Guegoolithusis anoogenusoffossil eggfrom theearly Cretaceousof Spain. It is classified in the oofamilySpheroolithidae,and was probably laid by anornithopoddinosaur.
| Guegoolithus Temporal range:
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|---|---|
Egg fossil classification
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| Basic shell type: | †Dinosauroid-spherulitic |
| Oofamily: | †Spheroolithidae |
| Oogenus: | †Guegoolithus Moreno-Azanzaet al.,2014 |
| Oospecies | |
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Distribution
editGuegoolithusis known from the Early Cretaceous of Spain. It is common in theMaestrazgoBasin, dating to the lowerBarremian.Fossils have been found in theBlesa,El Castellar,Camarillas,andMirambel Formations.[1]It has also been found at the slightly olderEl Hocajo,a part of theCameros Basinwhich dates to theValanginianorHauterivianages, up to 7 million years older than the Maestrazgo specimens.[2]
Description
editGuegoolithusis known from over 400 fossil eggshell fragments, but no complete eggs have been found. They are very thin forspheroolithids,ranging from 0.42 to 1.5 mm in thickness.[1]The wide range of eggshell thickness is partially due to erosion on the inner and outer surfaces of the fragments.[3]The size and shape of the complete egg is unknown.[1]
Like other types of dinosaur eggs, the shell ofGuegoolithusis made up of tightly packed crystalline units. The shell is single-layered, but the shell units appear to have two distinct layers because they exhibit a radiating acicular crystal structure near the base (the inner edge of the eggshell), but form a tabular ultrastructure on the upper third of the eggshell.[2]The surface of the eggshell exhibits sagenotuberculate ornamentation (nodes and ridges forming a net-like pattern, with pits and grooves in between[4]). It has a prolatocanaliculate pore system, similar toSpheroolithus,which means that the pores are irregularly shaped and vary in width along their length. Also likeSpheroolithus,it has a prolatospherulitic morphotype, with eggshell units fused together and horizontal growth lines on the lower portion of the eggshell.Guegoolithushas much more prominent ornamentation thatSpheroolithus,and a thinner eggshell than mostSpheroolithusspecies.[1]
History
editGuegoolithuswas first discovered in2000by Spanish paleontologists Olga Amo-Sanjuán, José Ignacio Canudo, and Gloria Cuenca-Bescós, though it was described as an oospecies ofMacroolithus.In2008,a paper suggested that"M." turolensisbe used as anindex fossilfor fossil sites in theSistema Ibérico,because they are easily identifiable and always found in rocks ofHauterivian-Barremianage.[5]An analysis in 2014 by Miguel Moreno-Azanza, José Ignacio Canudo, and José Manuel Gasca found that in fact,"M." turolensisis not an elongatoolithid, but instead belongs in Spheroolithidae, and named a new oogenus for it:Guegoolithus.[1]In 2016, Moreno-Azanza and several of his colleagues reported the discovery of a new fossil site inLa Rioja,Spain,which included eggs assigned toGuegoolithus.Since this site is somewhat older than theBarremianage of the previously reportedGuegoolithusfossils, Morenoet al.rejected the idea of using them as index fossils.[2]
Classification
editWhile it was previously considered an oospecies ofMacroolithusin the oofamily Elongatoolithidae,Guegoolithusis now considered a spheroolithid because of the similarities of microstructure, ultrastructure, and ornamentation. It contains a single oospecies:G. turolensis.Unfortunately, relationships within Spheroolithidae are not well known because of the unclear definitions ofSpheroolithusand Speroolithidae.[1]
Paleobiology
edit
Guegoolithusis classified as a spheroolithid, which would indicate it was laid by anornithopoddinosaur.It is very similar to the eggs ofMaiasaura peeblesorumand otherhadrosaurs,but these were not common inEuropeduring theEarly Cretaceous.G. turolensisis most likely laid by a closely related ornithopods.[1]Styracosterns(a clade of ornithopods that includes hadrosaurs and their close relatives) are, likeG. turolensis,incredibly common in the lower Cretaceous of Spain. Given that fossils ofGuegoolithusspan a larger time period than is likely for a single species, the fossils probably represent many different styracostern species with structurally indistinguishable eggshells. BecauseGuegoolithusremained unchanged for upwards of 5 million years and it is very similar to the late Cretaceous spheroolithids, Moreno-Azanzaet al.(2017) concluded that the nesting behavior of hadrosaurs and their close relatives remained unchanged for 80 million years. The eggshell structure is apparently designed to be easily broken from the inside, indicating that these dinosaurs werealtricial.[6]
Its reclassification outside ofElongatoolithidaeimplies that no elongatoolithids are known from the early Cretaceous of Europe. However, elongatoolithids have been reported from theLate CretaceousofFrance.[1]
References
edit- ^abcdefghMoreno-Azanza, M., J.I. Canudo, and J.M. Gasca. (2014) "Spheroolithid eggshells in the Lower Cretaceous of Europe. Implications for eggshell evolution in ornithischian dinosaurs."Cretaceous Research51:75–87.
- ^abcMoreno-Azanza, Miguel; Gasca, José Manuel; Díaz-Martínez, Ignacio; Bauluz Lázaro, Blanca; Canudo Sanagustín, José Ignacio; Fernández, Arturo; Pérez-Lorente, Félix (2016)."A multi-ootaxic assemblage from the Lower Cretaceous of the Cameros Basin (La Rioja; Northern Spain)"(PDF).Spanish Journal of Palaeontology.31(2): 305–320.doi:10.7203/sjp.31.2.17158.
- ^Amo Sanjuan, O., Canudo, J.I., Cuenca-Bescos, G. (2000) "First record of elongatoolithid eggshells from the Lower Barremian (Lower Cretaceous) of Europe (Cuesta Corrales 2, Galve Basin, Teruel, Spain)."In: Bravo, A.M., Reyes, T. (Eds.),First International symposium on Dinosaur eggs and babies. Extended abstracts. Isona i Conca Della,pp. 7–14.
- ^Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past). Indiana University Press, Bloomington, Indiana.
- ^M. Moreno-Azanza, J. M. Gasca, and J. I. Canudo. (2008) "Macroolithus turolensis como fósil guia para el Hauteriviense superior-Barremiense basal de Teruel"In J I Ruiz-Omeñaca, L Piñuela and J C García-Ramos (eds),XXIV Jornadas de la Sociedad Española de Paleontología,15–18 October 2008, Museo del Jurásico de Asturias (MUJA), Colunga, Spain, Libro de Resúmenes 43–44.
- ^Moreno-Azanza, Miguel; Bauluz, Blanca; Ignacio Canudo, José; Mateus, Octávio (2017). "The conservative structure of the ornithopod eggshell: electron backscatter diffraction characterization ofGuegoolithus turolensisfrom the Early Cretaceous of Spain ".Journal of Iberian Geology.43(2): 235–243.Bibcode:2017JIbG...43..235M.doi:10.1007/s41513-017-0019-1.S2CID55380504.