CRETACEOUS ORIGINATION OF ZEAUVIGERINA AND ITS RELATIONSHIP TO PALEOCENE BISERIAL PLANKTONIC-FORAMINIFERA

Previous identification of Chiloguembelina and Zeauvigerina in Maastrichtian deep sea sediments has contrasted with the generally held view that both taxa evolved during the early Danian. Test dissection and biometric study of test outlines and growth trajectories now reveal that the Southern Ocean forms previously assigned to Chiloguembelina waiparaensis Jenkins, Zeauvigerina teuria Finlay, and some specimens of C. crinita (Glaessner) all belong to Zeauvigerina waiparaensis (Jenkins), a species originally described from the Danian of New Zealand, In addition to the sensu stricto concept of this species, four ''forma'' of Z. waiparaensis are described and illustrated here, Two of these forma (Z. waiparaensis forma improcera and Z. waiparaensis forma prolata) are considered immature growth stages and the other two (Z. waiparaensis forma velata and Z. waiparaensis forma palmula) are considered ecophenotypes, In the southern Indian Ocean and Southwest Pacific, Z. waiparaensis appears just below the first occurrence of Abathomphalus mayaroensis, a zonal marker for the upper Maastrichtian, Simultaneous appearances of this species on both sides of Australia lends support to speculation that marine communication had been established between Antarctica and Australia by Maastrichtian time, Zeauvigerina waiparaensis first appears within the Danian in the Weddell Sea sector of the Southern Ocean, It is not clear why the first appearances are earlier in the southern Indo-Pacific region than in the southern South Atlantic, as preservation is moderate to good at all sites and no physical barrier to marine communication between the sites is apparent. Based on differences in the growth patterns, test shape, and apertural morphology of Z. waiparaensis and Chiloguembelina midwayensis (Cushman), the type species of Chiloguembelina, Zeauvigerina and Chiloguembelina are not considered as sharing a close phylogenetic relationship. Although in this study Zeauvigerina is presumed to have evolved from Laeviheterohelix during the late early Maastrichtian, no ancestral forms with an intermediate morphology have been identified, Biometric similarities between Z. waiparaensis and younger Paleocene species of Zeauvigerina indicate that these belong in the same monophyletic group. This study adds Z. waiparaensis to the well documented species of Hedbergella and Guembelitria that survived the Cretaceous/Tertiary boundary extinction event and gave rise to Tertiary planktonic foraminiferal lineages, Unlike those other survivor taxa, however, the zeauvigerinid plexus did not play an important role in the Danian radiation of planktonic foraminifera,