Gobioolithus

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Gobioolithus
Temporal range: Campanian
~84–70  Ma
GobioolithusComparison.jpg
Gobioolithus major (left) compared to G. minor (right)
Egg fossil classification OOjs UI icon edit-ltr.svg
Basic shell type: Ornithoid
Morphotype:† Ornithoid-prismatic
Oofamily:† Gobioolithidae
Oogenus:† Gobioolithus
Mikhailov, 1996a
Oospecies
  • †G. minorMikhailov, 1996a (type)
  • †G. majorMikhailov, 1996a

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.

Contents

G. minor is unusual because it frequently is found with embryonic skeletons of the enantiornithine bird Gobipipus. These embryos have well-developed wings, which suggest they would be able to fly very soon after hatching, unlike most modern birds.

Description

Thin section of G. minor shell Gobioolithus minor section.jpg
Thin section of G. minor shell

Gobioolithus eggs are small and smooth-shelled. They are asymmetrically shaped, similar to many modern bird eggs, with one end pointier than the other. The two oospecies are distinguished mainly by their size: G. major ranges from 50 to 53.5 mm long and 25 to 32 mm across, with an eggshell thickness of 0.2-0.4 mm, [1] whereas G. minor is only 30–46 mm by 20–24 mm and 0.1-0.2 mm thick. [2]

The microstructure of Gobioolithus' eggshell has not been thoroughly studied, and heavy recrystallization of most specimens makes it difficult to examine the eggshell structure or pore system. [1] [3] The eggshell consists of two (or possibly three) structural layers. The inner layer, called the mammillary layer, is about half the thickness of the outer, or continuous, layer. On the outside, many specimens have a recrystallized outer layer. This could simply due to diagenesis or it could be a true external zone, [1] which is a third layer present in most bird eggs but is rare in non-avian dinosaurs. [4] However, a few specimens are unaffected by recrystallization. These do not have a third layer, but this does not rule out the possibility that the eggshell originally had a three layers since the external layer can easily separate from the rest of the eggshell. [5] These specimens also reveal an angusticanaliculate pore system, which means that the pores have a low density, and are long, narrow, and straight. [3] [6]

Styloolithus, another fossil enantiornithine egg from the Gobi, differs from Gobioolithus in that it is larger and has a thicker eggshell with a proportionately smaller mammillary layer. [1] Laevisoolithids, which are also eggs of enantiornithines, are also larger than Gobioolithus, but they have a much thicker mammillary layer. [7]

Embryos

A modern megapode chick (Alectura lathami) with well-developed wings, similar to the embryos in Gobioolithus. Brushturkeychik.jpg
A modern megapode chick ( Alectura lathami ) with well-developed wings, similar to the embryos in Gobioolithus.

Many Gobioolithus minor specimens contain embryonic remains of the enantiornithine genus Gobipipus. [7] The embryos have well-ossified skeletons, implying that they were at a late stage in development when they died. Their wings and shoulders are especially well-developed. Only the modern megapodes and the little tern exhibit a comparable degree of embryonic ossification in the arm and shoulder bones. It is likely that Gobipipus hatchlings, like megapodes and little terns, would be able to fly very soon after hatching. [8] [7]

No embryos are known from G. major eggs, [9] but they are usually assumed to have been laid by a similar type of bird. [7]

Nests

Gobioolithus eggs were probably laid in open nests on the banks of ephemeral rivers or lakes, which could frequently flood the nesting areas and bury the eggs. [3] [7] The distribution of the eggs suggests that they had a long-term colonial nesting site at the Khermeen Tsav locality in the Barun Goyot Formation. [10] [7] At the Bayn-Dzak locality, the eggs are typically arranged in clutches, whereas elsewhere they are scattered randomly, each oriented nearly vertically in the substrate. [3] The solitary eggs may have been laid and buried individually, similar to the nesting habits of modern megapodes. It is also possible that they were originally laid in clutches, but flooding separated them and deposited them vertically as the water level dropped. Water damage would also explain why Gobioolithus shells are frequently heavily recrystallized. [3] [7]

