Cairanoolithus

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Cairanoolithus
Temporal range: Late Cretaceous
Cairanoolithus dughii
Egg fossil classification Edit this classification
Basic shell type: †Dinosauroid-spherulitic
Oofamily: †Cairanoolithidae
Sellés and Galobart, 2015
Oogenus: †Cairanoolithus
Vianey-Liaud et al., 1994
Oospecies
  • C. dughii (type) Vianey-Liaud et al., 1994
  • C. roussetensis Vianey-Liaud et al., 1994
Synonyms
  • Dughioolithus Vianey-Liaud et al., 1994

Cairanoolithus is an

egg clutches
are known but the nest structure is unclear.

The parent of Cairanoolithus is probably some kind of non-

nodosaurid Struthiosaurus
.

The eggs were first named in 1994, when the two oospecies were classified in distinct oogenera as Cairanoolithus dughii and Dughioolithus roussetensis. They are now considered to belong in a single oogenus, possibly even a single oospecies. Though it has been classified as a

megaloolithid, Cairanoolithus is now placed in its own oofamily, Cairanoolithidae.[1][2]

Description

Size of the smallest and largest eggs attributed to Cairanoolithus

Cairanoolithus eggs are spherical and fairly large, measuring 15–19 cm (6–7+1⁄2 in) in diameter.[2][3] The outer surface is smooth or covered with a subdued netlike pattern of ridges, interspersed with pits and grooves (sagenotuberculate ornamentation).[1][2] The eggshells are made up of partially interlocking column-shaped shell units and range from 1.10 to 2.65 mm (3⁄64 to 13⁄128 in) thick.[2]

Several egg clutches of C. dughii are known, containing as many as 25 fossilized eggs.[2] Unfortunately, taphonomical alterations (changes during the fossilization process) make it difficult to determine the original structure of the nest. Cousin (2002) hypothesized that Cairanoolithus eggs were laid on the surface of the ground, possibly buried beneath a mound of plant matter.[4] Tanaka et al. (2015) noted that the shell had a high rate of water vapor conductance. Therefore, they concluded that Cairanoolithus nests were covered by organic or inorganic material, similar to modern eggs with high vapor conductance.[5]

Oospecies

Two oospecies of Cairanoolithus have been described:

  • Cairanoolithus dughii is the type oospecies. At 1.57–2.41 mm (1⁄16–3⁄32 in), its eggshell is slightly thicker than that of C. roussetensis. It has slender, partially fused columnar eggshell units. Their outer surface is almost without ornamentation, and the inner surface is covered with hollows once filled by organic cores. C. dughii's eggshell exhibits an angusticanaliculate pore system, i.e. its pores are long, narrow, and straight.[1][2]
  • Cairanoolithus roussetensis, which was formerly classified in its own oogenus, Dughioolithus, can be distinguished from C. dughii by its thinner eggshell (measuring 1.11–1.77 mm or 3⁄64–9⁄128 in thick), its broader eggshell units, and the relative prominence of its ornamentation.[2] Like C. dughii, C. roussetensis typically has an angusticanaliculate pore system, though some specimens have prolatocanaliculate pores, meaning they have variable diameter across their length.[1][2]

Some authors consider the two oospecies to be synonymous. Cousin (2002) argued that the differences between them were due to

intraspecific variation or due to taphonomy. He also described several eggshell fragments that possibly belong to an additional distinct oospecies of Cairanoolithus;[4] however these specimens were referred to C. roussetensis by Selles and Galobart (2015).[2]

Classification

See also:
Egg fossils § Classification
 
Archosauria
 

Theropoda

Crocodylomorpha

"non‑theropod dinosaurs"

Prosauropod
egg

Megaloolithus jabalpurensis

M. dhoridungriensis

Faveoloolithus

Simplified version of Selles and Galobart's cladogram, showing the position of Cairanoolithus relative to other non-theropod dinosaur eggs.

While it was formerly considered a

theropod eggs.[2]

The

ornithopod eggs Guegoolithus, Spheroolithus, and Ovaloolithus. Therefore, they considered it likely that Cairanoolithus belongs to a non-ornithopod ornithischian dinosaur.[2]

Parentage

Since embryos are unknown in cairanoolithid eggs, the identity of their parent is uncertain. They have long been considered to be eggs of

Ovaloolithidae), on the other hand, show much closer similarity to cairanoolithids in ornamentation and pore system. However, ornithopod eggs are typically much smaller, and the crystal structure of their eggshell units is distinct.[2]

Restorations of Struthiosaurus, the possible parent of Cairanoolithus

The cladistic analysis by Sellés and Galobart in 2015 supported an ornithischian parentage. Late

nodosaurid Struthiosaurus. When Sellés and Galobart analyzed the pelvises of Rhabdodon (the largest known rhabdodontid) and Struthiosaurus, they found that Rhabdodon could not have laid eggs as big as Cairanoolithus.[2] On the other hand, even though Struthiosaurus was relatively small, the unique orientation of its ischia would have easily allowed it to lay eggs as large as a 19 cm (7+1⁄2 in) cairanoolithid egg.[2] However, interpreting Cairanoolithus as the eggs of a nodosaur does raise the question of why Cairanoolithus or similar eggs have not been found in areas with a greater nodosaur abundance.[2]

