Elongatoolithidae

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Elongatoolithidae
Temporal range: Cretaceous-Paleocene
Academy of Natural Sciences, Philadelphia - IMG 7450.JPG
Elongatoolithid eggs in the Academy of Natural Sciences, Philadelphia
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Basic shell type: Ornithoid
Morphotype: Ornithoid-ratite
Oofamily:† Elongatoolithidae
Zhao, 1975
Oogenera

Elongatoolithidae is an oofamily of fossil eggs, representing the eggs of oviraptorosaurs (with the exception of the avian Ornitholithus ). They are known for their highly elongated shape. Elongatoolithids have been found in Europe, Asia, and both North and South America. [1]

Contents

Distribution

Elongatoolithids have a very broad distribution. They have been found across Asia and the US, as well as in Spain, France, and Argentina, with ages ranging from lower Cretaceous to the Paleocene. [1]

Description

Elongatoolithids are, as their name suggests, highly elongated eggs; they are at least twice as long as they are wide. [2] They vary widely in size, ranging from the 7 cm long Elongatoolithus chichengshanensis to the gigantic 60 cm Macroelongatoolithus. All known clutches are laid in concentric circles of paired eggs, sometimes in up to three superimposed layers. [1]

Elongatoolithid eggshells are made up of two layers: The inner layer, called the mammillary layer or the cone layer, is made up of radiating calcite crystals. The outer layer is distinctive for not being divided into well-defined shell units, and hence it is called the continuous layer or the cryptoprismatic layer. The boundary between the two layers is abrupt, but wavy. Typically, elongatoolithid eggs have an angusticanaliculate pore system, meaning the pores are thin, straight, and unbranching. The surface ornamentation of the eggshells varies from scattered nodes (dispersituberculate) to linear ridges (lineartuberculate), occasionally with nodes in long irregular chains (ramotuberculate). [1]

History

An elongatoolithid with embryo preserved inside Citipati embryo.jpg
An elongatoolithid with embryo preserved inside

The first elongatoolithid eggs were discovered in the 1920s, and were thought to belong to Protoceratops . [3] Oviraptor was first discovered in 1924 with a nest of elongatoolithid eggs, and it was conjectured to have been caught in the act of raiding a Protoceratops nest. [4] Following the discovery of Troodon eggs in 1990, their close resemblance to elongatoolithids lead Russian paleontologist Konstantin Mikhailov to believe they were actually theropod eggs, not Protoceratops eggs. [2] In 1994, his hypothesis was confirmed when Norell et al. discovered embryonic remains of an Oviraptorosaur inside an elongatoolithid egg. It was then hypothesized that Oviraptor was in fact a brooding mother, not an egg thief. [5] Since then, several discoveries of embryos and association of adults with eggs have shown that elongatoolithids are the eggs of Oviraptorosaurs. [1]

The first oospecies formally described was "Oolithes" elongatus (Young, 1954), from China. They were thought to belong to Protoceratops or a related dinosaur because of their similarity to the supposed Protoceratops eggs found in Mongolia. [6] In 1975, Chinese paleontologist Zhao Zikui devised a formal classification system for fossil eggs, in which he created a new oogenus for "Oolithes" elongatus: Elongatoolithus . He classified Elongatoolithus and another new oogenus Macroolithus into a new oofamily, Elongatoolithidae. [7]

The oogenus Spongioolithus, first named by Bray in 1999, was originally considered a member of Elongatoolithidae, but it is currently considered a junior synonym of the non-elongatoolithid Continuoolithus . [8]

Paleobiology

Citipati parent sitting on its nest of elongatoolithid eggs Citipati IGM 100 979.jpg
Citipati parent sitting on its nest of elongatoolithid eggs

Elongatoolithids are known to be the eggs of oviraptorosaurs (except for the avian Ornitholithus). [1] Several oviraptorosaurs have been found in association with elongatoolithid eggs, [9] including some specimens still inside the mother. [10] [11] Fossil embryos found inside elongatoolithid eggs have also been identified as oviraptorosaurian. [5] [12] [13]

Several oviraptorosaurs, like Nemegtia , Citipati , Oviraptor , and cf. Machairasaurus , have been found sitting on top of their nests. [9] [14] All of them have their arms spread out over the eggs in a bird-like posture, and the parent's body would effectively cover the entire nest. [14] This indicates intensive parental care of the eggs. It is not certain whether the specimens found brooding are male or female, but the examined limb bones of a brooding Citipati show none of the evidence of egg-laying that would be expected if theropods took phosphorus and calcium from long bone tissues (like crocodylians) or medullary bone (like birds), suggesting it was a male. Also, the clutches were proportionally large compared to the size of the adult, which suggests a polygamous system, similar to modern paleognaths, in which multiple females contribute eggs to a single nest which is then cared for by the father. [15]

