''Sankofa'' is an oogenus of prismatoolithid egg. They are fairly small, smooth-shelled, and asymmetrical. ''Sankofa'' may represent the fossilized eggs of a

transitional species A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross a ...

between non-avian theropods and

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

Etymology

The name ''Sankofa'' comes from the Ashante word "

sankofa (pronounced ''SAHN''-koh-fah) is a word in the Twi language of Ghana meaning “to retrieve" (literally "go back and get"; - to return; - to go; - to fetch, to seek and take) and also refers to the Bono Adinkra symbol represented either w ...

", meaning 'learning from the past', symbolized by a bird with an egg in its bill. The oospecific epiphet ''pyrenaica'' refers to the

Pyrenees The Pyrenees (; es, Pirineos ; french: Pyrénées ; ca, Pirineu ; eu, Pirinioak ; oc, Pirenèus ; an, Pirineus) is a mountain range straddling the border of France and Spain. It extends nearly from its union with the Cantabrian Mountains to C ...

, where the eggs were first discovered.

Distribution

''Sankofa pyrenaica'' is known solely from the Aren Formation, in the southern

Catalonia Catalonia (; ca, Catalunya ; Aranese Occitan: ''Catalonha'' ; es, Cataluña ) is an autonomous community of Spain, designated as a ''nationality'' by its Statute of Autonomy. Most of the territory (except the Val d'Aran) lies on the north ...

, Spain, dating from the Upper Campanian to Lower

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

Description

''Sankofa'' eggs 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.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. In ''Sankofa'', 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 of '' Troodon'' and other prismatoolithids, 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. The most significant characteristic of ''Sankofa'' is its shape: they are asymmetric, with an ovoid shape, like bird eggs. A morphometric analysis by López-Martínez and Vicens in 2012 found that it was an intermediate shape between avian and non-avian theropods, and also very similar to an

enantiornithine The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...

egg from the Bajo de la Carpa Formation in

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

, though their microstructures are quite different.

Classification

Parataxonomically, ''Sankofa'' is classified in the oofamily Prismatoolithidae, because of its microstructure. Cladistic analysis found ''Sankofa'' to be in a polytomy with ''

Protoceratopsidovum ''Protoceratopsidovum'' is an oogenus of dinosaur egg from Mongolia. Despite its name (which means "eggs of ''Protoceratops''"Zelenitsky, D., and Currie, P. (2004) "A Cladistic Analysis of Theropod Ootaxa." ''Journal of Vertebrate Paleontology.'' ...

'', ''Troodon'' eggs, and birds. The mosaic of avian and non-avian characteristics makes it uncertain whether ''S. pyrenaica'' was laid by a bird or a non-avian theropod, and provides further evidence for the theory that birds evolved from dinosaurs. It probably represents a transitional form between the two groups.

References

{{Taxonbar, from=Q16930745 Fossils of Spain Egg fossils Dinosaur reproduction Fossil parataxa described in 2012