Egg fossil

Egg fossilsare thefossilizedremains ofeggslaid byancientanimals. As evidence of thephysiologicalprocesses of an animal, egg fossils are considered a type oftrace fossil. Under rare circumstances a fossil egg may preserve the remains of the once-developingembryoinside, 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 includeinvertebrateslikeammonoidsas well asvertebrateslikefishes, possibleamphibians, andreptiles. The latter group includes the manydinosaur eggsthat 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.In 1859, the first scientifically documented dinosaur egg fossils were discovered in southern France by a Catholicpriestand amateur naturalist named FatherJean-Jacques Poech, however he thought they were laid by giant birds.
The first scientificallyrecognizeddinosaur egg fossils were discoveredserendipitouslyin 1923 by anAmerican Museum of Natural Historycrew while looking for evidence ofearly humansin Mongolia. Egg discoveries continued to mount all over the world, leading to the development of multiple competing classification schemes. In 1975 Chinese paleontologistZhao Zi-Kuistarted a revolution in fossil egg classification by developing a system of "parataxonomy" based on the traditionalLinnaeansystem 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 Mikhailovbrought attention to Zhao's work in the English languagescientific literature.
Eggs laid by invertebrate animals are known from the fossil record. Among these are eggs laid by ancientcephalopods. Eggs laid byammonoidsare the best known cephalopod egg fossils. The best preserved fossil ammonite eggs were preserved in theJurassicKimmeridge ClayofEngland. Nevertheless, thefossil recordof 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.
Fossil fish eggs have an extensiverecordgoing at least as far back as theDevonianand spanning into theCenozoic era. The eggs of many different fishtaxahave 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.Several fossilized fish or amphibian eggs have been classified as ichnogenera, includingMazonova,Archaeoovulus,Chimaerotheca,Fayolia, andVetacapsula.
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.Some ancient reptiles, like ichthyosaursand plesiosaursare known to have given live birth and are therefore not anticipated to have left behind egg fossils.Dinosaur eggsare 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:
Testudoid
Geckonoid
Crocodiloid
Mosasauroid
Dinosauroid-spherulitic
Dinosauroid-prismatic
Ornithoid
Incertae sedis/Unclassified