Distribution

Cairanoolithus is native to Southwestern Europe, including southern

Tremp Group of Spain),[8] and from southern France (in Rousset Village, Roquehautes-Crete du Marbre, the Villeveyrac Basin, and Argelliers-Montamaud).[3][9]

Paleoecology

The Late Cretaceous ecosystems of Europe (which was then an island archipelago) show complex mixing of taxa originating from Africa, Asia, and North America.

alligatorids, and mammals.[10]

History

The Aix Basin was first excavated for fossils in 1869 by French paleontologist Philippe Matheron.[12] In the 1950s, Raymond Dughi and Francois Sirugue, a pair of French paleontologists working for the Museum d'Histoire Naturelle Aix-en-Provence, extensively studied the basin's fossil eggshells.[13] They divided the eggs they had found into ten different types, but they did not describe them in detail. In the 1970s and 1980s, further work was done by the French paleontologist[14] P. Kerourio and the German paleontologist[15] H. K. Erben.[3]

In his 1983 doctoral thesis, M. M. Penner devised one of the early classification schemes for egg fossils.[2][16] He was the first to recognize the eggs now named Cairanoolithus as a distinct type; under his classification scheme, they were called "Group 2".[2] In 1994, French paleontologists M. Vianey-Liaud, P. Mallan, O. Buscail and C. Montgelard described them under the modern parataxonomic system as Cairanoolithus dughii and "Dughioolithus" roussetensis.[3] They did not assign either of them to any oofamily, but both oogenera were classified in the oofamily Megaloolithidae by the Russian paleontologist Konstantin Mikhailov in 1996.[6] Following further discoveries in 2001, Géraldine Garcia and Monique Vianey-Liaud synomized the two oogenera.[17] In 2002, French paleontologist R. Cousin took a step further and synonymized the two oospecies.[4]

In 2012, the first Cairanoolithus fossils discovered outside of France were first reported by

Universitat de Barcelona, in which he also proposed that Cairanoolithus be moved into its own oofamily.[18] Three years later, Selles and Angel Galobart published a comprehensive reanalysis of Cairanoolithus, in which they formally named the new oofamily, Cairanoolithidae, to contain Cairanaoolithus. Contrary to Cousin's conclusions, Selles and Galobart separated the oospecies C. dughii and C. roussetensis. Also, they demonstrated that Cairanoolithus was not the eggs of an ornithopod or sauropod and conjectured that it could be the eggs of a nodosaur.[2]

References

  1. ^
    ISBN 978-0253334978
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  2. ^
    S2CID 85205835
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  3. ^ a b c d e f g M. Vianey-Liaud, P. Mallan, O. Buscail and C. Montgelard. (1994) "Review of French dinosaur eggshells: morphology, structure, mineral, and organic composition." Dinosaur Eggs and Babies, Cambridge University Press, Cambridge. pp 151-183
  4. ^ a b c Cousin, R. (2002). "Organisation des postes de dinosauriens de la paralamille des Megaloolithidae Zhao, 1979 [Organization of the dinosaur nest of the parafamily Megaloolithidae Zhao 1979]". Bulletin Trimestriel de la Société Géologique de Normadie et des Amis du Muséus du Havre (in French). 89: 1–177.
  5. PMID 26605799
    .
  6. ^
    JSTOR 4523773
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  7. S2CID 86208659
    .
  8. ^ Sellés, A. G.; Vila, B. (2015). "Re-evaluation of the age of some dinosaur localities from the southern Pyrenees by means of megaloolithid oospecies". Journal of Iberian Geology. 41: 125–139.
  9. doi:10.1016/j.cretres.2012.05.004
    .
  10. ^
    S2CID 82961064
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  11. doi:10.1016/j.cretres.2014.05.017
    .
  12. ^ Matheron, P. (1869). "Notice sur les reptiles fossiles des dépôts fluvio-lacustres crétacés du bassin à lignite de Fuveau". Mémoires de l'Académie Impériale des Sciences. Belles-Lettres et Arts de Marseille (in French): 345–379.
  13. ISBN 9780521779302
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  14. doi:10.1016/s0016-6995(81)80126-x
    .
  15. ^ Wilford, John Noble (November 9, 1986). "New data extend era of dinosaurs". New York Times. Retrieved 22 May 2016.
  16. ^ Carpenter, K.; Hirsch, K.F.; Horner, J.R. (1994). "Introduction". Dinosaur Eggs and Babies. Cambridge: Cambridge University Press. pp. 1–11.
  17. doi:10.1016/S1251-8050(00)91401-0
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  18. hdl:2445/35482
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