Classification

According to the parataxonomic system used to classify fossil eggs, Gobioolithus is classified in the oofamily Gobioolithidae, which, in turn, is classified in the prismatic morphotype (also called the neognath morphotype) of the ornithoid basic type. [10] A cladistic analysis performed by Varricchio and Barta (2015) (pictured below) found Gobioolithus to be a sister taxon to Styloolithus. However, they considered Styloolithus different enough from Gobioolithus to warrant its exclusion from Gobioolithidae. [1]

Prismatoolithus gebiensis

Protoceratopsidovum sincerum

Parvoolithus tortuosus

Neognath eggs

Paleognath eggs

Gobioolithus minor

Styloolithus sabathi

Distribution

Gobioolithus is found in the Gobi Desert in Mongolia. More specifically, the fossils are found in the Barun Goyot and the Djadokhta Formations of the Nemegt Basin, which is dated to the Upper Cretaceous. [2] [1]

History

Numerous fossils, including Gobioolithus specimens, were discovered and collected by the Polish-Mongolian fossil-hunting expeditions in the Gobi Desert from 1963 to 1971 and by the Soviet-Mongolian expeditions between 1969 and 1996. These fossils were brought to the Institute of Paleobiology of the Polish Academy of Sciences in Warsaw and to the Paleontological Institute of the Russian Academy of Sciences in Moscow. [3] [11] Eggs now classified as Gobioolithus were first analyzed in 1981 by the Polish paleontologist Andrzej Elżanowski, who described several well-developed bird embryos within some of the fossil eggs housed in Warsaw. He identified them as most similar to Gobipteryx minuta , [8] so scientists began referring to them as "Gobipteryx eggs". [2]

In 1991, the Russian paleontologist Konstantin Mikhailov introduced the modern parataxonomic system used to classify fossil eggs. While he did not give the "Gobipteryx" eggs a formal name under this classification scheme, he did assign them to the prismatic morphotype in the ornithoid basic type. He believed that they were eggs of volant paleognaths, but probably not Gobipteryx (which was then considered to be a paleognath). [10] In the same year, the Polish paleontologist Karol Sabath reviewed the entire collection of fossil eggs discovered on the Polish expeditions, including the not-yet-named Gobioolithus eggs. Following Elżanowski, he referred them to Gobipteryx, though only tentatively because at the time ongoing studies of similar eggs found on the Soviet expeditions cast doubt on this classification. [11]

In 1994, Mikhailov, working with Sabath and Kurzanov, divided the Mongolian "Gobipteryx" eggs into two informal groups: G1, containing the smaller eggs (including the ones with embryos described by Elżanowski), and G2 for the larger eggs. [3] Two years later, Mikhailov went on to classify these eggs parataxonomically as a new oofamily, Gobioolithidae, containing the single oogenus Gobioolithus, with two oospecies: G. minor and G. major, corresponding to G1 and G2, respectively. [2] In 2013, Kurochkin, Chatterjee, and Mikhailov described a new genus and species of bird, Gobipipus reshetovi, based on the embryos within Gobioolithus eggs. They classified Gobipipus as an enantiornithine. [7] In 2015, some of the larger egg specimens previously assigned to G. major were moved into their own new oogenus and oospecies, Styloolithus sabathi. [1]

Related Research Articles

<span class="mw-page-title-main">Enantiornithes</span> Extinct clade of dinosaurs

The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans, the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. Over eighty species of Enantiornithes have been named, but some names represent only single bones, so it is likely that not all are valid. The Enantiornithes became extinct at the Cretaceous–Paleogene boundary, along with Hesperornithes and all other non-avian dinosaurs.

<i>Gobipteryx</i> Extinct genus of birds

Gobipteryx is a genus of prehistoric bird from the Campanian Age of the Late Cretaceous Period. It is not known to have any direct descendants. Like the rest of the enantiornithes clade, Gobipteryx is thought to have gone extinct near the end of the Cretaceous.

<span class="mw-page-title-main">Barun Goyot Formation</span> Geological formation in Mongolia

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.

<i>Elongatoolithus</i> Fossil dinosaur eggs

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.

<i>Dendroolithus</i> Oogenus of dinosaur egg

Dendroolithus is an oogenus of Dendroolithid dinosaur egg found in the late Cenomanian Chichengshan Formation, in the Gong-An-Zhai and Santonian Majiacun Formations of China and the Maastrichtian Nemegt and Campanian Barun Goyot Formation of Mongolia. They can be up to 162 mm long and 130 mm wide. These eggs may have been laid by a Therizinosaur, Sauropod, or Ornithopod. The oospecies "D." shangtangensis was originally classified as Dendroolithus, however, it has since been moved to its own distinct oogenus, Similifaveoloolithus. This oogenus is related with embryos of the theropod Torvosaurus

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.

