View source for Guegoolithus

{{Oobox
| fossil_range = {{fossil range|136|125|[[Early Cretaceous]]}}
| taxon = Guegoolithus
| authority = Moreno-Azanza ''et al.'', [[2014 in paleontology|2014]]
| subdivision_ranks = Oospecies
| subdivision = * {{extinct}}'''''G. turolensis''''' <small>Amo-Sanjuán ''et al.'', 2000 ([[Type species|type]])</small>
}}

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

==Distribution==
''Guegoolithus'' is known from the Early Cretaceous of Spain. It is common in the [[Maestrazgo]] Basin, dating to the lower [[Barremian]]. Fossils have been found in the [[Blesa Formation|Blesa]], [[El Castellar Formation|El Castellar]], [[Camarillas Formation|Camarillas]], and [[Mirambel Formation]]s.<ref name=MA2014/> It has also been found at the slightly older [[El Hocajo]], a part of the [[Cameros Basin]] which dates to the [[Valanginian]] or [[Hauterivian]] ages, up to 7 million years older than the Maestrazgo specimens.<ref name=MA2016/>

==Description==
''Guegoolithus'' is known from over 400 fossil eggshell fragments, but no complete eggs have been found. They are very thin for [[Spheroolithidae|spheroolithids]], ranging from 0.42 to 1.5&nbsp;mm in thickness.<ref name=MA2014>Moreno-Azanza, M., J.I. Canudo, and J.M. Gasca. (2014) "[https://www.researchgate.net/profile/Jose_Canudo/publication/263507846_Spheroolithid_eggshells_in_the_Lower_Cretaceous_of_Europe._Implications_for_eggshell_evolution_in_ornithischian_dinosaurs/links/54c7c8550cf238bb7d0b43a5.pdf Spheroolithid eggshells in the Lower Cretaceous of Europe. Implications for eggshell evolution in ornithischian dinosaurs.]" ''[[Cretaceous Research]]'' '''51''': 75–87.</ref> The wide range of eggshell thickness is partially due to erosion on the inner and outer surfaces of the fragments.<ref name="Amo Sanjuan et al 2000">Amo Sanjuan, O., Canudo, J.I., Cuenca-Bescos, G. (2000) "[https://www.researchgate.net/profile/Jose_Canudo/publication/263507846_Spheroolithid_eggshells_in_the_Lower_Cretaceous_of_Europe._Implications_for_eggshell_evolution_in_ornithischian_dinosaurs/links/54c7c8550cf238bb7d0b43a5.pdf 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.</ref> The size and shape of the complete egg is unknown.<ref name=MA2014/>

Like other types of dinosaur eggs, the shell of ''Guegoolithus'' is 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.<ref name=MA2016>{{cite journal |last1=Moreno-Azanza |first1=Miguel |last2=Gasca |first2=José Manuel |last3=Díaz-Martínez |first3=Ignacio |last4=Bauluz Lázaro |first4=Blanca |last5=Canudo Sanagustín |first5=José Ignacio |last6=Fernández |first6=Arturo |last7=Pérez-Lorente |first7=Félix |title=A multi-ootaxic assemblage from the Lower Cretaceous of the Cameros Basin (La Rioja; Northern Spain) |journal= Spanish Journal of Palaeontology|date=2016 |volume=31 |issue=2 |pages=305–320 |doi=10.7203/sjp.31.2.17158 |url=https://zaguan.unizar.es/record/58565/files/texto_completo.pdf|doi-access=free }}</ref> The surface of the eggshell exhibits sagenotuberculate ornamentation (nodes and ridges forming a net-like pattern, with pits and grooves in between<ref name="Carpenter">Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past). Indiana University Press, Bloomington, Indiana.
</ref>). It has a prolatocanaliculate pore system, similar to ''[[Spheroolithus]]'', which means that the pores are irregularly shaped and vary in width along their length. Also like ''Spheroolithus'', it has a prolatospherulitic morphotype, with eggshell units fused together and horizontal growth lines on the lower portion of the eggshell. ''Guegoolithus'' has much more prominent ornamentation that ''Spheroolithus'', and a thinner eggshell than most ''Spheroolithus'' species.<ref name=MA2014/>

