Egg fossils 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.
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 Poech, 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.
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.
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 ichthyosaurs 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.
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). 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.
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:
- Spheruflexibilis morphotype
- Spherurigidis morphotype
- Oofamily Cairanoolithidae
- Oofamily Stalicoolithidae
- Oofamily Spheroolithidae
- Oofamily Phaceloolithidae
- Oofamily Ovaloolithidae
- Oofamily Megaloolithidae
- Oofamily Similifaveoloolithidae
- Oofamily Faveoloolithidae
- Oofamily Youngoolithidae
- Oofamily Dendroolithidae
- Oofamily Dictyoolithidae
- Oofamily Polyclonoolithidae
- Oofamily Arriagadoolithidae
- Oofamily Prismatoolithidae
- Ornithoid-ratite Morphotype
- Oofamily Elongatoolithidae
- Oofamily Laevisoolithidae
- Oofamily Medioolithidae
- Oofamily Montanoolithidae
- Oofamily Oblongoolithidae
- Ornithoid-prismatic Morphotype
- Oofamily Pachycorioolithidae
- 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.
- Konstantin E. Mikhailov, Emily S. Bray & Karl E. Hirsch (1996). "Parataxonomy of fossil egg remains (Veterovata): basic principles and applications". Journal of Vertebrate Paleontology. 16 (4): 763–769. doi:10.1080/02724634.1996.10011364. JSTOR 4523773.
- Carpenter, Kenneth (1999). Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past), Indiana University Press; ISBN 0-253-33497-7.
- Etches, S.; Clarke, J.; Callomon, J. (2009). "Ammonite eggs and ammonitellae from the Kimmeridge Clay Formation (Upper Jurassic) of Dorset, England". Lethaia. 42 (2): 204–217. doi:10.1111/j.1502-3931.2008.00133.x.
- 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. PMID 19914384.
- Godfrey, S.J. (1995). "Fossilized Eggs from the Pennsylvanian of Illinois". Ichnos: An International Journal for Plant and Animal Traces. 4 (1): 71–75. doi:10.1080/10420949509380115.
- 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. ISBN 0-7006-1269-6.
- O'Keefe, F.R.; Chiappe, L.M. (2011). "Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia)". Science. 333 (6044): 870–873. Bibcode:2011Sci...333..870O. doi:10.1126/science.1205689. PMID 21836013.
- 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.
- Lawver, D.R.; Jackson, F.D. (2014). "A Review of the Fossil Record of Turtle Reproduction: Eggs, Embryos, Nests and Copulating Pairs". Bulletin of the Peabody Museum of Natural History. 55 (2): 215–236. doi:10.3374/014.055.0210.
- Hirsch, K.F. (1996). "Parataxonomic Classification of Fossil Chelonian and Gecko Eggs". Journal of Vertebrate Paleontology. 16 (4): 752–762. doi:10.1080/02724634.1996.10011363.
- Jackson, 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.
- Wang, Q.; Wang, X.; Zhao, Z.; Zhang, J.; Jiang, S. (2013). "New turtle egg fossil from the Upper Cretaceous of the Laiyang Basin, Shandong Province, China" (PDF). Anais da Academia Brasileira de Ciências. 85 (1): 103–111. doi:10.1590/s0001-37652013000100008. PMID 23538955.
- Oliveira, C.E.M.; Santucci, R.M.; Andrade, M.B.; Fulfaro, V.J.; Basílo, J.A.F.; Benton, M.J. (2011). "Crocodylomorph eggs and eggshells from the Adamantina Formation (Bauru Group), Upper Cretaceous of Brazil". Palaeontology. 54 (2): 309–321. doi:10.1111/j.1475-4983.2010.01028.x. S2CID 131247549.
- Legendre, Lucas J.; David Rubilar Rogers; Grace M. Musser; Sarah N. Davis; Rodrigo A. Otero; Alexander O. Vargas, and Julia A. Clarke. 2020. A giant soft-shelled egg from the Late Cretaceous of Antarctica. Nature .. .. Accessed 2020-06-17.
- Sellés, A. G., & Galobart, À. (2015). Reassessing the endemic European Upper Cretaceous dinosaur egg Cairanoolithus. Historical Biology, (ahead-of-print), 1-14.
- Wang, Q; Wang, X L; Zhao, Z K; Jiang, Y G (2012). "A new oofamily of dinosaur egg from the Upper Cretaceous of Tiantai Basin, Zhejiang Province, and its mechanism of eggshell formation". Chinese Science Bulletin. 57 (28–29): 3740–3747. Bibcode:2012ChSBu..57.3740W. doi:10.1007/s11434-012-5353-2.