<i>Macroelongatoolithus</i> Oogenus of dinosaur egg

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.

<i>Macroolithus</i> Oogenus of dinosaur egg

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.

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.

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.

<span class="mw-page-title-main">Egg fossil</span> Fossilized remains of eggs laid by ancient animals

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.

Microolithus is an oogenus of fossil bird egg from Wyoming, with preserved embryonic remains inside some of its specimens.

<i>Styloolithus</i> Oogenus of fossil egg

Styloolithus is an oogenus of highly distinctive fossil egg from the Upper Cretaceous Djadokhta Formation and the Barun Goyot Formation in Mongolia.

<span class="mw-page-title-main">Elongatoolithidae</span> Oofamily of dinosaur eggs

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.

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.

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.

References

  1. 1 2 3 4 5 6 7 Varricchio, David J.; Barta, Daniel E. (2015). "Revistiting Sabath's "Larger Avian Eggs" from the Gobi Cretaceous". Acta Palaeontologica Polonica. 60 (1): 11–25. doi: 10.4202/app.00085.2014 .
  2. 1 2 3 4 Mikhailov, Konstantin (1996). "Bird Eggs in the Upper Cretaceous of Mongolia". Paleontological Journal. 30 (1): 114–116.
  3. 1 2 3 4 5 6 7 Mikhailov, Konstantin; Sabath, Karol; Kurzanov, Sergey (1994). "Eggs and nests from the Cretaceous of Mongolia". In Carpenter, Kenneth; Hirsch, Karl F.; Horner, John R. (eds.). Dinosaur eggs and babies. Cambridge University Press. pp. 88–115. ISBN   978-0-521-44342-5.
  4. ↑ Wilson, Laura E.; Chin, Karen; Jackson, Frankie D.; Bray, Emily S. "II. Eggshell morphology and structure". UCMP Online Exhibits: Fossil Eggshell. Retrieved 16 April 2016.
  5. ↑ Mikhailov, Konstantin (2014). "Eggshell structure, parataxonomy, and phylogenetic analysis: some notes on articles published from 2002 to 2011". Historical Biology. 26 (2): 144–154. Bibcode:2014HBio...26..144M. doi:10.1080/08912963.2013.829824. S2CID   84878973.
  6. ↑ Carpenter, Kenneth (1999). "How to Study a Fossil Egg". Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past) . Bloomington, Indiana: Indiana University Press. pp.  122–144. ISBN   978-0-253-33497-8.
  7. 1 2 3 4 5 6 7 8 Kurochkin, Evgeny; Chatterjee, Sankar; Mikhailov, Konstantin (2013). "An embryonic enantiornithine bird and associated eggs from the Cretaceous of Mongolia". Paleontological Journal. 47 (11): 1252–1269. Bibcode:2013PalJ...47.1252K. doi:10.1134/s0031030113110087. S2CID   86747842.
  8. 1 2 Elżanowski, Andrzej (1981). "Embryonic Bird Skeletons From the Late Cretaceous of Mongolia" (PDF). Palaeontologia Polonica. 42: 147–179. Archived from the original (PDF) on 2016-04-12. Retrieved 2016-04-10.
  9. ↑ Varricchio, D.J.; Jackson, F.D. (2004). "A phylogenetic assessment of prismatic dinosaur eggs from the Cretaceous Two Medicine Formation of Montana". Journal of Vertebrate Paleontology. 24 (4): 931–937. doi:10.1671/0272-4634(2004)024[0931:apaopd]2.0.co;2. S2CID   85987939.
  10. 1 2 3 Mikhailov, Konstantin E. (1991). "Classification of fossil eggshells of amniotic vertebrates". Acta Palaeontologica Polonica. 36 (2): 193–238.
  11. 1 2 Sabath, Karol (1991). "Upper Cretaceous amniotic eggs from the Gobi Desert" (PDF). Acta Palaeontologica Polonica. 36 (2): 151–192.
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