| Styloolithus Temporal range: | |
|---|---|
 | |
| Two partial cluthces | |
Egg fossil classification  | |
| Oofamily: | incertae sedis |
| Oogenus: | † Styloolithus |
| Oospecies | |
| |
Styloolithus is an oogenus of highly distinctive fossil egg from the Upper Cretaceous Djadokhta Formation and the Barun Goyot Formation in Mongolia. [1]
The eggs of Styloolithus were first discovered in 1991 by Karol Sabath in an assemblage of fossil eggs in the Gobi Desert, and were described as "larger avian eggs". [2] They were considered classified as Gobioolithus major in 1996 by Mikhailov. [1] In 2015, Varracchio and Barta redefined G. major, and reclassified the "larger avian eggs" into an entirely new oogenus, Styloolithus.
The type specimen of Styloolithus is a fossil clutch of at least four eggs and associated adult remains (probably representing the parent). Several other fossil eggs are also known. The egg clutches are tightly packed together, like Prismatoolithus and Troodontid eggs, in contrast to the loosely scattered nests of enantiornithine birds. However, the eggs themselves are quite different from Troodontids, and the associated skeletal remains are similar to the enantiornithine Gobipteryx minuta (=Nanantius valifanovi). [1]
S. sabathi eggs are quite different from all other known fossil eggs of the Cretaceous. At 70 mm long and 32 mm across, they are larger than both oospecies of Gobioolithus , and more elongated. It can be distinguished from all non-avian dinosaur eggs by the thick third layer of the shell (possibly representing an external zone). It lacks shell ornamentation, unlike Elongatoolithus and Macroelongatoolithus . [1]
The eggs are interesting because of the possible presence of an external zone, the outer layer of the eggshell which is rare outside of bird eggs. [3] If correctly interpreted, this would prove that Styloolithus in fact represents bird eggs. However, it cannot be proven to have an external layer until its shell is examined by scanning electron microscopy. [1]
When they were first discovered in 1991, Styloolithus eggs (then unnamed) were described as bird eggs. [2] The three phylogenetic analyses performed by Varracchio and Barta (2015) were inconclusive as to whether it represented a bird or a non-avian theropod. However, it is most likely avian because it has an unornamented, thin shell that probably has three structural layers, a combination of characters unique to bird eggs. [1] Also, the bones found associated with the eggs seem to be avian. [1] [2]
The association of adult bones with Styloolithus eggs suggests intense parental care. [2] The tight egg clutches show that the incubation methods differed from that of Gobipteryx. Like Troodontids, the parents of Styloolithus probably sat on top of largely buried eggs. It is unknown whether S. sabathi was incubated by the father or the mother of the eggs. [1]
Byronosaurus is a genus of troodontid dinosaur from the Late Cretaceous Period of Mongolia.
Tochisaurus is a genus of small troodontid theropod dinosaur from the Late Cretaceous Period of Mongolia. The type species is Tochisaurus nemegtensis.
The Barun Goyot Formation is a geological formation dating to the Late Cretaceous Period. It is located within and is widely represented in the Gobi Desert Basin, in the Ömnögovi Province of Mongolia.
The Djadochta formation is a highly fossiliferous geological formation in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 million to 71 million years ago. The type locality is the Bayn Dzak locality, famously known as the Flaming Cliffs. Reptile and mammal remains are among the fossils recovered from the formation.
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.
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.
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.
Subtiliolithus is an oogenus of fossil egg from the Nemegt Formation of Mongolia and the Ohyamashimo Formation of Japan. The eggs are notable for a very thin eggshell. It contains three oospecies: S. hyogoensis, S. kachchhensis and S. microtuberculatus. They were originally classified as a distinct oofamily, Subtiliolithidae, but numerous similarities to Laevisoolithus have led to their reclassification as Laevisoolithid eggs. A complete skeleton of Nanantius valifanovi was found associated with Subtiliolithus eggshells, indicating that the oogenus represents eggs of enantiornithine birds.
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.
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.
Montanoolithus is an oogenus of fossil egg found in Montana and Alberta. They were probably laid by a dromaeosaur or a caenagnathid.
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.
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.
Nanhsiungoolithus is an oogenus of dinosaur egg from the late Cretaceous of China. It belongs to the oofamily Elongatoolithidae, which means that it was probably laid by an oviraptorosaur, though so far no skeletal remains have been discovered in association with Nanhsiungoolithus. The oogenus contains only a single described oospecies, N. chuetienensis. It is fairly rare, only being know from two partially preserved nests and a few eggshell fragments.
Harenadraco is an extinct genus of troodontid theropod dinosaurs from the Late Cretaceous Baruungoyot Formation of Mongolia. The genus contains a single species, H. prima, known from a fragmentary skeleton. Harenadraco represents the first troodontid known from the Baruungoyot Formation. Since members of this family are also known from the Nemegt and Djadochta Formations, the discovery of Harendraco indicates that troodontids were important faunal components of every formation within the Nemegt Basin.