Crassatella rafaeli, Devries, 2016

Devries, Thomas J., 2016, Fossil Cenozoic crassatelline bivalves from Peru: New species and generic insights, Acta Palaeontologica Polonica 61 (3), pp. 661-688 : 671

Crassatella rafaeli sp. nov.

Fig. 7 .

Etymology: Named in recognition of Rafael Casas, driver and desert guide in the East Pisco Basin.

Type material: Holotype, adult right valve with exposed hinge and missing posterior: UWBM 101834 , B8344, L (61.0), H (60.2), T 22.0 . Paratypes: UWBM 101835 , B8353, L 57.3, H 42.6, T 14.3; UWBM 101836 , B8352, L 50.2, H 38.5, T 12.2; UWBM 101837 , B8352, L 35.3, H 27.3, T 9.8; UWBM 101838 , B8352, L (38.5), T 14.8; UWBM 101839 , B8352, L (36.3), H 37.9, T 13.6; UWBM 101840 , B8352, L (37.6), H 36.7, T 14.3; UWBM 101841 , B8342, L 34.4, H 29.0, T 10.0; UWBM 101842 , B8342, H (29.9), T 10.1; MUSM INV 210 , B8334, L (55.8); MUSM INV 211 , B8353, L 51.7, H 41.6, T 14.9; MUSM INV 212 , B8352, L 45.3, H 36.6, T 10.6; MUSM INV 213 , B8352, L (35.5), H (32.4), T 11.4; MUSM INV 214 , B8352, L (35.4), H (31.5); from B8334, B8342, B8352, B8353; plain 4−10 km north of mine overlooking Bajada del Diablo , all material from the East Pisco Basin, Peru .

Type locality: B8344, 4 km north of mine that overlooks Bajada del Diablo , East Pisco Basin, Peru .

Type horizon: Lower Otuma depositional sequence, Priabonian .

Material.—Additional specimen from B8349, East Pisco Basin, Peru.

Diagnosis.—Umbo with closely spaced commarginal ribs. Resilifer extending half way or entirely to vmHP. Large specimens with crenulate inner ventral margin.

Description.—Shell to 80 mm long, elongate-ovate, L:H ratio 1.2, T:H ratio 0.3, maximum inflation ventral to beak. Anteriodorsal and posteriodorsal profiles usually slightly concave, anterior and ventral margins broadly rounded, posterior margin bluntly truncate, produced. Angular primary posterior ridge diverging 20−25°, weak secondary posterior ridge 5° from posteriodorsal margin. Lunule cordate, twice as wide as escutcheon; both about half the length of respective margins. Beak prosogyrate. Umbo rounded or slightly flattened, prosogyrate, with closely spaced commarginal ribs that disappear posterior to primary posterior ridge. Remainder of exterior with irregular commarginal growth lines. Resilifer extending half way or nearly entirely to vmHP. Left anterior cardinal tooth short, thick, wedge-shaped, inclined anteriorly 30°, separated from beak by lunule. Left posterior cardinal tooth wedge-shaped, inclined posteriorly 10°. Receptor pit absent. Right anterior pseudocardinal tooth lamellar, inclined anteriorly 70°, joining right cardinal tooth and lunule. Right cardinal tooth thick, wedge-shaped, inclined anteriorly 10°. Right posterior pseudocardinal tooth diverging 55° posteriorly from cardinal tooth, passing resilifer ventrally. Inner ventral margin crenulate in large specimens.

Remarks.–Specimens of Crassatella rafaeli are distinguished from those of the slightly older C. neorhynchus and C. pedroi by their closely spaced commarginal ribs on the umbo ( Fig. 7F 1 ). Large specimens of C. rafaeli become increasingly elongate and produced ( Fig. 7F 2 , G). The crenulate ventral margin on the largest specimens is also visible externally as anteriodorsally-oriented parallel subsurface lineations that fade dorsally ( Fig. 7C ). Irrespective of shell size, some resilifers extend nearly fully from the beak to the vmHP ( Fig. 7E, G ). In contrast, for all specimens of all species of the younger Tilicrassatella , resilifers are broader and always extend entirely to the vmHP or nearly so.

Stratigraphic and geographic range.—Priabonian, Otuma depositional sequence, East Pisco Basin, south-central Peru.

Figures

Fig. 7. Crassatellid bivalve Crassatella rafaeli sp. nov. from the late Eocene, Otuma depositional sequence, south-central Peru. A. UWBM 101834, exterior A1), and interior (A2) of right valve. B. UWBM 101838, right hinge plate.C. MUSM INV 210, fragment of anterioventral margin showing striations terminating in marginal crenulations. D. UWBM 101840, interior of left valve with resilifer extending half way to the vmHP. E. MUSM INV 213, interior of left valve with resilifer reaching nearly to the vmHP. F UWBM 101836, dorsal margin of paired valves (F1), anterior to right, exterior of right valve (F2). G. UWBM 101835, interior of right valve. H. UWBM 101837, exterior of right valve. Abbreviation: vmHP, ventral margin of the hinge plate. Scale bars 10 mm.

Fig. 1. Forearc basins in Peru with crassatelline-bearing Cenozoic deposits. A. Talara Basin of northern Peru. B. Location of three crassatelline-bearing Peruvian forearc basins. C. East Pisco Basin of south-central Peru. Dashed black line marks the inferred boundary between the East and West Pisco basins. D. The much smaller Sacaco Basin of southern Peru.

Fig. 2. Hinge characters and other features of crassatellines. A, B. Crassatella vadosa Morton, 1834, Cretaceous. A. USNM 450460, Mississippi, USA. B. USNM 451089, Alabama, USA. C. Eucrassatella kingicola (Lamarck, 1805), UWBM 101886, Recent, Victoria, Australia. D. Hybolophus gibbosus Sowerby, 1832), SBMNH 213002, Recent, Gulf of California, Mexico.E. Hybolophus fluctuatus (Carpenter, 1864), SBMNH 137784, Recent, Santa Catalina Island, California. Left valves (A, C1, D1, E), right valves (B, C2, D2), valve in dorsal view (D3). Abbreviation: vmHP, ventral margin of the hinge plate.