Podocyrtis sinuosa Ehrenberg, 1873, p.253; 1875, pl.15, fig.5; Riedel and Sanfilippo, 1970, p.534, pl.11, figs.3-4; 1978a, text-fig.3
Cephalis [three-lobed], hemispherical, with many small pores, and bearing a three-bladed horn of about the same length. Collar stricture marked by a change in contour, obscure in late specimens. Thorax campanulate (conical in some late specimens); and the abdomen subcylindrical, slightly inflated, both segments with subcircular pores in longitudinal rows usually (but not in some late specimens) separated by longitudinal ribs. Pores of the abdomen larger than those of thorax. Lumbar stricture moderate to slight. Three feet are generally shovel-shaped but spathulate in some late specimens (Riedel and Sanfilippo, 1970).
Thorax in early specimens 55-80 µm long and 85-110 µm wide. Length of abdomen (including feet) in early specimens 125-180 µm, in late specimens 145-225 µm. Maximum breadth of abdomen in early specimens 115-140 µm, in late specimens 135-170 µm (Riedel and Sanfilippo, 1970).
From P. (Podocyrtis) papalis and P. (Podocyrtoges) aphorma, P. (L.) sinuosa differs in having a smaller thorax, and pores of the abdomen larger than those of the thorax. From P. (L.) mitra it differs in having its greatest abdominal width medially rather than distally, and from P. (L.) fasciolata in constantly possessing well developed feet (Sanfilippo et al., 1985).
The thorax, with pores in longitudinal rows usually separated by ribs, is rather constant in structure, though it decreases in size through time. The abdomen is always widest medially, inflated to a varying degree, with longitudinal pore rows separated by ribs, and variability is expressed by an increase in pore size (to approximately double the diameter of the earliest ones) and abdominal length with time (Sanfilippo et al., 1985).
This species occurs in low-latitude (below 30°N in the Atlantic) samples of middle middle Eocene age. It does not occur at DSDP Site 148 in the Indian Ocean, which was at about 45°S during the Eocene according to Firstbrook et al. (1979), but this may be a consequence of the age of the sample rather than of its geographic position. Its evolutionary transition from Podocyrtis acalles lies within the Theocotyle cryptocephala Zone. Its evolutionary transition to Podocyrtis mitra defines the base of the Podocyrtis mitra Zone.
P. (L.) sinuosa apparently evolved from P. (L.) acalles, which in turn developed directly from P. (P.) papalis), and gave rise to P. (L.) mitra. At the time of that transition, P. (L.) trachodes developed as an offshoot, and slightly earlier than that P. (L.) fasciolata and P. (L.) helenae diverged from P. (L.) sinuosa.
Additional illustrations can be found in Riedel and Sanfilippo, 1981, figs.12-8, 1-4.
For generic level taxonomy see Sanfilippo and Riedel, 1992.