
Egg fossils are the
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
ized remains of
eggs laid by
ancient animal
Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...
s. 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
vertebrate
Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain.
The vertebrates make up the subphylum Vertebra ...
s like
fishes
A fish (: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed ...
, possible
amphibian
Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...
s, and
reptile
Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...
s. The latter group includes the many
dinosaur eggs that have been recovered from
Mesozoic
The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
strata
In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...
. 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 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.
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
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
Kimmeridge Clay of
England
England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
. 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
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
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
Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...
.
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,
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
s, and turtles.
Some ancient reptiles, like ichthyosaurs
[Ellis, 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''
*** '' Chelonoolithus''
Geckoid
* Geckonoid morphotype
** Oofamily Gekkoolithidae
*** '' Gekkoolithus''
*** '' Gekkonidovum''
Crocodiloid
* Oogenus Mycomorphoolithus
''Mycomorphoolithus'' (meaning "fungus-shaped stone egg") is an oogenus of fossil eggs found in Spain and England. They possibly represent eggshells of non-eusuchian Crocodylomorpha, crocodylomorphs, and are similar to, but not part of, the Krokol ...
* Oofamily Krokolithidae
** '' Bauruoolithus''
** '' Krokolithes''
** '' Suchoolithus''
Mosasauroid
* '' Antarcticoolithus''
Dinosauroid-spherulitic
* '' Placoolithus''
* '' Sphaerovum''
* '' Stromatoolithus''
* '' Tacuarembovum''
* Oofamily Cairanoolithidae
** '' Cairanoolithus''[Sellés, 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 Faveoloolithidae
** '' Faveoloolithus''
** '' Hemifaveoloolithus''
** '' Parafaveoloolithus''
* Oofamily Youngoolithidae
** '' Youngoolithus''
* Oofamily Dendroolithidae
** '' Dendroolithus''
* Oofamily Dictyoolithidae
** '' Dictyoolithus''
** '' Paradictyoolithus''
** '' Protodictyoolithus''
* Oofamily Polyclonoolithidae
** '' Polyclonoolithus''[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.
" ''Vertebrata PalAsiatica'', 54(1):1-10.
Dinosauroid-prismatic
* '' Pseudogeckoolithus''
* Oofamily Arriagadoolithidae
** '' Arriagadoolithus''
** '' Triprismatoolithus''
* Oofamily Prismatoolithidae
** '' Preprismatoolithus''
** '' Prismatoolithus''
** '' Protoceratopsidovum''
** '' Sankofa''
** '' Spheruprismatoolithus''[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]
** '' Trigonoolithus''
Ornithoid
* Ornithoid-ratite Morphotype
** '' Ageroolithus''
** '' Diamantornis''
** '' Ornitholithus''
** '' Reticuloolithus''[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]
** '' Struthiolithus''
** '' Tristraguloolithus''[
** '' Tubercuoolithus''][
** Oofamily Elongatoolithidae
*** '' Continuoolithus'']
*** '' Ellipsoolithus''
*** '' Elongatoolithus''
*** '' Heishanoolithus''[
*** '' Macroelongatoolithus'']
*** '' Macroolithus''
*** '' Nanhsiungoolithus''
*** '' Paraelongatoolithus''[
*** '' Porituberoolithus''][
*** '' Rodolphoolithus'']
*** '' Spongioolithus''[
*** '' Trachoolithus''
*** '' Undulatoolithus'']
** Oofamily Laevisoolithidae
*** '' Laevisoolithus''
*** '' Subtiliolithus''
*** '' Tipoolithus''[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,]
** Oofamily Medioolithidae
*** '' Incognitoolithus''[
*** '' Microolithus'']
*** '' Mediolithus''
** Oofamily Montanoolithidae
*** '' Montanoolithus''[
** Oofamily Oblongoolithidae]
*** '' Oblongoolithus''
* Ornithoid-prismatic Morphotype
** '' Dispersituberoolithus''[
** Oofamily Gobioolithidae]
*** '' Gobioolithus''
'' Incertae sedis/Unclassified''
* '' Oolithes''
* '' Metoolithus''
* '' Mosaicoolithus''
* ''Mycomorphoolithus
''Mycomorphoolithus'' (meaning "fungus-shaped stone egg") is an oogenus of fossil eggs found in Spain and England. They possibly represent eggshells of non-eusuchian Crocodylomorpha, crocodylomorphs, and are similar to, but not part of, the Krokol ...
''
* '' Nipponoolithus''
* '' Parvoblongoolithus''
* '' Parvoolithus''[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).]
* '' Plagioolithus''
* '' Styloolithus''[
* Oofamily Pachycorioolithidae
** '' Pachycorioolithus'']
See also
* Fossil footprint
* Coprolite
References
External links
UCMP's online fossil egg exhibit
Paleofile
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