Elongatoolithidae

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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
Zhao, 1975
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]

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

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.[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 "

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

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

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

Ornitholithus, Paraelongatoolithus, Undulatoolithus,[1] and Rodolphoolithus.[19] Also, Porituberoolithus and Continuoolithus are occasionally included in Elongatoolithidae.[20]

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. ^ 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. ^ a b 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. hdl:1807/81388.[permanent dead link
    ]
  9. ^ a b 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. ^ 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.
  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. ^ 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.
  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

External links

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