The eggs are laid in pairs, as shown by the discovery of two Macroolithus eggs simultaneously within the mother, and the pairing of eggs within nests. This shows that oviraptorosaurs had two functional oviducts (unlike birds, which have only one), and would produce two eggs at a time. Also, the relatively large size of the eggs indicates that a female could not lay more than one pair at a time. [10]

Parataxonomy

In the basic-type and morphotype scheme for eggshell classification (which is now typically disused [16] [17] ), elongatoolithids are of the Ornithoid basic type and Ornithoid-Ratite morphotype. [2] They are similar to the Troodon eggshells, [2] which are now classified in the oofamily Prismatoolithidae. [18]

Elongatoolithidae contains the oogenera Nanhsiungoolithus , Elongatoolithus , Macroolithus , Macroelongatoolithus , Ellipsoolithus , Trachoolithus , Heishanoolithus , Ornitholithus , Paraelongatoolithus , Undulatoolithus , [1] and Rodolphoolithus . [19] Also, Porituberoolithus and Continuoolithus are occasionally included in Elongatoolithidae. [20]

Related Research Articles

<span class="mw-page-title-main">Oviraptoridae</span> Extinct family of dinosaurs

Oviraptoridae is a group of bird-like, herbivorous and omnivorous maniraptoran dinosaurs. Oviraptorids are characterized by their toothless, parrot-like beaks and, in some cases, elaborate crests. They were generally small, measuring between one and two metres long in most cases, though some possible oviraptorids were enormous. Oviraptorids are currently known only from the Late Cretaceous of Asia, with the most well-known species and complete specimens found only in the Gobi Desert of Mongolia and northwestern China.

<i>Gigantoraptor</i> Extinct genus of dinosaurs

Gigantoraptor is a genus of large oviraptorosaur dinosaur that lived in Asia during the Late Cretaceous period. It is known from the Iren Dabasu Formation of Inner Mongolia, where the first remains were found in 2005.

<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.

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.

<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.

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.

<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.

Montanoolithus is an oogenus of fossil egg found in Montana and Alberta. They were probably laid by a dromaeosaur or a caenagnathid.

<span class="mw-page-title-main">Timeline of oviraptorosaur research</span>

This timeline of oviraptorosaur research is a chronological listing of events in the history of paleontology focused on the oviraptorosaurs, a group of beaked, bird-like theropod dinosaurs. The early history of oviraptorosaur paleontology is characterized by taxonomic confusion due to the unusual characteristics of these dinosaurs. When initially described in 1924 Oviraptor itself was thought to be a member of the Ornithomimidae, popularly known as the "ostrich" dinosaurs, because both taxa share toothless beaks. Early caenagnathid oviraptorosaur discoveries like Caenagnathus itself were also incorrectly classified at the time, having been misidentified as birds.

Heishanoolithus is an oogenus of Elongatoolithid fossil egg from the Shahai Formation in Liaoning. It is known only from seven eggshell fragments. It is most notable for having a very thin eggshell, the dense covering of nodes on the eggshell surface, and for its relatively thin mammilary layer. While no remains of Heishanoolithus have been associated with skeletal remains, strong evidence links Elongatoolithid eggs to Oviraptorosaurs.

Undulatoolithus is an oogenus of Chinese fossil dinosaur egg belonging to Elongatoolithidae. It is very similar to Macroolithus, but has different ornamentation. Like other elongatoolithids, it was probably laid by oviraptorosaurs.

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.

Tubercuoolithus is an oogenus of dinosaur egg from the early Campanian of Montana.

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.

<i>Gobioolithus</i> Fossil bird egg native to Mongolia

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.

<i>Beibeilong</i> Caenagnathid dinosaur genus from the Late Cretaceous

Beibeilong is a genus of large caenagnathid dinosaurs that lived in China during the Late Cretaceous epoch, about 96 million to 88 million years ago. The genus contains a single species, Beibeilong sinensis. The species was named and described in 2017 through analysis of an embryonic skeleton and partial nest with large eggs that were discovered in the Gaogou Formation of China between 1992 and 1993.

