PTEROTRIGONIIDAE VAN HOEPEN, 1929 SCABROTRIGONIINAE COOPER, 1989

Halligan, William Keith, 2023, Washington State (USA) trigoniids (Bivalvia) from the conglomerate of Patterson Lake (Early Cretaceous), PaleoBios 40 (8), pp. 1-15 : 8

PTEROTRIGONIIDAE VAN HOEPEN, 1929 SCABROTRIGONIINAE COOPER, 1989 NOTOSCABROTRIGONIA DIETRICH, 1933 NOTOSCABROTRIGONIA OREGANA ( PACKARD, 1921)

FIG. 7

Trigonia evansi Meek, 1876, p. 359 , pl. 2, figs. 7, 7a, 7b Trigonia evansana Meek. Packard, 1921, p. 25

Trigonia evansana var. oregana Packard, 1921, p. 26 , pl. 9, fig. 7.

Trigonia . evansana var. oregona Stewart, 1930, p. 93 .

Trigonia deschutesensis Packard, 1921, p. 24 , pl. 10, fig. 3. Trigonia oregona Packard. Anderson, 1958, p. 116 .

Pterotrigonia oregana (Packard) . Jones, 1960b, p. 437, pl. 59, figs. 2, 5, 9, 11-13.

Notoscabrotrigonia oregana (Packard) . Cooper 2015a, pp. 25, 27.

Holotype — Type number 4, Condon Collection, Department of Geology , University of Oregon ( Jones 1960b). Despite multiple searches, the specimen could not be found . Holotype assumed missing.

Plastoholotype— CASG 573 . Cast of the external mold holotype, LV .

Material— UWBM 112553: Silicone cast from an external mold of a nearly complete RV.Missing the beak and some of the escutcheon, anterior and ventral margins. From UWBM loc. B-9486.

Occurrence— Endemic to the Cordilleran Province . Middle Albian to late? Cenomanian ( Jones 1960b). Washington State and Oregon ( USA) .

Description— Shell medium-sized (L = 54mm), crescentic with anterior end much wider than posterior. Strongly inequilateral (umbo anterior and nearly terminal). Shell inflated anteriorly (W/H ≈ 0.34). Prominent umbo with pointed, incurved, opisthogyrate beaks (seen in other specimens from the cPL). Dorsal margin concave, becoming straighter posteriorly. Specimen missing some of the anterior and ventral margins. Posterior terminus bluntly rounded. Inner and outer areas separated by a median groove which is more distinct posteriorly. Both areas unornamented except for transverse growth lines. Escutcheon not well-exposed, but transverse ribs are evident.

Umbo and flank ornamented with about 15 raised,narrow, prominent, sharp ribs that originate at the marginal angulation. They traverse the disk obliquely from the marginal angulation to the anterior and ventral margins, assuming a straight to slightly curved course. The tops of the anterior ribs have small, inconspicuous tubercles. Interspaces are concavely rounded to flat, unornamented except for fine growth lines, and are about twice as wide as the ribs.

Discussion— Meek’s original description (1858) of Trigonia evansana was based on fossils from Vancouver Island, British Columbia ( Canada). In 1876 Meek published another description of the species but (mistakenly?) used the name Trigonia evansi . Although he again cited Vancouver Island as the locality of that species, the gutta-percha cast specimen figured in the study (plate 2, figs. 7a, b) was collected from Crooked River, Oregon ( USA) ( Stewart 1930). Meek’s two species names were considered synonyms ( Packard 1921, Jones 1960b), and pterotrigoniids from the Crooked River were labelled and curated as T. evansana ( Jones 1960b) . Packard (1921) documented differences between the pterotrigoniids from Vancouver Island and Crooked River; he recognized the Crooked River pterotrigoniid as a new variety and assigned it the name, Trigonia evansana var. oregana Packard, 1921 . In his discussion on the topic, Stewart (1930) misspelled the name as “ oregona ” and this mistake was repeated by Anderson (1958). Finally, Jones (1960b) clarified these issues, elevated the Crooked River pterotrigoniid to species level ( oregana ), and assigned it to the genus, Pterotrigonia van Hoepen, 1929 . Cooper (2015a) has since assigned it to another genus: Notoscabrotrigonia Dietrich, 1933 .

According to Jones (1960b), N. oregana is part of an evolutionary series: N. oregana (Middle Albian-Cenomanian[?]) → N. klamathonia ( Anderson, 1958) (Early Turonian-Early Coniacian[?]) → N. evansana (Early Coniacian-Campanian) . Notoscabrotrigonia oregana differs from N. klamathonia in that the latter has more numerous (20-25), finely tuberculate ribs with narrower interspaces. Notoscabrotrigonia oregana differs from N. evansana in that the latter has large, blunt tubercles on the anterior ribs and a narrower area ( Jones 1960b). Although the specimen from Patterson Mountain is not complete, there is enough ornamental detail present to distinguish it from both N. klamathonia and N. evansana .

Figures

Figure 7.Notoscabrotrigonia oregana (Packard, 1921) UWBM 112553 from UWBM loc. 9486. Silicone cast of an external mold. Flank view of RV. Scale bar = 10 mm.