Dinosaur eggs are represented today as fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s. They represent the product of egg

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 laying activity and can offer clues as to how dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s behaved. In some cases the embryonic dinosaur is preserved within the eggshell, and can be studied.

Dinosaur eggs are known from about 200 sites around the world, the majority in Asia and mostly in terrestrial

Terrestrial animal

Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

 (nonmarine) rocks of Cretaceous Age. It may be that thick calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

 eggshells evolved during the Cretaceous (145 to 66 million years ago). Most dinosaur eggs have one of two forms of eggshell that are distinct from the shells of related modern animal groups, such as turtle

Turtle

Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...

s or bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s. However, some dinosaur eggs closely resemble bird eggs, particularly the type of eggshells in ostrich

Ostrich

The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...

 eggs.

The oldest known dinosaur eggs are from Massospondylus

Massospondylus

Massospondylus and ) is a genus of prosauropod dinosaur from the early Jurassic Period . It was described by Sir Richard Owen in 1854 from remains found in South Africa, and is thus one of the first dinosaurs to have been named...

, which lived during the Early Jurassic

Early Jurassic

The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...

, about 190 million years ago.

History

The first real discovery of dinosaur eggshell was in 1859 from southern France, by Jean Jacques Pouech. Due to their large size, the French eggs were at first thought to belong to giant birds. More complete eggs were found in 1869 by Matheron. He, in turn, believed these eggs were those of a giant crocodile

Crocodile

A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

.

In 1877, Paul Gervais

Paul Gervais

For the Canadian parliamentarian see Paul Mullins GervaisPaul Gervais full name François Louis Paul Gervaise was a French palaeontologist and entomologist.-Biography:...

 published the first detailed study of the eggs, and suggested that they could belong to a dinosaur. They are now known to have been laid by the sauropod

Sauropoda

Sauropoda , or the sauropods , are an infraorder of saurischian dinosaurs. They had long necks, long tails, small heads , and thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land...

 dinosaur Hypselosaurus

Hypselosaurus

Hypselosaurus was a long titanosaurid sauropod that lived in Europe during the Late Cretaceous Period .Hypselosaurus was scientifically described by geologist Pierre Émile Philippe Matheron in 1846 and formally named in...

.

Size

Dinosaur eggs vary in size, depending on the species. Among the largest are fossilized dinosaur eggs collected in the mid 1990s from Late Cretaceous rocks in China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

. These eggs are more than 60 cm (2 ft.) long and about 20 cm (8 in.) in diameter.

Types

The egg structure consists of a series of basic vertical units that grow from particular sites on the surface of the shell. The organisation of these units determines the classification scheme, being either spherulitic

Spherulite

In petrology, spherulites are small, rounded bodies that commonly occur in vitreous igneous rocks. They are often visible in specimens of obsidian, pitchstone and rhyolite as globules about the size of millet seed or rice grain, with a duller luster than the surrounding glassy base of the rock,...

 or prismatic:

• Spherulitic egg shells show spherical patterns in the crystalline structure, and they are seen in sauropods and hadrosaurs
  Hadrosaurid
  Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...
  
  .
• Prismatic
  Prism (geometry)
  In geometry, a prism is a polyhedron with an n-sided polygonal base, a translated copy , and n other faces joining corresponding sides of the two bases. All cross-sections parallel to the base faces are the same. Prisms are named for their base, so a prism with a pentagonal base is called a...
  
   egg shells grow into spherical crystals only in the lower portion of the shell, while crystals in the upper portion are prisms.
• Ornithoid eggs (also seen in birds) are generally laid by theropods
  Theropoda
  Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
  
  . In this type only the very bottom part of the shell exists as separate or discrete units (mammilae). The upper and mid-portions of the shell consist of a mass of biocrystalline material with a spongy (squamatic) ultrastructure, that comprises a homogeneous layer.

The shape of dinosaur eggs may reflect some aspects of their biology. In general, they are more symmetrical than bird eggs, implying that the head was not given more priority than other structures during development. Like birds, the shell was likely an important source of calcium, especially later in development. In modern reptiles, calcium from the shell is mobilized and stored in the yolk sac immediately prior to hatching. A spherical egg would have provided the smallest shell surface compared to the volume of the egg but many dinosaur eggs were elongated. This shape would have increased the total volume of an egg given the diameter of the passage between the pubic bones. It would also have greatly increased the area of calcium-rich shell available to the embryo and may have been important in animals producing precocious young with large well-developed legs and a long bony tail.

