| Microolithus Temporal range: | |
|---|---|
Egg fossil classification  | |
| Basic shell type: | Ornithoid |
| Morphotype: | Ornithoid-ratite |
| Oofamily: | † Medioolithidae |
| Oogenus: | † Microolithus Jackson, Varricchio & Corsini, 2013 |
| Oospecies | |
| |
Microolithus is an oogenus of fossil bird egg from Wyoming, with preserved embryonic remains inside some of its specimens. [1]
Fossil bird eggs from the Paleogene are rare in North America, and have only occasionally been examined microstructurally and compared to modern birds. [1] The specimens that would later be named Microolithus were collected in 1940 by the paleontologist R. W. Wilson. In 2013, paleontologists from Montana State University Frankie D. Jackson and David J. Varricchio teamed up with Joseph A. Corsini from Eastern Oregon University to analyze these specimens, which they assigned to a new oogenus and oospecies, Microolithus wilsoni. This would be only the second oogenus of Paleogene bird egg to be named in North America (the first being Incognitoolithus ). [1]
The known specimens of Microolithus were found in the Eocene Willwood Formation in Park County, Wyoming. [1]
Microolithus is, as its name suggests, a small egg; the smallest specimen is 37 mm (1.5 in) by 30 mm (1.2 in). Like all medioolithids, it is roughly spherical. The eggshell is 600 μm thick, and its outer surface is smooth and glossy, but this may be due to erosion. [1]
Its eggshell is composed of three structural layers. The outermost layer (the external layer) contacts the middle layer (the continuous layer), abruptly. [1] The continuous layer has squamatic texture obscuring the prism-shaped eggshell units. The innermost layer (the mammillary layer) makes up one-fourth of the eggshell's thickness, and has an abrupt but wavy boundary with the continuous layer. [1] The eggshell has circular pores with a density of 1.08 per square millimeter. [1]
Some Mircoolithus specimens have embryonic remains of long bones and possibly vertebra, but no useful characteristics for determining which bones or to what bird group they belong are preserved. The periosteum of these bones is somewhat porous. [1]
Microolithus is very similar to modern bird eggs, even more so than Metoolithus and the other known Paleogene bird eggs. It closely resembles modern neognaths, especially the sandhill crane. [1]
Because of the numerous similarities of Microolithus wilsoni to the German Medioolithus , they are classified together (along with Incognitoolithus) in the oofamily Medioolithidae. [1]
Dinosaur eggs are the organic vessels in which a dinosaur embryo develops. When the first scientifically documented remains of non-avian 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.
Lithornis is a genus of extinct paleognathous birds. Although Lithornis was able to fly well, their closest relatives are the extant tinamous and ratites.
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 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.
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.
Paraelongatoolithus is a late Cretaceous oogenus of Chinese fossil egg, classified in the oofamily Elongatoolithidae, which represents the eggs of oviraptorosaurs.
Metoolithus is an oogenus of fossil bird egg from Nebraska. It is known from a single, near-complete egg, as well as several eggshell fragments. They are small, and spheroid. They show a mix of avian and non-avian characteristics.
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.
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.
Incognitoolithus is an oogenus of medioolithid fossil bird egg. It is notable for bearing evidence of predation, possibly from a bird pecking the eggshell.
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.