User:Ashorocetus/sandbox/Elongatoolithidae

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Ashorocetus/sandbox/Elongatoolithidae
Temporal range: Cretaceous-Paleocene
Elongatoolithid eggs in the Academy of Natural Sciences, Philadelphia
Egg fossil classification Edit this classification
Basic shell type: Ornithoid
Morphotype:
Ornithoid-ratite
Oofamily: †Elongatoolithidae
Oogenera

Elongatoolithidae is an

Ornitholithus). They are known for their highly elongated shape. Elongatoolithids have been found in Europe, Asia, and both North and South America.[1]

Distribution

Elongatoolithids have a very broad distribution. They have been found across

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.

clutches are laid in concentric circles of paired eggs, sometimes in up to three superimposed layers.[1]

Eggshell

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 is varies from scattered nodes (dispersituberculate) to linear ridges (lineartuberculate), occasionally with nodes in long irregular chains (ramotuberculate).[1]

Nests

Coloration

The presence of pigments in the eggshells of three specimens of the elongatoolithid Macroolithus yaotunensis indicates that these eggs were a blue-green color. The preserved fossil pigments (

protoporphyrin) are the same pigments found in modern bird eggs, strongly suggesting homology. In modern birds, the coloration can act as camouflauge or, in some species, as a post-mating sexual signal. Eggshell coloration is also correlated with paternal care.[3]

History

See also: Timeline of egg fossil research
An elongatoolithid with embryo preserved inside

The first elongatoolithid eggs were discovered in the 1920s, and were thought to belong to

Oviraptorosaur inside an elongatoolithid egg. It was then hypothesized that Oviraptor was in fact a brooding mother, not an egg thief.[6] Since then, several discoveries of embryos and association of adults with eggs have shown that elongatoolithids are the eggs of Oviraptorosaurs.[1]

Prior to the advent of modern eggshell parataxonomy, the Chinese paleontologist

formal classification system for fossil eggs. He created the oogenus Macroolithus for Yang's O. rugustus, Elongatoolithus for most O. elongatus specimens, and Nanhsiungoolithus for two other specimens of "O." elongatus[9]

Nesting and Parental Care

Citipati parent sitting on its nest of elongatoolithid eggs

Elongatoolithids are known to be the eggs of oviraptorosaurs (except for the avian Ornitholithus, which is occasionally considered an elongatoolithid).[1] Several oviraptorosaurs have been found in association with elongatoolithid eggs,[10] including some specimens still inside the mother.[11][12] Fossil embryos found inside elongatoolithid eggs have also been identified as oviraptorosaurian.[6][13][14]

Several oviraptorosaurs, like

paleognaths, in which multiple females contribute eggs to a single nest which is then cared for by the father.[16] Smaller oviraptorosaurs would have sat directly on the eggs, similar to modern birds. Larger species, on the other hand, show a unique adaptation to place most of their weight on the raised center of the nest, rather than on the eggs.[17]

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.[11]

Elongatoolithid nests were probably typically incubated above ground, instead of being buried under substrate or vegetation like some other types of dinosaur eggs.[18] Some authors in the past have argued that elongatoolithids such as Elongatoolithus and Macroolithus were buried, which would explain the high porosity of the eggshells.[19][20] Deeming (2006) noticed the incongruence of this hypothesis with the evidence of brooding in Oviraptor and Troodon, and suggested that these dinosaurs merely sat atop a buried nest.[20] However, a statistical analysis of eggshell porosity in 2015 by Tanaka et al. found that elongatoolithids would have been laid in open nests, with the possible exception of Elongatoolithus elongatus.[18]

Parataxonomy

In the basic-type and morphotype scheme for eggshell classification (which is now typically disused[21][22]), 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.[23]

Elongatoolithidae contains the oogenera

Spongioolithus.[25] Also, Porituberoolithus and Continuoolithus are occasionally included in Elongatoolithidae.[26]

References

  1. ^ a b c d e f g 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. ^ a b c d Mikhailov, K. (1991) "Classification of fossil eggshells of amniotic vertebrates" Acta Palaeontologica Polonica 36(2): 193–238.
  3. doi:/doi.org/10.7717/peerj.3706. {{cite journal}}: Check |doi= value (help
    )
  4. ^ VanStraelen V. (1925). "The Microstructure of the Dinosaurian Eggshells from the Cretaceous Beds of Mongolia." American Museum Novitates No. 173.
  5. ^ Osborn, H.F. (1924) "Three new theropoda, protoceratops zone, central Mongolia." American Museum Novitates 144.
  6. ^
    Science
     266(5186): 779–782.
  7. ^ Yang, Zhongjian (1954). "Fossil Reptilian Eggs from Laiyang, Shantung, China". Scientia Sinica. 3: 505–522.
  8. ^ Yang, Zhongjian (1965). "Fossil eggs from Nanhsiung, Kwangtun and Kanchou, Kiangsi" (PDF). Vertebrata PalAsiatica. 9 (2): 141–170.
  9. Vertebrata PalAsiatica
     13(2):105–117 (in Chinese)
  10. ^
    PLoSONE
    7(2).
  11. ^ a b 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.
  12. ^ 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.
  13. ^ 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.
  14. ^ 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
  15. ^ a b 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.
  16. doi:10.1126/science.1163245
    .
  17. doi:10.1098/rsbl.2018.0135
    .
  18. ^
    doi:10.1371/journal.pone.0142829.{{cite journal}}: CS1 maint: unflagged free DOI (link
    )
  19. ^ Mou, Yun (1992). "Nest Environments of the Late Cretaceous Dinosaur eggs from Nanxiong Basin, Guangdong Province" (PDF). Vertebrata PalAsiatica. 30 (2): 120–134.
  20. ^
    doi:10.1111/j.1475-4983.2005.00536.x
    .
  21. ^ 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.
  22. ^ 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.
  23. ^ 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.
  24. ^ Vianey-Liaud, M., & Garcia, G. (2003). "Diversity among North African dinosaur eggshells." Palaeovertebrata, 32(2–4), 171–188.
  25. ^ E. S. Bray. (1999) "Eggs and eggshell from the Upper Cretaceous North Horn Formation, central Utah." Vertebrate Paleontology in Utah, Utah Geological Survey Miscellaneous Publication 99-1:361–375
  26. ^ 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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