Cairanoolithus

Cairanoolithusis anoogenusofdinosaur eggwhich is found in Southwestern Europe. The eggs are large (15–19 centimetres or 6–7+1⁄2inches in diameter) and spherical. Their outer surface is either smooth, or covered with a subdued pattern of ridges interspersed with pits and grooves. Multiple fossilegg clutchesare known but the nest structure is unclear.
The parent ofCairanoolithusis probably some kind of non-ornithopodornithischian, possibly thenodosauridStruthiosaurus.
The eggs were first named in 1994, when the two oospecies were classified in distinct oogenera asCairanoolithus dughiiandDughioolithus roussetensis. They are now considered to belong in a single oogenus, possibly even a single oospecies. Though it has been classified as amegaloolithid,Cairanoolithusis now placed in its own oofamily, Cairanoolithidae.
Cairanoolithuseggs are spherical and fairly large, measuring15–19 cm (6–7+1⁄2in) in diameter.The outer surface is smooth or covered with a subdued netlike pattern of ridges, interspersed with pits and grooves (sagenotuberculate ornamentation).The eggshells are made up of partially interlocking column-shaped shell units and range from1.10 to 2.65 mm (3⁄64to13⁄128in) thick.
Several egg clutches ofC. dughiiare known, containing as many as 25 fossilized eggs.Unfortunately,taphonomicalalterations (changes during the fossilization process) make it difficult to determine the original structure of the nest. Cousin (2002) hypothesized thatCairanoolithuseggs were laid on the surface of the ground, possibly buried beneath a mound of plant matter.Tanakaet al.(2015) noted that the shell had a high rate of water vapor conductance. Therefore, they concluded thatCairanoolithusnests were covered by organic or inorganic material, similar to modern eggs with high vapor conductance.
Two oospecies ofCairanoolithushave been described:
Some authors consider the two oospecies to be synonymous. Cousin (2002) argued that the differences between them were due tointraspecificvariation or due to taphonomy. He also described several eggshell fragments that possibly belong to an additional distinct oospecies ofCairanoolithus;however these specimens were referred toC. roussetensisby Selles and Galobart (2015).
While it was formerly considered amegaloolithid,Cairanoolithusis now considered to belong its ownmonotypicoofamily, Cairanoolithidae. It belongs to the dinosauroid-spherulitic basic type, a group includingsauropodeggs andornithischianeggs, butparaphyleticallyexcludingtheropodeggs.
Thecladistic analysisdone by Selles and Galobart in 2015 recoveredCairanoolithusas a sister taxon to the clade ofornithopodeggsGuegoolithus,Spheroolithus, andOvaloolithus. Therefore, they considered it likely thatCairanoolithusbelongs to a non-ornithopod ornithischian dinosaur.
Since embryos are unknown in cairanoolithid eggs, the identity of their parent is uncertain. They have long been considered to be eggs oftitanosaursor ornithopods (likeRhabdodon).However, numerous characteristics distinguishCairanoolithusfrom sauropod eggs (oofamilies Megaloolithidae andFaveoloolithidae), even though they bear superficial similarities in size and shape.Cairanoolithus's columnar eggshell units are quite unlike the fan-shaped ones seen inMegaloolithus,Faveoloolithus, orFusioolithus. Also, its subdued ornamentation contrasts strongly with the heavily sculpted eggshells of sauropod eggs, and it has a different pore system.Eggs of ornithopods (SpheroolithidaeandOvaloolithidae), 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.
The cladistic analysis by Sellés and Galobart in 2015 supported an ornithischian parentage. LateCampanianto earlyMaastrichtianornithischians from Southwestern Europe are restricted torhabdodontidsand thenodosauridStruthiosaurus. When Sellés and Galobart analyzed the pelvises ofRhabdodon(the largest known rhabdodontid) andStruthiosaurus, they found thatRhabdodoncould not have laid eggs as big asCairanoolithus.On the other hand, even thoughStruthiosauruswas relatively small, the unique orientation of its ischia would have easily allowed it to lay eggs as large as a19 cm (7+1⁄2in) cairanoolithid egg.However, interpretingCairanoolithusas the eggs of a nodosaur does raise the question of whyCairanoolithusor similar eggs have not been found in areas with a greater nodosaur abundance.
Cairanoolithusis native to Southwestern Europe, including southernFranceand northernIberia. Its fossils date to the lateCampanianto earlyMaastrichtian.They are usually found in theAix-en-ProvenceBasin below theRognac Limestone.C. dughiiis from the La Cairanne site inBouches du Rhône, France, fromRoquehautes-Grand Creuxand from theVilleveyrac Basin.C. roussetensisis found in the northern part of Iberia (Tremp Groupof Spain),and from southern France (inRousset Village,Roquehautes-Crete du Marbre, the Villeveyrac Basin, andArgelliers-Montamaud).
The Late Cretaceous ecosystems of Europe (which was then an island archipelago) show complex mixing of taxa originating from Africa, Asia, and North America.In Southwestern Europe,Cairanoolithusco-occurs with numerous other types of fossil eggs;Megaloolithusis particularly common,but theropod eggs such asPrismatoolithusand the ornithopod eggGuegoolithusare also present. Dinosaur body fossils are also common, including nodosaurids, rhabdodontids, titanosaurs,dromaeosaurids, basaliguanodontians,hadrosaurids,neoceratosaurians, andcoelurosaurs. Other vertebrates includebony fish,squamates,cryptodiranturtles,alligatorids, andmammals.
The Aix Basin was first excavated for fossils in 1869 by French paleontologistPhilippe Matheron.In the 1950s, Raymond Dughi and Francois Sirugue, a pair of French paleontologists working for theMuseum d'Histoire Naturelle Aix-en-Provence, extensively studied the basin's fossil eggshells.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 paleontologistP. Kerourio and the German paleontologistH. K. Erben.
In his 1983 doctoral thesis, M. M. Penner devised one of the early classification schemes for egg fossils.He was the first to recognize the eggs now namedCairanoolithusas a distinct type; under his classification scheme, they were called "Group 2".In 1994, French paleontologists M. Vianey-Liaud, P. Mallan, O. Buscail and C. Montgelard described them under the modern parataxonomic system asCairanoolithus dughiiand"Dughioolithus" roussetensis.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.Following further discoveries in 2001, Géraldine Garcia and Monique Vianey-Liaudsynomizedthe two oogenera.In 2002, French paleontologist R. Cousin took a step further and synonymized the two oospecies.
In 2012, the firstCairanoolithusfossils discovered outside of France were first reported byAlbert G. Sellesin hisPhD thesisatUniversitat de Barcelona, in which he also proposed thatCairanoolithusbe moved into its own oofamily.Three years later, Selles andAngel Galobartpublished a comprehensive reanalysis ofCairanoolithus, in which they formally named the new oofamily, Cairanoolithidae, to containCairanaoolithus. Contrary to Cousin's conclusions, Selles and Galobart separated the oospeciesC. dughiiandC. roussetensis. Also, they demonstrated thatCairanoolithuswas not the eggs of an ornithopod or sauropod and conjectured that it could be the eggs of a nodosaur.