Sankofais anoogenusofprismatoolithidegg. They are fairly small, smooth-shelled, and asymmetrical.Sankofamay represent the fossilized eggs of atransitional speciesbetween non-aviantheropodsandbirds.[1]
| Sankofa Temporal range:
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|---|---|
Egg fossil classification
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| Basic shell type: | †Dinosauroid-prismatic |
| Oofamily: | †Prismatoolithidae |
| Oogenus: | †Sankofa López-Martínez & Vicens, 2012 |
| Oospecies | |
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Etymology
editThe nameSankofacomes from theAshanteword "sankofa",meaning 'learning from the past', symbolized by a bird with an egg in its bill. The oospecific epithetpyrenaicarefers to thePyrenees,where the eggs were first discovered.[1]
Distribution
editSankofa pyrenaicais known solely from theAren Formation,in the southernPyreneesofCatalonia,Spain, dating from the UpperCampanianto LowerMaastrichtian.[1]
Description
editSankofaeggs are uniformly 7 cm long and 4 cm wide, and their eggshell averages 0.27 mm thick. The eggshell consists of two layers, the prismatic (or palisade) layer and the mammillary layer, similar to most other non-avian dinosaur eggshells.[2]InSankofa,these two layers have a gradual boundary, and the mammillary layer is much thinner than the prismatic. The prismatic has a slightly squamatic microstructure, very similar to the eggs ofTroodonand otherprismatoolithids,a step towards the fully squamatic texture of bird eggs. The eggshell has a smooth surface with no trace of ornamentation, and highly variable pore density.[1]
The most significant characteristic ofSankofais its shape: they are asymmetric, with an ovoid shape, like bird eggs. A morphometric analysis byLópez-Martínezand Vicens in 2012 found that it was an intermediate shape between avian and non-avian theropods, and also very similar to anenantiornithineegg from theBajo de la Carpa FormationinArgentina,though their microstructures are quite different.[1]
Classification
editParataxonomically,Sankofais classified in the oofamily Prismatoolithidae, because of its microstructure.Cladistic analysisfoundSankofato be in apolytomywithProtoceratopsidovum,Troodoneggs, and birds. The mosaic of avian and non-avian characteristics makes it uncertain whetherS. pyrenaicawas laid by a bird or a non-avian theropod, and provides further evidence for the theory thatbirds evolved from dinosaurs.[1]It probably represents a transitional form between the two groups.[1]
References
edit- ^abcdefgLópez-Martínez, Nieves; Vicens, Enric (2012-03-01)."A new peculiar dinosaur egg, Sankofa pyrenaica oogen. nov. oosp. nov. from the Upper Cretaceous coastal deposits of the Aren Formation, south-central Pyrenees, Lleida, Catalonia, Spain".Palaeontology.55(2): 325–339.doi:10.1111/j.1475-4983.2011.01114.x.ISSN1475-4983.
- ^Laura E. Wilson, Karen Chin, Frankie D. Jackson, and Emily S. Bray. (2012). "Fossil eggshell: Fragments from the past"UCMP's online fossil egg exhibit.