View source for Earth:Styloolithus

{{short description|Oogenus of fossil egg}}
{{Oobox
| fossil_range = {{fossil range|100|66|[[Earth:Upper Cretaceous|Upper Cretaceous]]}}
| image = Styloolithus.jpg
| image_caption = Two partial cluthces
| taxon = Styloolithus
| authority = 
| subdivision_ranks = Oospecies
| subdivision = 
* {{extinct}}'''''S. sabathi'''''
}}

'''''Styloolithus''''' is an oogenus of highly distinctive fossil egg from the [[Earth:Upper Cretaceous|Upper Cretaceous]] Djadokhta Formation and the [[Earth:Barun Goyot Formation|Barun Goyot Formation]] in Mongolia.<ref name="Varracchio and Barta 2015">Varricchio, D.J. and D.E. Barta (2015). "[https://www.app.pan.pl/article/item/app000852014.html Revisiting Sabath's "Larger Avian Eggs" from the Gobi Cretaceous]" ''Acta Palaeontologica Polonica'' 60(1):11-25.</ref>

==History==
The eggs of ''Styloolithus'' were first discovered in 1991 by Karol Sabath in an assemblage of fossil eggs in the Gobi desert, and were described as "larger avian eggs".<ref name="Sabath 1991">Sabath, K. (1991). "[https://www.app.pan.pl/archive/published/app36/app36-151.pdf Upper Cretaceous amniotic eggs from the Gobi Desert]". ''Acta Palaeontologica Polonica'' 36: 151–192.</ref> They were considered classified as ''[[Earth:Gobioolithus|Gobioolithus major]]'' in 1996 by Mikhailov.<ref name="Varracchio and Barta 2015"/> In 2015, Varracchio and Barta redefined ''G. major'', and reclassified the "larger avian eggs" into an entirely new oogenus, ''Styloolithus''.

==Description==
[[File:Styloolithus and Gobioolithus.jpg|thumb|left|''Styloolithus'' egg next to two ''Gobioolithus'']] 
The [[Biology:Type|type specimen]] of ''Styloolithus'' is a fossil [[Biology:Clutch (eggs)|clutch]] of at least four eggs and associated adult remains (probably representing the parent). Several other fossil eggs are also known. The egg clutches are tightly packed together, like ''[[Earth:Prismatoolithus|Prismatoolithus]]'' and Troodontid eggs, in contrast to the loosely scattered nests of enantiornithine birds. However, the eggs themselves are quite different from Troodontids, and the associated skeletal remains are similar to the enantiornithine ''Gobipteryx minuta'' (=''Nanantius valifanovi'').<ref name="Varracchio and Barta 2015"/>

''S. sabathi'' eggs are quite different from all other known fossil eggs of the [[Earth:Cretaceous|Cretaceous]]. At 70 mm long and 32 mm across, they are larger than both oospecies of ''[[Earth:Gobioolithus|Gobioolithus]]'', and more elongated. It can be distinguished from all non-avian [[Biology:Dinosaur|dinosaur]] eggs by the thick third layer of the shell (possibly representing an external zone). It lacks shell ornamentation, unlike ''Elongatoolithus'' and ''[[Biology:Macroelongatoolithus|Macroelongatoolithus]]''.<ref name="Varracchio and Barta 2015"/>

The eggs are interesting because of the possible presence of an external zone, the outer layer of the eggshell which is rare outside of bird eggs.<ref name="UCMP"> Laura E. Wilson, Karen Chin, Frankie D. Jackson, and Emily S. Bray. [http://www.ucmp.berkeley.edu/science/eggshell/eggshell2.php II. Eggshell morphology and structure]. ''UCMP Online Exhibits: Fossil Eggshell'' </ref> If correctly interpreted, this would prove that ''Styloolithus'' in fact represents bird eggs. However, it cannot be proven to have an external layer until its shell is examined by scanning electron microscopy.<ref name="Varracchio and Barta 2015"/>

==Parataxonomy==
When they were first discovered in 1991, ''Styloolithus'' eggs (then unnamed) were described as bird eggs.<ref name="Sabath 1991"/> The three phylogenetic analyses performed by Varracchio and Barta (2015) were inconclusive as to whether it represented a bird or a non-avian theropod. However, it is most likely avian because it has an unornamented, thin shell that probably has three structural layers, a combination of characters unique to bird eggs.<ref name="Varracchio and Barta 2015"/> Also, the bones found associated with the eggs seem to be avian.<ref name="Varracchio and Barta 2015"/><ref name="Sabath 1991"/>

==Palaeobiology==
The association of adult bones with ''Styloolithus'' eggs suggests intense parental care.<ref name="Sabath 1991"/> The tight egg clutches show that the incubation methods differed from that of ''Gobipteryx''. Like Troodontids, the parents of ''Styloolithus'' probably sat on top of largely buried eggs. It is unknown whether ''S. sabathi'' was incubated by the father or the mother of the eggs.<ref name="Varracchio and Barta 2015"/>

==References==
{{Reflist}}

{{Taxonbar|from=Q22285929}}

[[Category:Campanian life]]
[[Category:Barun Goyot Formation]]

{{Sourceattribution|Styloolithus}}