Egg fossils oroofossils are thefossilized remains ofeggs laid byancientanimals. As evidence of thephysiological processes of an animal, egg fossils are considered a type oftrace fossil. Under rare circumstances a fossil egg may preserve the remains of the once-developingembryo inside, in which case it also containsbody fossils. A wide variety of different animal groups laid eggs that are now preserved in the fossil record beginning in thePaleozoic. Examples includeinvertebrates likeammonoids as well asvertebrates likefishes, possibleamphibians, andreptiles. The latter group includes the manydinosaur eggs that have been recovered fromMesozoicstrata. 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 theLinnaean system. This "parataxonomy" is calledveterovata.
The first named oospecies wasOolithes bathonicae, a name given provisionally by Professor J. Buckman to a group of eggs which Buckman believed were laid by ateleosaur. However, modern scientists no longer think it is possible to determine what kind of reptile laid these eggs.[1][2] In 1859, the first scientifically documented dinosaur egg fossils were discovered in southern France by a Catholicpriest and amateur naturalist named FatherJean-Jacques Poech, however he thought they were laid by giant birds.[3]
The first scientificallyrecognized dinosaur egg fossils were discoveredserendipitously in 1923 by anAmerican Museum of Natural History crew while looking for evidence ofearly humans in Mongolia. Egg discoveries continued to mount all over the world, leading to the development of multiple competing classification schemes. In 1975 Chinese paleontologistZhao Zi-Kui started a revolution in fossil egg classification by developing a system of "parataxonomy" based on the traditionalLinnaean 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 paleontologistKonstantin Mikhailov brought attention to Zhao's work in the English languagescientific literature.[3]
Eggs laid by invertebrate animals are known from the fossil record. Among these are eggs laid by ancientcephalopods. Eggs laid byammonoids are the best known cephalopod egg fossils. The best preserved fossil ammonite eggs were preserved in theJurassicKimmeridge Clay ofEngland. Nevertheless, thefossil 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, thebelemnoids, 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.[4]
Fossil fish eggs have an extensiverecord going at least as far back as theDevonian and spanning into theCenozoic era. The eggs of many different fishtaxa have contributed to this record, includinglobe-finned fish,placoderms, andsharks. Occasionally eggs are preserved still within the mother's body, or associated with fossilembryos. Some fossil eggs possibly laid by fish cannot be confidently distinguished from those laid byamphibians.[5] Several fossilized fish or amphibian eggs have been classified as ichnogenera, includingMazonova,[6]Archaeoovulus,Chimaerotheca,Fayolia, andVetacapsula.[7]
The fossil record of reptile eggs goes back at least as far as theEarly Permian. However, since the earliest reptile eggs probably had soft shells with littlepreservation potential, reptilian eggs may go back significantly farther than their fossil record. Many ancient reptile groups are known from egg fossils includingcrocodilians,dinosaurs, and turtles.[3] Some ancient reptiles, like ichthyosaurs[8] and plesiosaurs[9] 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.[3]
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).[2][10] 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.[3]
The oogenus level parataxonomy of Veterovata, following Lawver and Jackson (2014)[11] for Testudoid, Hirsch (1996)[12] for Geckonoid eggs, and Mikhailov et al. (1996)[2] for the rest unless otherwise noted:
^Buckman, J. (1860). "On some fossil reptilian eggs from the Great Oolite of Cirencester".Quarterly Journal of the Geological Society of London.16 (1–2):107–110.doi:10.1144/gsl.jgs.1860.016.01-02.11.S2CID129871634.
^abcdefgCarpenter, Kenneth (1999).Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past), Indiana University Press;ISBN0-253-33497-7.
^Cloutier, R (2010). "The fossil record of fish ontogenies: insights to developmental patterns and processes".Semin Cell Dev Biology.21 (4):400–413.doi:10.1016/j.semcdb.2009.11.004.PMID19914384.
^Capasso, L.L.; Pallizzi, A.; Milia, L.; D'Anastasio, R. (2013). "Archaeoovulus palenae, n. gn., n. sp. (Icnofossilia): a fossil amphibious ootheca from the pre-evaporitic Messinian site of Capo di Fiume, Palena (Abruzzo)".Atti della Societa Toscana di Scienze Naturali Residente in Pisa Memorie Serie A.120:25–38.
^Ellis, Richard, (2003)Sea Dragons - Predators of the Prehistoric Oceans. University Press of Kansas.ISBN0-7006-1269-6.
^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.
^abJackson, F. D.; Jin, X.; Varricchio, D. J.; Azuma, Y.; Jiang, Y. (2008). "The first in situ turtle clutch from the Cretaceous Tiantai Basin, Zhejiang Province, China".Journal of Vertebrate Paleontology.28 (2):319–325.doi:10.1671/0272-4634(2008)28[319:tfistc]2.0.co;2.S2CID130212532.
^abcdeQiang, Wang; Zi-kui, Zhao; Xiao-lin, Wang; Yan-gen, Jiang (2011). "New ootypes of dinosaur eggs from the Late Cretaceous in Tiantai Basin, Zhejiang Province, China".Vertebrata PalAsiatica.49 (4):446–449.
^abAgnolin, Federico L.; Powell, Jaime E.; Novas, Fernando E.; Kundrát, Martin (2012). "New alvarezsaurid (Dinosauria, Theropoda) from uppermost Cretaceous of north-western Patagonia with associated eggs".Cretaceous Research.35:33–56.Bibcode:2012CrRes..35...33A.doi:10.1016/j.cretres.2011.11.014.ISSN0195-6671.
^abcE. 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
^D. 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
^abcdZelenitsky, D. K.; Hills, L. V.; Currie, P. J. (1996). "Parataxonomic classification of ornithoid eggshell fragments from the Oldman Formation (Judith River Group; Upper Cretaceous), southern Alberta".Canadian Journal of Earth Sciences.33 (12):1655–1667.Bibcode:1996CaJES..33.1655Z.doi:10.1139/e96-126.
^Jin, X.; Azuma, Y.; Jackson, F. D.; Varricchio, D. J. (2007). "Giant dinosaur eggs from the Tiantai basin, Zhejiang province, China".Canadian Journal of Earth Sciences.44 (1):81–88.Bibcode:2007CaJES..44...81J.doi:10.1139/e06-077.
^Garcia, 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,
^abVarricchio, D.J.; Barta, D.E. (2015). "Revisiting Sabath's 'Larger Avian Eggs' from the Gobi Cretaceous".Acta Palaeontologica Polonica.60 (1):11–25.
^Moreno-Azanza, Miguel; Ignacio Canudo, Jose; Manuel Gasca, Jose (2015). "Enigmatic Early Cretaceous ootaxa from Western Europe with signals of extrinsic eggshell degradation".Cretaceous Research.56:617–627.Bibcode:2015CrRes..56..617M.doi:10.1016/j.cretres.2015.06.019.
^Tanaka, 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.Bibcode:2016CrRes..57..350T.doi:10.1016/j.cretres.2015.06.002.
^Mikhailov, 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).
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