Elongatoolithidae

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]

Elongatoolithidae
Temporal range: Cretaceous-Paleocene
Academy of Natural Sciences, Philadelphia - IMG 7450
Elongatoolithid eggs in the Academy of Natural Sciences, Philadelphia
Egg fossil classification
Basic shell type: Ornithoid
Morphotype: Ornithoid-ratite
Oofamily: Elongatoolithidae
Oogenera

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

History

Citipati embryo
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]

Paleobiology

Citipati IGM 100 979
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,[8] including some specimens still inside the mother.[9][10] Fossil embryos found inside elongatoolithid eggs have also been identified as oviraptorosaurian.[5][11][12]

Several oviraptorosaurs, like Nemegtia, Citipati, Oviraptor, and cf. Machairasaurus, have been found sitting on top of their nests.[8][13] 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.[13] 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.[14]

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.[9]

Parataxonomy

In the basic-type and morphotype scheme for eggshell classification (which is now typically disused[15][16]), 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.[17]

Elongatoolithidae contains the oogenera Nanhsiungoolithus, Elongatoolithus, Macroolithus, Macroelongatoolithus, Ellipsoolithus, Trachoolithus, Heishanoolithus, Ornitholithus, Paraelongatoolithus, Undulatoolithus,[1] Rodolphoolithus,[18] and Spongioolithus.[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. ^ a b Fanti F., Currie P.J., Badamgarav D. (2012) "New specimens of Nemegtomaia from the Baruungoyot and Nemegt Formations (Late Cretaceous) of Mongolia." PLoSONE 7(2).
  9. ^ 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.
  10. ^ 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.
  11. ^ 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.
  12. ^ 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
  13. ^ 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.
  14. ^ Varricchio DJ, Moore JR, Erickson GM, Norell MA, Jackson FD, Borkowski JJ. (2008) "Avian paternal care had dinosaur origin." Science, 322(5909): 1826–1828.
  15. ^ 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.
  16. ^ 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.
  17. ^ 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.
  18. ^ Vianey-Liaud, M., & Garcia, G. (2003). "Diversity among North African dinosaur eggshells." Palaeovertebrata, 32(2–4), 171–188.
  19. ^ 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
  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

Ageroolithus

Ageroolithus is an oogenus of dinosaur egg. It may have been laid by a theropod.

Continuoolithus

Continuoolithus is an oogenus (fossil egg genus) of dinosaur egg found in the late Campanian of Alberta and Montana. It was laid by an unknown type of theropod. These small eggs (measuring 77–123 mm (3.0–4.8 in) long) are similar to the eggs of oviraptorid dinosaurs (oofamily Elongatoolithidae), but have a distinctive type of ornamentation.

Continuoolithus nests, unlike those of Troodon and oviraptorids, would have been incubated under vegetation and sediment rather than brooding adults. Adaptations in the eggshell, such as high porosity and prominent ornamentation, would have helped the embryo breathe while buried. One fossil egg contains a tiny embryonic skeleton at an exceptionally young stage of development (perhaps eight to ten days old) showing the earliest stages of bone development.

Dictyoolithidae

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.

Egg fossil

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 era. 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.

Ellipsoolithus

Ellipsoolithus is an oogenus of dinosaur egg. It contains only a single oospecies, E. khedaensis. These eggs were laid by a theropod dinosaur.

Elongatoolithus

Elongatoolithus is an oogenus of Cretaceous small-to-medium sized theropod dinosaurs. The smallest species in this oogenus are E. excellens and the largest E. andrewsi and E. frustrabilis. The oogenus is smaller than Macroolithus. Fossils of this oogenus have been found in the fluvial, lacustrine and continental Pingling, Subashi, Jingangkou, Donggou, Yuanpu, and Daijiaping Formations of China, the Nemegt, Barun Goyot, and Djadokhta Formations of Mongolia and the El Castellar Formation of Spain.

Gigantoraptor

Gigantoraptor is a genus of giant oviraptorosaurian theropod dinosaur.

Guegoolithus

Guegoolithus is an oogenus of fossil egg from the Barremian of Spain. It is classified in the oofamily Spheroolithidae, and was probably laid by an ornithopod dinosaur.

Heishanoolithus

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 (1.2-1.3 mm thick), the dense covering of nodes on the eggshell surface, and for its relatively thin mammilary layer (making up only one eighth of the eggshell thickness). While no remains of Heishanoolithus have been associated with skeletal remains, strong evidence links Elongatoolithid eggs to Oviraptorosaurs.

Macroelongatoolithus

Macroelongatoolithus is an oogenus of large, fossil theropod eggs (probably representing a giant oviraptorid). They are known from Asia and from North America.

Macroolithus

Macroolithus is an oogenus (fossil-egg genus) 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.

Macroolithus eggs have been found containing oviraptorid dinosaur embryos resembling Heyuannia. Multiple other associations between oviraptorid and elongatoolithids (including other eggs containing embryos, parents brooding on nests, and a pair of shelled Macroolithus-like eggs preserved within an oviraptorid's pelvis) confirm that the parent of Macroolithus was an oviraptorid.

It is found in Upper Cretaceous formations of central and eastern Asia; fossils have been found in Mongolia, Kazakhstan and China. In the Nanxiong formation in Southern China, Macroolithus fossils range up to and possibly over the Cretaceous-Tertiary boundary, which is traditionally assumed to mark the extinction of the non-avian dinosaurs. Some paleontologists have interpreted the record of dinosaur eggs at this formation as supporting a gradual extinction event, rather than a sudden cataclysmic event. However, other paleontologists believe that these interpretations are merely based on artifacts of erosion and redeposition in the early Paleogene.

Nanshiungoolithus

Nanshiungoolithus is an oogenus of dinosaur egg.

Paraelongatoolithus

Paraelongatoolithus is a late Cretaceous oogenus of Chinese fossil egg, classified in the oofamily Elongatoolithidae, which represents the eggs of oviraptorosaurs.

Porituberoolithus

Porituberoolithus is an oogenus of dinosaur egg found in the late Campanian of Alberta. It was originally described as distinct from the Elongatoolithids on the basis of its ornamentation, but it was listed as a member of that oofamily by Wang et al. 2010. It is very similar to Subtiliolithus, but has a thicker shell.

Tacuarembovum

Tacuarembovum is an oogenus of fossil egg from the Cretaceous of Uruguay. It represents an Elongatoolithid, and pending future analysis may be found to be synonymous with another oospecies.

Trachoolithus

Trachoolithus is an oogenus of dinosaur egg.

Tubercuoolithus

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

Undulatoolithus

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.

Wayan Formation

The Wayan Formation is a geological formation in Idaho whose strata date back to the latest Early Cretaceous and the earliest Late Cretaceous. Dinosaur, other reptile, mammal, and micro and macro-floral remains are among the fossils that have been recovered from the formation. The lack of extensive outcrops, limited geographic extent, and extreme structural deformation have limited paleontological explorations of the Wayan.

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