- Moreno-Azanza, M.; Canudo, J.I.; Gasca, J.M. (2014). "Spheroolithid eggshells in the Lower Cretaceous of Europe. Implications for eggshell evolution in ornithischian dinosaurs" (PDF). Cretaceous Research. 51: 75–87. doi:10.1016/j.cretres.2014.05.017.
- Vianey-Liaud, M.; López-Martínez, N. (1997). "Late Cretaceous dinosaur eggshells from the Tremp basin, southern Pyrenees, Lleida, Spain". Journal of Paleontology. 71 (6): 1157–1171. doi:10.1017/s002233600003609x.
- Qiang, 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.
- Zhang, S. K. (2010). "A parataxonomic revision of the Cretaceous faveoloolithid eggs of China" (PDF). Vertebrata PalAsiatica. 48 (3): 203–219. Retrieved 3 October 2015.
- Xie, 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. Archived 2016-01-29 at the Wayback Machine" Vertebrata PalAsiatica, 54(1):1-10.
- Agnolin, 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. doi:10.1016/j.cretres.2011.11.014. ISSN 0195-6671.
- Jackson, F. D.; Varricchio, D. J. (2010). "Fossil eggs and eggshell from the lowermost Two Medicine Formation of western Montana, Sevenmile Hill locality". Journal of Vertebrate Paleontology. 30 (4): 1142–1156. doi:10.1080/02724634.2010.483537.
- López-Martínez, N.; Vicens, E. (2012). "A new peculiar dinosaur egg, Sankofa pyrenaica oogen. nov. oosp. nov. from the Upper Cretaceous coastal deposits of the Aren Formation, South-Central Pyrenees, Lleida, Catalonia, Spin". Palaeontology. 55 (2): 325–339. doi:10.1111/j.1475-4983.2011.01114.x.
- E. 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
- Moreno-Azanza, M.; Canudo, J.I.; Gasca, J.M. (2014). "Unusual theropod eggshells from the Early Cretaceous Blesa Formation of the Iberian Range, Spain" (PDF). Acta Palaeontologica Polonica. 59 (4): 843–854.
- 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
- Zelenitsky, 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.
- Wang, Q.; Wang, X.-L.; Zhao, Z.-K.; Jiang, Y.-G. (2010). "A new oogenus of Elongatoolithidae from the Upper Cretaceous Chichengshan Formation of Tiantai Basin, Zhejiang Province" (PDF). Vertebrata PalAsiatica. 48 (2): 111–118.
- 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.
- Wang, Q.; Zhao, Z.; Wang, X.; Li, N.; Zou, S. (2013). "A new form of Elongatoolithidae, Undulatoolithus pengi oogen. et oosp. nov. from Pingxiang, Jiangxi, China" (PDF). Zootaxa. 3746 (1): 194–200. doi:10.11646/zootaxa.3746.1.9. PMID 25113475.
- 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,
- Jackson, Frankie D.; Varricchio, David J.; Corsini, Joseph A. (2013). "Avian Eggs from the Eocene Willwood and Chadron Formations of Wyoming and Nebraska". Journal of Vertebrate Paleontology. 33 (5): 1190–1201. doi:10.1080/02724634.2013.769445.
- Zelenitsky, D. K.; Therrien, F. (2008). "Unique maniraptoran egg clutch from the Upper Cretaceous Two Medicine Formation of Montana reveals theropod nesting behaviour". Palaeontology. 51 (6): 1253–1259. doi:10.1111/j.1475-4983.2008.00815.x.
- Varricchio, 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 Westerm Europe with signals of extrinsic eggshell degradation". Cretaceous Research. 56: 617–627. 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. doi:10.1016/j.cretres.2015.06.002.
- Zhang, S.; Jin, X.; O'Conner, J.K.; Wang, M.; Xie, J. (2015). "A new egg with avian egg shape from the Upper Cretaceous of Zhejiang Province, China". Historical Biology. 27 (5): 595–602. doi:10.1080/08912963.2014.902451.
- 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).
- Imai, 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. doi:10.1080/08912963.2014.934232.
- Lawver, Daniel R.; Jin, Xingsheng; Jackson, Frankie D.; Wang, Qiongying (2016). "An Avian Egg from the Lower Cretaceous (Albian) Liangtoutang Formation of Zhejiang Province, China". Journal of Vertebrate Paleontology. 36 (3): e1100631. doi:10.1080/02724634.2016.1100631.