Egg fossil

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Fossilized dinosaur eggs displayed at Indroda Dinosaur and Fossil Park Indroda eggs.JPG
Fossilized dinosaur eggs displayed at Indroda Dinosaur and Fossil Park

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.

Contents

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. [1] [2] 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. [3]

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. [3]

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. [4]

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. [5] Several fossilized fish or amphibian eggs have been classified as ichnogenera, including Mazonova , [6] Archaeoovulus , Chimaerotheca , Fayolia , and Vetacapsula . [7]

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. [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]

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). [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]

Parataxonomy

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:

Testudoid

Geckonoid

Crocodiloid

Mosasauroid

Dinosauroid-spherulitic

Oolithes spheroides Oolithes spheroides (Senckenberg).jpg
Oolithes spheroides

Dinosauroid-prismatic

Ornithoid

Incertae sedis /Unclassified

See also

Related Research Articles

<i>Elongatoolithus</i> Fossil dinosaur eggs

Elongatoolithus is an oogenus of dinosaur eggs found in the Late Cretaceous formations of China and Mongolia. Like other elongatoolithids, they were laid by small theropods, and were cared for and incubated by their parents until hatching. They are often found in nests arranged in multiple layers of concentric rings. As its name suggests, Elongatoolithus was a highly elongated form of egg. It is historically significant for being among the first fossil eggs given a parataxonomic name.

<i>Dendroolithus</i> Oogenus of dinosaur egg

Dendroolithus is an oogenus of Dendroolithid dinosaur egg found in the late Cenomanian Chichengshan Formation, in the Gong-An-Zhai and Santonian Majiacun Formations of China and the Maastrichtian Nemegt and Campanian Barun Goyot Formation of Mongolia. They can be up to 162 mm long and 130 mm wide. These eggs may have been laid by a Therizinosaur, Sauropod, or Ornithopod. The oospecies "D." shangtangensis was originally classified as Dendroolithus, however, it has since been moved to its own distinct oogenus, Similifaveoloolithus. This oogenus is related with embryos of the theropod Torvosaurus

Dictyoolithus is an oogenus of dinosaur egg from the Cretaceous of China. It is notable for having over five superimposed layers of eggshell units. Possibly, it was laid by megalosauroid dinosaurs.

Shixingoolithus is an oogenus of dinosaur egg from the Cretaceous of Nanxiong, China.

<i>Macroelongatoolithus</i> Oogenus of dinosaur egg

Macroelongatoolithus is an oogenus of large theropod dinosaur eggs, representing the eggs of giant caenagnathid oviraptorosaurs. They are known from Asia and from North America. Historically, several oospecies have been assigned to Macroelongatoolithus, however they are all now considered to be a single oospecies: M. carlylensis.

<i>Macroolithus</i> Oogenus of dinosaur egg

Macroolithus is an oogenus of dinosaur egg belonging to the oofamily Elongatoolithidae. The type oospecies, M. rugustus, was originally described under the now-defunct oogenus name Oolithes. Three other oospecies are known: M. yaotunensis, M. mutabilis, and M. lashuyuanensis. They are relatively large, elongated eggs with a two-layered eggshell. Their nests consist of large, concentric rings of paired eggs. There is evidence of blue-green pigmentation in its shell, which may have helped camouflage the nests.

Phaceloolithus is an oogenus of dinosaur egg found in the Fenshui'ao Formation of the Dongting Basin of the Hunan Province of China. The eggs have a subspherical shape, measuring up to 168 mm on the long axis, and having a very thin shell.

Continuoolithus is an oogenus of dinosaur egg found in the late Cretaceous of North America. It is most commonly known from the late Campanian of Alberta and Montana, but specimens have also been found dating to the older Santonian and the younger Maastrichtian. It was laid by an unknown type of theropod. These small eggs are similar to the eggs of oviraptorid dinosaurs, but have a distinctive type of ornamentation.

Ageroolithus is an oogenus of dinosaur egg. It may have been laid by a theropod.

Dispersituberoolithus is an oogenus of fossil egg, which may have been laid by a bird or non-avian theropod.

Prismatoolithidae is an oofamily of fossil eggs. They may have been laid by ornithopods or theropods.

Laevisoolithidae is an oofamily of fossil eggs belonging to the Ornithoid-ratite morphotype. Their eggshells are smooth and very thin, typically less than a millimeter thick. Laevisoolithids may be the eggs of Enantiornithid birds. Eggs of the family were found in the Grès à Reptiles Formation of France and the Nemegt Formation of Mongolia.

Stalicoolithidae is an oofamily of fossil eggs.

Coralloidoolithus is an oogenus of dinosaur egg from the Tiantai Basin in Zhejiang Province, containing a single known oospecies C. shizuiwanensis. Formerly, it was classified in the oogenus Paraspheroolithus; however, it was considered sufficiently different to be classified in its own genus. C. shizuiwanensis is similar to Stalicoolithus, leading to their classification in the same family, Stalicoolithidae.

Similifaveoloolithus is an oogenus of fossil dinosaur egg from the Tiantai basin in Zhejiang Province, China. It is the sole known oospecies of the oofamily Similifaveoloolithidae.

Hemifaveoloolithus is an oogenus of fossil dinosaur egg from the Tiantai basin in Zhejiang Province, China. It is a faveoloolithid, having spherical eggs roughly 13 cm in diameter. The shell is distinctive for being composed of four or five superimposed layers of shell units, and the honeycomb-like arrangement of pore canals.

<span class="mw-page-title-main">Elongatoolithidae</span> Oofamily of dinosaur eggs

Elongatoolithidae is an oofamily of fossil eggs, representing the eggs of oviraptorosaurs. They are known for their highly elongated shape. Elongatoolithids have been found in Europe, Asia, and both North and South America.

Mycomorphoolithus is an oogenus of fossil eggs found in Spain and England. They possibly represent eggshells of non-eusuchian crocodylomorphs, and are similar to, but not part of, the Krokolithidae.

Dictyoolithidae is an oofamily of dinosaur eggs which have a distinctive reticulate organization of their eggshell units. They are so far known only from Cretaceous formations in China.

<i>Gobioolithus</i> Fossil bird egg native to Mongolia

Gobioolithus is an oogenus of fossil bird egg native to Mongolia. They are small, smooth-shelled, and elongated eggs that were first discovered in the 1960s and early 70s during a series of fossil-hunting expeditions in the Gobi Desert. Two oospecies have been described: Gobioolithus minor and G. major. The eggs were probably laid in colonial nesting sites on the banks of rivers and lakes.

References

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