==History==
''Guegoolithus'' was first discovered in [[2000 in paleontology|2000]] by Spanish paleontologists Olga Amo-Sanjuán, José Ignacio Canudo, and Gloria Cuenca-Bescós, though it was described as an oospecies of ''[[Macroolithus]]''. In [[2008 in paleontology|2008]], a paper suggested that ''"M." turolensis'' be used as an [[index fossil]] for fossil sites in the [[Sistema Ibérico]], because they are easily identifiable and always found in rocks of [[Hauterivian]]-[[Barremian]] age.<ref>M. Moreno-Azanza, J. M. Gasca, and J. I. Canudo. (2008) "[https://www.researchgate.net/profile/Jose_Canudo/publication/265820257_Macroolithus_turolensis_como_fsil_gua_para_el_Hauteriviense_superior-_Barremiense_basal_de_Teruel/links/54c27c080cf2911c7a48782e.pdf  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.</ref> An analysis in 2014 by Miguel Moreno-Azanza, José Ignacio Canudo, and José Manuel Gasca found that in fact, ''"M." turolensis'' is not an elongatoolithid, but instead belongs in Spheroolithidae, and named a new oogenus for it: ''Guegoolithus''.<ref name=MA2014/> In 2016, Moreno-Azanza and several of his colleagues reported the discovery of a new fossil site in [[La Rioja (Spain)|La Rioja]], [[Spain]], which included eggs assigned to ''Guegoolithus''. Since this site is somewhat older than the [[Barremian]] age of the previously reported ''Guegoolithus'' fossils, Moreno ''et al.'' rejected the idea of using them as index fossils.<ref name=MA2016/>

==Classification==
While it was previously considered an oospecies of ''Macroolithus'' in the oofamily Elongatoolithidae, ''Guegoolithus'' is 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 of ''[[Spheroolithus]]'' and Speroolithidae.<ref name=MA2014/>

==Paleobiology==
[[Image:Gideonmantellia.jpg|thumb|Life restoration of ''[[Gideonmantellia]]'', a candidate for a parent of ''Guegoolithus''.]]
''Guegoolithus'' is classified as a spheroolithid, which would indicate it was laid by an [[ornithopod]] [[dinosaur]]. It is very similar to the eggs of ''[[Maiasaura peeblesorum]]'' and other [[hadrosaurs]], but these were not common in [[Europe]] during the [[Early Cretaceous]]. ''G. turolensis'' is most likely laid by a closely related ornithopods.<ref name=MA2014/> [[Styracostern]]s (a clade of ornithopods that includes hadrosaurs and their close relatives) are, like ''G. turolensis'', incredibly common in the lower Cretaceous of Spain. Given that fossils of ''Guegoolithus'' span a larger time period than is likely for a single species, the fossils probably represent many different styracostern species with structurally indistinguishable eggshells. Because ''Guegoolithus'' remained unchanged for upwards of 5 million years and it is very similar to the late Cretaceous spheroolithids, Moreno-Azanza ''et 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 were [[altricial]].<ref name=MA2017>{{cite journal |last1=Moreno-Azanza |first1=Miguel |last2=Bauluz |first2=Blanca |last3=Ignacio Canudo |first3=José |last4=Mateus |first4=Octávio |title=The conservative structure of the ornithopod eggshell: electron backscatter diffraction characterization of ''Guegoolithus turolensis'' from the Early Cretaceous of Spain |journal=Journal of Iberian Geology |date=2017 |volume=43 |issue=2 |pages=235–243 |doi=10.1007/s41513-017-0019-1 |bibcode=2017JIbG...43..235M |s2cid=55380504 }}</ref>

Its reclassification outside of [[Elongatoolithidae]] implies that no elongatoolithids are known from the early Cretaceous of Europe. However, elongatoolithids have been reported from the [[Late Cretaceous]] of [[France]].<ref name=MA2014/>

==References==
{{Reflist}}

{{Taxonbar|from=Q22286403}}

{{Ornithopoda|E.}}

[[Category:Egg fossils]]
[[Category:Dinosaur reproduction]]
[[Category:Early Cretaceous dinosaurs of Europe]]
[[Category:Ornithopods]]
[[Category:Cretaceous Spain]]
[[Category:Fossils of Spain]]
[[Category:Camarillas Formation]]
[[Category:Fossil parataxa described in 2014]]