The Braarudosphaeraceae are an enigmatic group of nannoliths ranging
from the Early Cretaceous to the present day. Despite being extant they
have never been succesfully cultured and so their afinities are
uncertain (they may be Haptophytes, Dinophytes or belong to another
group). They are of minimal biostratigraphic value but occasionally
occur in enormous abundance, most notably in the Early Danian just
after the K/T boundary and in the Oligocene of the South Atlantic.
Update: Although Braarudosphaera
has still not been succesfully cultured, despite repeated attempts,
Takano et al. (2006) have obtained DNA sequences from single-cell
isolations. These showed that Braarudosphaera is a haptophyte and falls inside the coccolithophore clade.
Informal taxon-based term: Pentalith {Gran and Braarud
1935} - nannolith formed by the Braarudosphaeraceae (N.B. does not
include other nannoliths formed of five elements, such as Discoaster pentaradiatus).
Lamina
plate-like sub-element of segments.
Segment
one of the five component parts of a pentalith. They appear to be single crystal-units, with tangential c-axis orientation.
TERMINOLOGY
