Yaadia whiteavesi, (PACKARD, 1921)

Halligan, William Keith, 2023, Washington State (USA) trigoniids (Bivalvia) from the conglomerate of Patterson Lake (Early Cretaceous), PaleoBios 40 (8), pp. 1-15 : 4-6

YAADIA WHITEAVESI ( PACKARD, 1921)

FIG. 5A-C

Trigonia , sp. indt. Whiteaves, 1876, p. 70, pl. 10, fig. 2, 2a. Trigonia leana var. whiteavesi Packard, 1921, p. 21 , pl. 6, fig. 2 only. Trigonia perrinsmithi Anderson, 1958, p. 110 , pl. 2, fig. 7. Trigonia whiteavesi (Packard) . Anderson, 1958, p. 111. Yaadia whiteavesi (Packard) . Saul, 1978, p. 31, pl. 2, figs. 3-5, pl. 3, figs. 1-6, text-fig. 12.

Holotype — GSC Type Collection, Cat. no. 4997.

Figure 5. Yaadia whiteavesi ( Packard, 1921) All are silicone casts of external molds from UWBM loc. 9486. A. UWBM 112550: RV. Dotted line indicates missing escutcheon and part of umbo. B. UWBM 112551: Both valves, complete, butterfly opened. C. UWBM 112556: Schizodont dentition, both valves.

Specimen from the Haida Formation, Queen Charlotte Islands, British Columbia, Canada.

Material— UWBM 112550: Silicone cast from an external mold, RV. Specimen missing the escutcheon and part of the umbo. UWBM 112551: Silicone cast from an external mold of both valves, complete, butterfly opened. UWBM 112556: Silicone cast from an internal mold of the schizodont dentition, both valves. The original internal mold was destroyed in the process of freeing the cast. All specimens from UWBM loc. B-9486.

Occurrence— Endemic to the Cordilleran Province ( Cooper and Leanza 2017). Late early Albian ( Brewericeras hulenense zone) to middle Albian ( Saul 1978). California, Oregon, Washington State ( USA), and British Columbia ( Canada) ( Saul 1978).

Description— Moderately large (L = 81 mm, 98 mm), thick-shelled, subrectangular, equivalve, strongly inequilateral. Longer than high (Average H/L = 0.70), moderately inflated (Average W/H = 0.25). Maximum inflation line follows a line along the first node of each flank rib. Umbo anterior, nearly terminal, opisthogyrate. Dorsal margin nearly straight. Posterior end narrower and more convexly curved than anterior end. Anterior end truncated, forming a gentle convexity from the beak to the corner rib at the junction with the ventral margin. Anterior angulation ornamented with row of prominent nodes that increase in size ventrally. Umbo and flank ornamented with rows of nodes forming ribs that arch slightly anteriorly as they approach the anterior/ventral margins; rib nodes enlarge ventrally and elongate along the growth lines. There is a narrow but definite space between the anterior angulation nodes and the flank ribs. Corner rib has 9-11 nodes. Width of nodes equal to interspaces. Outer and inner areas nearly smooth except for fine growth lines. Marginal angulation nodes smaller than the rib nodes and tend to fade as they approach the posterior margin. Median groove nodes weak and fade 3-4 cm from the beak. Escutcheon angulation lined with a row of small nodes similar to the marginal angulation nodes.

Discussion— This trigoniid is the dominant species of the cPL. Without ornamental detail, it is difficult to distinguish it from its Hauterivian ancestor, Y. jonesi Saul, 1978 , or its Cenomanian descendant, Y. leana ( Gabb, 1876) . Material previously collected from this site was misidentified as Trigonia (Yaadia) leana ( Barksdale 1975, McGroder et al. 1990). Compared to Y.leana , Y. whiteavesi is more elongate, more truncated anteriorly, has more pronounced anterior angulation nodes, and more nodes in the corner rib (9+ vs. 6-7) ( Saul 1978). It differs from Y.jonesi by having a narrower space between the anterior angulation nodes and the flank ribs, a less ornamented area, and rib interspaces that are similar in width to the rib nodes. ( Yaadia jonesi has rib interspaces that are wider than the rib nodes [ Saul 1978].)