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= Parvularugoglobigerina eugubina =

Parvularugoglobigerina eugubina was a species of planktonic foraminifera that lived during the Danian in the early Paleogene. It was one of the first species of planctonic foraminifera to evolve after the Cretaceous-Paleogene extinction event.

Description
The tests (shells) of Parvularugoglobigerina eugubina are trochospiral, meaning their chambers grew in a spiral pattern that rose slightly with each whirl. This results in the test having a raised spiral side, from which you can see all chambers, and a flat umbilical side, from which you can only see the chambers of the last whirl. A fully grown test constitutes 11-14 chambers distributed around 2 and a half whirls. Each subsequent chamber grew larger than the last, most noticably in the final whirl. The chamber walls have a microperforate texture and in cases of excellent preservation, pore-mounds can be seen on the surface of the test. The whole test is rather small, only being ca 0.1 mm wide. The aperture (opening through which the foram feeds) is mounted in an umbilical position on the final chamber, though the position can vary, with some individuals showing apertures on the spiral side or multiple apertures.

Stratigraphy
The first and last occurence of P. eugubina marks the base and top respectively of the Pα biostratigraphic zone of planktonic foraminifera, corresponding to the magnetochron C29r and an age of 64.97-64.8 Ma. This is the second biostratigraphic zone of the Paleocene, only preceded by the P0 zone. P. eugubina was discovered in the central Apennines (Italy) but has also been found in Alabama (USA), Shatsky rise (Northwestern Pacific), Alborz mountains (Iran) and El Kef (Tunisia).

Classification
The taxonomy of planktonic foraminifera lacks consensus, with multiple available phylogenies within foraminifera and unclear origins of the clade as a whole. One possible phylogenetic tree of how P. eugubina and its closest relatives radiated from Guembelitria cretacea immediately after the K-Pg boundary can be seen below. P. eugubina is thought to not have any living relatives as Parvularugoglobigerina alabamensis died out a few million years after P. eugubina in the Selandian. Later genetic studies support this fact by arguing that all cretaceous lineages of planktonic foraminifera died out in the K-Pg extinction or immediately after, and that Cenozoic lineages have their origins in benthic foraminifera that recolonized the planktonic niche.

Paleobiology
Like other planktonic foraminifera, P. eugubina would have lived in the open ocean and fed on other plankton by capturing them with with spines sticking out from the test. The nutrients of the prey are liberated by dissolving the prey with digestive enzymes, and then ingested through the aperture. Measurements of stable oxygen isotopes from DSDP site 384 suggest that P. eugubina lived in waters that were 14-15°C warm, likely deeper than the contempary species G. cretacea.