| Sankofa | |
|---|---|
Egg fossil classification  | |
| Basic shell type: | † Dinosauroid-prismatic |
| Oofamily: | † Prismatoolithidae |
| Oogenus: | †Sankofa López-Martínez & Vicens, 2012 |
| Oospecies | |
| |
Sankofa is an oogenus of prismatoolithid egg. They are fairly small, smooth-shelled, and asymmetrical. Sankofa may represent the fossilized eggs of a transitional species between non-avian theropods and birds. [1]
The name Sankofa comes from the Ashante word "sankofa", meaning 'learning from the past', symbolized by a bird with an egg in its bill. The oospecific epiphet pyrenaica refers to the Pyrenees, where the eggs were first discovered. [1]
Sankofa pyrenaica is known solely from the Aren Formation, in the southern Pyrenees of Catalonia, Spain, dating from the Upper Campanian to Lower Maastrichtian. [1]
Sankofa eggs are uniformly 7 cm long and 4 cm wide, and their eggshell averages 0.27 mm thick. The eggshell consists of two layers, the prismatic (or palisade) layer and the mammillary layer, similar to most other non-avian dinosaur eggshells. [2] In Sankofa, these two layers have a gradual boundary, and the mammillary layer is much thinner than the prismatic. The prismatic has a slightly squamatic microstructure, very similar to the eggs of Troodon and other prismatoolithids, a step towards the fully squamatic texture of bird eggs. The eggshell has a smooth surface with no trace of ornamentation, and highly variable pore density. [1]
The most significant characteristic of Sankofa is its shape: they are asymmetric, with an ovoid shape, like bird eggs. A morphometric analysis by López-Martínez and Vicens in 2012 found that it was an intermediate shape between avian and non-avian theropods, and also very similar to an enantiornithine egg from the Bajo de la Carpa Formation in Argentina, though their microstructures are quite different. [1]
Parataxonomically, Sankofa is classified in the oofamily Prismatoolithidae, because of its microstructure. Cladistic analysis found Sankofa to be in a polytomy with Protoceratopsidovum , Troodon eggs, and birds. The mosaic of avian and non-avian characteristics makes it uncertain whether S. pyrenaica was laid by a bird or a non-avian theropod, and provides further evidence for the theory that birds evolved from dinosaurs. [1] It probably represents a transitional form between the two groups. [1]
Dinosaur eggs are the organic vessels in which a dinosaur embryo develops. When the first scientifically documented remains of dinosaurs were being described in England during the 1820s, it was presumed that dinosaurs had laid eggs because they were reptiles. In 1859, the first scientifically documented dinosaur egg fossils were discovered in France by Jean-Jacques Poech, although they were mistaken for giant bird eggs. The first scientifically recognized dinosaur egg fossils were discovered in 1923 by an American Museum of Natural History crew in Mongolia. Since then many new nesting sites have been found all over the world and a system of classification based on the structure of eggshell was developed in China before gradually diffusing into the West. Dinosaur eggshell can be studied in thin section and viewed under a microscope. The interior of a dinosaur egg can be studied using CAT scans or by gradually dissolving away the shell with acid. Sometimes the egg preserves the remains of the developing embryo inside. The oldest known dinosaur eggs and embryos are from Massospondylus, which lived during the Early Jurassic, about 190 million years ago.
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.
Protoceratopsidovum is an oogenus of dinosaur egg from Mongolia. Despite its name, it does not represent the eggs of a protoceratopsid, but rather the eggs of maniraptoran theropods.
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.
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.
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 era. 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.
Prismatoolithidae is an oofamily of fossil eggs. They may have been laid by ornithopods or theropods.
Montanoolithus is an oogenus of fossil egg found in Montana and Alberta. They were probably laid by a dromaeosaur or a caenagnathid.
Reptile egg fossils are the fossilized remains of eggs laid by 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. Some ancient reptiles are known to have given live birth and are therefore not anticipated to have left behind egg fossils.
Parvoblongoolithus is an oogenus of fossil dinosaur egg whose small size and unusual shape suggest the possibility that it is a dwarf egg.
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.
Tubercuoolithus is an oogenus of dinosaur egg from the early Campanian of Montana.
Triprismatoolithus is an oogenus of dinosaur egg native to Teton County, Montana. It is classified in the oofamily Arriagadoolithidae, the eggs of alvarezsaurs.
Nipponoolithus is an oogenus of fossil egg native to Japan. It is one of the smallest known dinosaur eggs, and was probably laid by some kind of non-avian maniraptor.
Trigonoolithus is an oogenus of dinosaur egg, representing a basal prismatoolithid. Its eggshell, like avian eggs, is composed of three structural layers, but cladistic analysis suggests that its parent was a non-avian theropod.
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.
Pachycorioolithus is an oogenus of small, thin-shelled fossil egg from the early Cretaceous in China. It probably belongs to a bird, though there is a possibility the parent was a non-avian theropod. It was named in 2016, based on a single specimen found in Zhejiang.
Plagioolithus is an oogenus of fossil egg. It is from the Early Cretaceous of Japan. It was probably laid by a bird, making it the oldest known fossil bird egg.