Glycymeris winlockensis, EFFINGER, 1938

Hickman, Carole S., 2023, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part II: The pteriomorphs, PaleoBios 40 (5), pp. 1-51 : 16

GLYCYMERIS WINLOCKENSIS EFFINGER, 1938

FIG. 9C, D

Glycymeris winlockensis Effinger (1938) . pp. 366–367; pl. 45, figs. 2, 5.

Glycymeris winlockensis Effinger, Weaver (1943) . p. 61; figs. 6, 13.

Discussion — Glycymeris winlockensis differs from the more common Glycymeris andersoni in its subtrigonal outline, with more prominent beaks and sloping rather than rounded dorsal hinge margin. Although radial ribs typically are not preserved on the shell exterior, they are sometimes visible where corrosion has not removed the thin exterior layer ( Fig. 9C ). All known specimens are smaller than the largest shells of the more common G. andersoni , and differences in dorsal slope angle in the available specimens suggest allometric decrease in the angle ( Fig. 9C, D ). More specimens are required for an accurate assessment.

Although the two species co-occur in the jumbled shellbeds at locality UCMP IP2289 and 2548, it is hypothesized that in life they occupied different habitats and depths, co-occurring allochthonously only because of the short-distance downslope transport event suggested above.

Material examined — two specimens from Loc. UCMP IP2289 .

Type information —Figured hypotypes, both from Loc. UCMP IP2289 : UCMP 110734 , length 18.8 mm, height 18.2 mm; UCMP 110735 , length 10.0 mm, height 9.9 mm.

Stratigraphic occurrence —This species is known only from the Gries Ranch Formation. It is not present in the tropical Eocene fauna of the underlying Cowlitz Formation. Glycymeridids are absent from the younger recovery faunas of the Pittsburg Bluff and Eugene Formations of the Pacific Northwest.

Figures

Figure 9. Comparison of dorsal slope angles in Juvenile and adult shells of Glycymeris andersoni Dickerson (1917) and Glycymeris winlockensis Effinger (1938), Gries Ranch Formation. A. Adult G. andersoni hypotype UCMP 110732, scale bar=1 cm. B. Adult G. winlockensis hypotype UCMP 110734, scale bar=1 cm. C. Juvenile G. andersoni hypotype UCMP 110733, scale bar=5 mm. D. Juvenile G. winlockensis hypotype UCMP 110735, scale bar=5 mm.