Botryostrobus aquilonaris (Bailey)

Eucyrtidium aquilonaris Bailey, 1856, p.4, pl.1, fig.9

Artostrobium miralestensis (Campbell and Clark), Riedel and Sanfilippo, 1971, p.1599, pl.1H, figs.9-13 (partim.); Kling, 1973, p.639, pl.5, figs.31-34 (partim.)

Botryostrobus aquilonaris (Bailey), Nigrini, 1977, p.246, pl.1, fig.1 (with synonymy)

DESCRIPTION

Shell typically heavy, thick-walled, but early forms are not so robust. Constrictions (other than collar and lumbar strictures) unevenly spaced and all strictures usually obscure externally. Shell spindle-shaped with four or five post-cephalic segments, the fourth being widest. Cephalis hemispherical with small irregular pores; vertical tube robust, cylindrical, directed obliquely upwards at ~45. Apical horn very small, needle-like. Thorax inflated with two or three transverse rows of large subcircular pores. Subsequent segments with three to six (usually four) transverse rows of very closely spaced circular pores. Thickness of shell makes each pore appear to have a ring around it. Shell narrows distally, terminating in smooth peristome of variable width; peristome may have single row of pores. Termination smooth or with an undulating margin (Nigrini, 1977).

DIMENSIONS

Based on 20 specimens. Total length 110-155 m; maximum breadth 60-90 m (Nigrini, 1977).

DISTINGUISHING CHARACTERS

This name is used only for very heavy, thick-walled Artostrobiids having multiple segments. It is generally smaller than Botryostrobus miralestensis and has fewer segments and smaller, more closely spaced pores.

DISTRIBUTION

Rare to few from the Stichocorys peregrina Zone to the Holocene. More abundant in middle- and high-latitude sediments. The occurrence of this species subsequent to the extinction of Stylatractus universus defines the uppermost Quaternary zone in middle latitudes. Using Indian Ocean surface sediment samples, Johnson and Nigrini (1980) found a bimodal distribution in which the species is consistently present between 35 and 46S and occurs sporadically between 0 and 20S.

PHYLOGENY

Descendant of Botryostrobus miralestensis.

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