| Pachycorioolithus | |
|---|---|
Egg fossil classification  | |
| Oofamily: | † Pachycorioolithidae Lawver et al., 2016 |
| Oogenus: | † Pachycorioolithus Lawver et al., 2016 |
| Oospecies | |
| |
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. [1]
Pachycorioolithus is represented in the fossil record by a single, 80% complete fossil egg. It is elongated, measuring 50 mm (2.0 in) long by 32 mm (1.3 in) across, and smooth-surfaced. Thin pores (20 to 30 µm in diameter) cut through the eggshell. [1]
The eggshell is very thin, measuring only 166 µm thick, and is composed of three structural layers: the mammillary, continuous, and external layers. Pachycorioolithus is unique for having an external layer thicker than its continuous layer, with an external to continuous layer ratio of 1.6:1. This sets it apart from nearly all other known eggs. An unnamed Brazilian fossil egg also has an external layer thicker than continuous layer, but only barely thicker. Also, a few modern bird eggs have a similar, extremely thick external layer. These examples appear to result from convergent evolution, as they represent isolated cases in different clades. [1]
Based on its unique characteristics, Lawver et al. (2016) assigned Pachycorioolithus to its own monotypic oofamily, Pachycorioolithidae. [1]
Though no embryo was found in the egg, Pachycorioolithus can be referred to Theropoda by the characteristics of its eggshell. However, it is uncertain whether the parent was a bird or not. [1] Most non-avian dinosaurs have a two- or one-layered eggshell, whereas birds typically have a three-layered eggshell (like Pachycorioolithus). [2] However, most Mesozoic bird eggs have only two layers [1] and some non-avian dinosaur eggs have three layers, so this trait alone cannot be used to identify bird eggs. [3] Lawver et al. (2016) believed it likely that P. jinyunensis pertains to a bird because of its small size and extremely thin shell, but they could not exclude the possibility that it was laid by a small, non-avian, theropod. [1]
The only known P. jinyunensis specimen was discovered in a quarry near Shuhong, a town in Jinyun County in Zhejiang. This site is part of the Liangtoutang Formation, dating to the Albian. [1]
Pachycorioolithus was first described in 2016 by a team of paleontologists consisting of Daniel R. Lawver and Frankie D. Jackson of the Montana State University, Jin Xingsheng of the Zhejiang Museum of Natural History, and Wang Qiongying of the Jinyun Museum. It was based on a single egg specimen housed in the Jinyun Museum. They gave it the name Pachycorioolithus jinyunensis, from the Greek "pachys" (thick) and "corys" (helmet), a reference to its thick outer layer, combined with "oolithus", the standard suffix for oogenus names, meaning "stone egg". [1] The specific epithet means "from Jinyun", the county where it was found. [1]
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.
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.
Macroelongatoolithus is an oogenus of large, fossil theropod eggs. They are known from Asia and from North America.
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.
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. 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.
Parvoblongoolithus is an oogenus of fossil dinosaur egg whose small size and unusual shape suggest the possibility that it is a dwarf egg.
Microolithus is an oogenus of fossil bird egg from Wyoming, with preserved embryonic remains inside some of its specimens.
Styloolithus is an oogenus of highly distinctive fossil egg from the Upper Cretaceous Djadokhta Formation and the Barun Goyot Formation in Mongolia.
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.
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.
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.
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.
Arriagadoolithus is the oogenus of fossil eggs which includes the eggs of the alvarezsaurid Bonapartenykus. Fossils of the creature were found in Patagonia; it may have brooded on its eggs.
The Liangtoutang Formation, also referred to as the Laijia Formation is a geological formation located in Zhejiang, China. Its strata date back to the Albian to Cenomanian stages of the Cretaceous period. The lithology primarily consists of red sandstone.