Porterius woodfordi, (Hanna, 1927)

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 : 13-14

PORTERIUS WOODFORDI (M.A. HANNA, 1927)

FIG. 7A, B

Barbatia woodfordi M.A. Hanna (1927) . p. 273; pl. 27, figs. 1, 6, 8, 10.

Porterius woodfordi (Hanna) , Reinhart (1937). pp. 176–178.

Porterius woodfordi (Hanna) , Vokes (1939). p. 45; pl. 1, fig. 13.

Porterius woodfordi (Hanna) , Keen and Bentson (1944), pp. 31, 103.

Porterius woodfordi (Hanna) , Givens (1974), p. 41.

Porterius woodfordi (Hanna) , E.J. Moore (1983), pp. 46–47; pl. 10, figs. 3, 4.

Discussion—A second Paleogene species of Porterius , described from middle Eocene rocks of the Ardath Shale in California, differs from the type species in having finer and more numerous radial ribs with narrower interspaces. The shells of the three specimens in the type lot are relatively thinner, more fragile, as illustrated here ( Fig. 7A ) by a paratype ( UCMP 31063) that was not clearly illustrated by Hanna. Although the types are less well preserved than those of P. gabbi it is fortunate that the hinge two of the primary types preserve the elongate posterior teeth that are parallel to the hingeline, confirming that it is, indeed, a parallelodontid. Only the hinge of the holotype was figured by Hanna, and the hinge of the less well-preserved paratype ( UCMP 31063) is illustrated here ( Fig. 7B ).

Givens (1974) documentation of the geology and molluscan biostratigraphy provides the clearest evidence that the early Eocene occurrence of P. woodfordi is in a mudstone facies in a large tropical marine deltaic complex, in a mudstone facies that “was deposited below wave base in a calm outer sublittoral or bathyal environment” ( Givens 1974, p. 33). This is potentially a warmer deep setting, rare in the Eocene prior to the onset of the global cooling recorded subsequently in the Keasey fauna.

The Eocene geologic setting in southern California is of special interest here because regional tectonic and paleobathymetric interpretations are independent of the molluscan fauna. The Ardath Shale is part of a genetically- related complex of intergrading stratigraphic units that record major Eocene coastal submergence (Kennedy and G.W. Moore 1971). The succession also includes graded beds, submarine slides and benthic foraminifera indicative of outer shelf and slope depths.

Refigured paratype—UCMP 31063.

Locality—UCMP 5062.

Stratigraphic range and age—Paleocene (Cerros Shale member of the Lodo Formation) to lower middle Eocene (Ardath Shale). It is also present in the lower Eocene Juncal Formation.

Figures

Figure 7. Porterius woodfordi (Hanna, 1927), Ardath Shale, paratype UCMP 31063. A. Exterior of with numerous very fine radial ribs, scale bar=1 cm B. previously unfigured cardinal area and hingeplate, scale bar=1 mm.