Thyrsocyrtis (Thyrsocyrtis) tarsipes Foreman

Thyrsocyrtis tarsipes Foreman, 1973, p.442, pl.3, fig.9, pl.12, fig.14; Sanfilippo and Riedel, 1982, p.174, pl.1, figs.1-2

DESCRIPTION

Subcylindrical form. Small, spherical cephalis with moderate number of small pores and cylindro-conical horn of usually 2-3 times its length. Thorax campanulate to inflated, usually as wide as, or wider than abdomen, with circular, close-packed pores. Vestigial wings commonly present halfway down the segment. Lumbar stricture usually distinct. Abdomen annular to short cylindrical, with pores generally less regular than those of thorax. Feet tapering from peristome, subcylindrical, irregularly and finely perforate, usually divergent (Sanfilippo and Riedel, 1982).

DIMENSIONS

Based on 10 specimens. Length excluding horn 180-230 m, of cephalothorax 75-95 m, of abdomen 35-55 m. Maximum breadth 80-105 m (Sanfilippo and Riedel, 1982).

DISTINGUISHING CHARACTERS

T. tarsipes is distinguished from its descendant, T. hirsuta, in its generally smaller size and porous feet (Sanfilippo et al., 1985).

VARIABILITY

The campanulate to inflated thorax commonly bears three vestigial wings. The cylindrical to slightly inflated abdomen is rounded-triangular in cross-section, shorter than, and of approximately the same width as the thorax. Abdominal pores are generally irregular in size and shape, as large to twice as large as those of the thorax, and more widely spaced. The three feet vary in length, and are irregularly perforated (Sanfilippo et al., 1985).

DISTRIBUTION

T. tarsipes occurs in Paleocene to early early Eocene sediments from the Atlantic (DSDP 384), the Caribbean and the Gulf of Mexico from 15S to 30N. Its morphotypic first appearance has not been determined. Its morphotypic last appearance lies within the Buryella clinata Zone.

PHYLOGENY

T. tarsipes, or an ancestor common to both, apparently gave rise to T. hirsuta.

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