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 Simon, D. J. (2014). "Giant Dinosaur (theropod) Eggs of the Oogenus Macroelongatoolithus (Elongatoolithidae) from Southeastern Idaho: Taxonomic, Paleobiogeographic, and Reproductive Implications." (Doctoral dissertation, Montana State University, Bozeman).
  2. 1 2 3 4 Mikhailov, K. (1991) "Classification of fossil eggshells of amniotic vertebrates" Acta Palaeontologica Polonica 36(2): 193–238.
  3. ↑ VanStraelen V. (1925). "The Microstructure of the Dinosaurian Eggshells from the Cretaceous Beds of Mongolia." American Museum Novitates No. 173.
  4. ↑ Osborn, H.F. (1924) "Three new theropoda, protoceratops zone, central Mongolia." American Museum Novitates 144.
  5. 1 2 Norell, Mark A., James M. Clark, Dashzeveg Demberelyin, Barsbold Rhinchen, Luis M. Chiappe, Amy R. Davidson, Malcolm C. McKenna, Perle Altangerel, and Michael J. Novacek. (1994) "A theropod dinosaur embryo and the affinities of the Flaming Cliffs dinosaur eggs." Science 266(5186): 779–782.
  6. ↑ Young, C. 1954. "Fossil reptilian eggs from Laiyang, Shantung, China." Scientia Sinica 3(4):505–522
  7. ↑ Zhao Z.K. (1975) "The microstructures of the dinosaurian eggshells of Nanxiong Basin, Guandong province. (1) On the classification of dinosaur eggs." Vertebrata PalAsiatica 13(2):105–117 (in Chinese)
  8. ↑ Voris, Jared T.; Zelenitsky, Darla K.; Therrien, Francois; Tanaka, Kohei (2018). "Dinosaur eggshells from the lower Maastrichtian St. Mary River Formation of southern Alberta, Canada". Canadian Journal of Earth Sciences. 55 (3): 272–282. Bibcode:2018CaJES..55..272V. doi:10.1139/cjes-2017-0195. hdl: 1807/81388 .[ permanent dead link ]
  9. 1 2 Fanti F., Currie P.J., Badamgarav D. (2012) "New specimens of Nemegtomaia from the Baruungoyot and Nemegt Formations (Late Cretaceous) of Mongolia." PLOS One 7(2).
  10. 1 2 Sato T., Cheng Y.N., Wu X.C., Zelenitsky D.K., Hsiao Y.F. (2005) "A pair of shelled eggs inside a female dinosaur." Science 308:375.
  11. ↑ He T., Varricchio D.J., Jackson F.D., Jin X., Poust A.W. (2012) "An Oviraptorid Adult-Egg Association and the Origin of Avialan Reproductive Strategies." Programs and Abstracts of the 72nd Annual Meeting of the Society of Vertebrate Paleontology: 108.
  12. ↑ Weishampel D.B., Fastovsky D.E., Watabe M., Varricchio D., Jackson D., Tsogtbaatar K., and Barsbold R. (2008) "New oviraptorid embryos from Bugin-tsav, Nemegt Formation (Upper Cretaceous), Mongolia, with insights into their habit and growth." Journal of Vertebrate Paleontology 28(4):1110–1119.
  13. ↑ Cheng Y.N., Qiang J.I., Wu X.C., Shan H.Y. (2008) "Oviraptorosaurian eggs (Dinosauria) with embryonic skeletons discovered for the first time in China." Acta Geologica Sinica 82(6): 1089–1094
  14. 1 2 Clark, J.M., Norell, M.A., & Chiappe, L.M. (1999). "An oviraptorid skeleton from the Late Cretaceous of Ukhaa Tolgod, Mongolia, preserved in an avianlike brooding position over an oviraptorid nest." American Museum Novitates, 3265.
  15. ↑ Varricchio DJ, Moore JR, Erickson GM, Norell MA, Jackson FD, Borkowski JJ. (2008) "Avian paternal care had dinosaur origin." Science, 322(5909): 1826–1828.
  16. ↑ Zelenitsky, D. K., and Therrien, F. (2008). "Phylogenetic analysis of reproductive traits of maniraptoran theropods and its implications for egg parataxonomy." Palaeontology , 51(4): 807–816.
  17. ↑ Grellet-Tinner, G., and Norell, M. (2002). "An avian egg from the Campanian of Bayn Dzak, Mongolia." Journal of Vertebrate Paleontology , 22(3): 719–721.
  18. ↑ Varricchio, D. J., Horner, J. R., and Jackson, F. D. (2002). "Embryos and eggs for the Cretaceous theropod dinosaur Troodon formosus." Journal of Vertebrate Paleontology, 22(3): 564–576.
  19. ↑ Vianey-Liaud, M., & Garcia, G. (2003). "Diversity among North African dinosaur eggshells." Palaeovertebrata, 32(2–4), 171–188.
  20. ↑ Q. Wang, X.-L. Wang, Z.-K. Zhao and Y.-G. Jiang. 2010. "A new oogenus of Elongatoolithidae from the Upper Cretaceous Chichengshan Formation of Tiantai Basin, Zhejiang Province." Vertebrata PalAsiatica 48(2):111–118
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