)" (PDF). IV European Workshop on Vertebrate Palaeontology. Albarracín, Spain: Universidad de Zaragoza. The names of oogenera and oofamilies conventionally contain the root "oolithus" meaning "stone egg", but this rule is not always followed. They are divided up into several basic types: Testudoid, Geckoid, Crocodiloid, Dinosauroid-spherulitic, Dinosauroid-prismatic, and Ornithoid. Veterovata does not always mirror the taxonomy of the animals which laid the eggs.Carpenter, Kenneth (1999). Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past), Indiana University Press; .

Parataxonomy The oogenus level parataxonomy of Veterovata, following Lawver and Jackson (2014) for Testudoid, Hirsch (1996) for Geckonoid eggs, and Mikhailov et al. (1996) for the rest unless otherwise noted:

Testudoid Spheruflexibilis morphotype Oofamily Testudoflexoolithidae Testudoflexoolithus Spherurigidis morphotype Oofamily Testudoolithidae Testudoolithus Emydoolithus Haininchelys ChelonoolithusGeckoid Geckonoid morphotype Oofamily Gekkoolithidae Gekkoolithus GekkonidovumCrocodiloid Oogenus Mycomorphoolithus Oofamily Krokolithidae Bauruoolithus Krokolithes SuchoolithusDinosauroid-spherulitic Placoolithus Sphaerovum Stromatoolithus Tacuarembovum Oofamily Cairanoolithidae CairanoolithusSellés, A. G., & Galobart, À. (2015). Reassessing the endemic European Upper Cretaceous dinosaur egg Cairanoolithus. Historical Biology, (ahead-of-print), 1-14. Oofamily Stalicoolithidae Coralloidoolithus Shixingoolithus Stalicoolithus

Oofamily Spheroolithidae Guegoolithus Spheroolithus Paraspheroolithus Oofamily Phaceloolithidae Phaceloolithus Oofamily Ovaloolithidae Ovaloolithus Oofamily Megaloolithidae Megaloolithus Pseudomegaloolithus Oofamily Similifaveoloolithidae Similifaveoloolithus Oofamily Umbellaoolithidae Umbellaoolithus Oofamily Faveoloolithidae Faveoloolithus Hemifaveoloolithus Parafaveoloolithus Oofamily Youngoolithidae Youngoolithus Oofamily Dendroolithidae Dendroolithus Oofamily Dictyoolithidae Dictyoolithus Paradictyoolithus Protodictyoolithus Oofamily Polyclonoolithidae PolyclonoolithusXie, J.-F., Zhang, S.-K., Jin, X.-S., Li, D.-Q., and Zhou, L.-Q. (2016) "A new type of dinosaur eggs from Early Cretaceous of Gansu Province, China. " Vertebrata PalAsiatica, 54(1):1-10.Dinosauroid-prismatic Pseudogeckoolithus Oofamily Arriagadoolithidae Arriagadoolithus Triprismatoolithus Oofamily Prismatoolithidae Preprismatoolithus Prismatoolithus Protoceratopsidovum Sankofa SpheruprismatoolithusE. S. Bray. 1999. Eggs and eggshell from the Upper Cretaceous North Horn Formation, central Utah. In D. D. Gillette (ed.), Vertebrate Paleontology in Utah, Utah Geological Survey Miscellaneous Publication 99-1:361-375 TrigonoolithusOrnithoid Ornithoid-ratite Morphotype Ageroolithus Diamantornis Ornitholithus ReticuloolithusD. K. Zelenitsky and W. J. Sloboda. 2005. Eggshells. In P. J. Currie and E. B. Koppelhus (eds.), Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Indiana University Press, Bloomington 398-404 Struthiolithus Tristraguloolithus Tubercuoolithus Oofamily Elongatoolithidae Continuoolithus Ellipsoolithus Elongatoolithus Heishanoolithus Macroelongatoolithus Macroolithus Nanhsiungoolithus Paraelongatoolithus Porituberoolithus Rodolphoolithus Spongioolithus Trachoolithus Undulatoolithus Oofamily Laevisoolithidae Laevisoolithus Subtiliolithus TipoolithusGarcia, G., T. Rodolphe, H. Cappetta, B. Marandat, I. Bentaleb, A. Benabdallah and M. Vianey-Liaud. (2003). "First Record of Dinosaur Eggshels and Teeth from The North-West African Maastrichtian (Morocco)." Palaeovertebrata, Montpellier, 32 (2-4): 59-69, Oofamily Medioolithidae Incognitoolithus Microolithus Medioolithus Oofamily Montanoolithidae Montanoolithus Oofamily Oblongoolithidae Oblongoolithus Ornithoid-prismatic Morphotype Dispersituberoolithus Oofamily Gobioolithidae GobioolithusIncertae sedis/Unclassified Oolithes Metoolithus Mosaicoolithus Mycomorphoolithus Nipponoolithus Parvoblongoolithus ParvoolithusMikhailov, K.E. (1997). Fossil and recent eggshell in amniotic vertebrates: Fine structure, comparative morphology and classification. Special Papers in Palaeontology 56. The Palaeontological Association. London. (page 58). Plagioolithus Styloolithus Oofamily Pachycorioolithidae Pachycorioolithus Soft-shelled eggs Squamatorum Lacertidovum, material consisted non-diagnostic and possibly not an egg at all by Mikhailov (1997). Mosasaur? Antarcticoolithus

Egg fossil

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