Citation: Globigerina praeglobotruncanaeformis Bykova 1960Rank: speciesType specimens: pl. 3. fig. 3a-c, X 102: pl. 6, figs. 27, 28. Type age (chronostrat): Upper Middle Eocene or basal Upper Eocene. Type locality: Not designated. One figured specimen (fig. 3a-c) from the depth interval 352-360 m. in Ustyurt reference borehole no. 1, Ust-Urt Plateau, Central Asia. Type repository: Depository not given.
Original Description [Translation from the Russian. - A second stage in the "direct" line of development of the phylogenetic cycle /the first being the sltifting of the later chambers to the ventral side and the production of more evolute forms/ expresses itself in an increase in the size of the apertures and the umbilical area, owing to which a secondary flattening of the tests takes place. From Globigerina varianta Subbotina there arises G. inaequispira Subbotina. Forms appear within G. pseudoeocaena Subbotina with a large aperture. G. pseudoeocaena and G. eocaenica Terquem yield the species of the G. frontosa Subbotina group, which have a broad aperture. (The Globorotalia praenartaensis-Truncorotalia aragonensis var. caucasica group, studied by E. K. Shutskaya (1956, Akad. Nauk SSSR, lnst. Geol. Nauk, vypusk 164, geol. ser., no. 71, pp. 3-119), develops in a similar direction.) At the end of this stage a reverse tendency or a third stage of the cycle is noted - toward uncoiling (toward a reduction in evoluteness and trochiformity, leading also to a flattening of the test), a reduction in the size of the apertures and in the test size, and toward smoother walls (reduction in the diameter of foramina). These tendencies are clearly revealed in the reference section of Severo-Ustyurt borehole 1. Here (at a depth of 237-392 m.) in deposits corresponding to the upper part of the Middle Eocene (Acarinina crassaformis Zone), and apparently to the base of the Upper Eocene, together with Globigerina inaequispira, G. varianta, G. pseudoeocaena, etc., which are usual for the Middle Eocene, there appear unusual four- and five-chambered globigerinid forms (Globigerina praeglobotruncanaeformis Bykova, n. sp.), which show a tendency toward uncoiling owing to the shifting of the last whorls to the dorsal side. Typical of these forms along with the uncoiling, is a compression of the chambers in a direction perpendicular to the plane of coiling, which is unusual for globigerinids (figs. 27, 28). The small five-chambered forms encountered here are evidently neogenetic, arising on account of an independent development of juvenile five-chambered stages.] Size: Etymology: Extra details from original publication
Bykova, N. K. (1960). K voprosy O tsiklichnosti filogeneticheskogo razvitiya u foraminifer. Trudy Vsesoyuznego Neftyanogo Nauchno-Issledovatel 'skogo Geologo-Razvedochnogo Instituta (VNIGRI). 163: 309-336. gs
Globigerina praeglobotruncanaeformis compiled by the pforams@mikrotax project teamviewed: 26-9-2022