Embryos

Dinosaur embryos, the animal inside the eggs, are very rare but useful to understand ontogeny

Ontogeny

Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...

, heterochrony

Heterochrony

In biology, heterochrony is defined as a developmental change in the timing of events, leading to changes in size and shape. There are two main components, namely the onset and offset of a particular process, and the rate at which the process operates...

, and dinosaur systematics

Systematics

Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...

.
The known dinosaurs embryos include:

• Massospondylus
  Massospondylus
  Massospondylus and ) is a genus of prosauropod dinosaur from the early Jurassic Period . It was described by Sir Richard Owen in 1854 from remains found in South Africa, and is thus one of the first dinosaurs to have been named...
  
  
• Lourinhanosaurus
  Lourinhanosaurus
  Lourinhanosaurus was a carnivorous theropod dinosaur genus that lived during the Late Jurassic Period . Its first remains were found at Peralta, near Lourinhã, Portugal in 1982, but were not described until 1998, by Portuguese paleontologist Octávio Mateus.Its type species is L...
  
  (Ricqlès et al., 2001)
• Protoceratops
  Protoceratops
  Protoceratops is a genus of sheep-sized herbivorous ceratopsian dinosaur, from the Upper Cretaceous Period of what is now Mongolia. It was a member of the Protoceratopsidae, a group of early horned dinosaurs...
  
  
• Troodon
  Troodon
  Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...
  
  
• Oviraptorids
• Therizinosauroid

Oogenera

Oogenera are taxonomic names for types of eggshell. Nearly three dozen oogenera have been named for dinosaur eggs:

• Ageroolithus
  Ageroolithus
  Ageroolithus is an oogenus of dinosaur egg. It may belong to a therapod.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Apheloolithus
• Boletuoolithus
• Cairanoolithus
  Cairanoolithus
  Cairanoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Continuoolithus
  Continuoolithus
  Continuoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Dendroolithus
  Dendroolithus
  Dendroolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Dictyoolithus
  Dictyoolithus
  Dictyoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Dispersituberoolithus
  Dispersituberoolithus
  Dispersituberoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Dughioolithus
  Dughioolithus
  Dughioolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Ellipsoolithus
  Ellipsoolithus
  Ellipsoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  

• Elongatoolithus
  Elongatoolithus
  Elongatoolithus is an oogenus of dinosaur egg. In some subjects it is considered a raptor but there is no evidence of it being a maniraptoran....
  
  
• Faveoolithus
  Faveoolithus
  Faveoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Heishanoolithus
• Laevisoolithus
  Laevisoolithus
  Laevisoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Macroolithus
  Macroolithus
  Macroolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Macroelongatoolithus
  Macroelongatoolithus
  Macroelongatoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Megaloolithus
  Megaloolithus
  Megaloolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Nanshiungoolithus
  Nanshiungoolithus
  Nanshiungoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Oblongoolithus
  Oblongoolithus
  Oblongoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Ovaloolithus
  Ovaloolithus
  Ovaloolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  

• Paraspheroolithus
• Phaceloolithus
  Phaceloolithus
  Phaceloolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Placoolithus
• Porituberoolithus
  Porituberoolithus
  Porituberoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Preprismatoolithus
  Preprismatoolithus
  Preprismatoolithus is a Late Jurassic oogenus. The species P. coloradensis is described by John Foster as being "of the prismatic basic type," with subspherical eggs about 10 cm in diameter...
  
  
• Prismatoolithus
  Prismatoolithus
  Prismatoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Protoceratopsidovum
  Protoceratopsidovum
  Protoceratopsidovum is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Pseudogeckoolithus
  Pseudogeckoolithus
  Pseudogeckoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Shixingoolithus
  Shixingoolithus
  Shixingoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Sphaerovum
  Sphaerovum
  Sphaerovum is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  

• Spheroolithus
  Spheroolithus
  Spheroolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Spheruprismatoolithus
• Spongioolithus
• Stromatoolithus
  Stromatoolithus
  Stromatoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Subtiliolithus
  Subtiliolithus
  Subtiliolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Tacumarembovum
• Trachoolithus
  Trachoolithus
  Trachoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Tristraguloolithus
  Tristraguloolithus
  Tristraguloolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
  
  
• Youngoolithus
  Youngoolithus
  Youngoolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....