Hybolophus maleficae, 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 : 678

Hybolophus maleficae sp. nov.

Fig. 10A− G .

Etymology: From Latin malefica, witch; referring to the “La Bruja” witch in Spanish), vertebrate level ( Muizon and DeVries 1985), in which many specimens of this species were found.

Type material: Holotype, complete adult left valve with hinge exposed: UWBM 101858 , B8338, L 44.5, H 38.8, T 11.4 . Paratypes: UWBM 101859 , B8338, L (25.2), H (18.0); UWBM 101860 , B8338, L (24.3), H (16.1); UWBM 101861 , B8338, L 37.0, H 29.4, T 10.0; UWBM 101862 , B8312, L 57.9, H 41.9, T 13.0; UWBM 101863 , B8312, L 35.9), H 31.5, T 10.1; UWBM 101865 , B8312, L (41.0), H 36.2, T 12.7; MUSM INV 219 , B8338, L 37.3, H 30.1, T 9.8; MUSM INV 220 , B8338, L 24.9, H 18.7, T 6.6; MUSM INV 221 , B8338, L 35.6, H 27.1, T 9.0; MUSM INV 222 , B8312. L 54.8, H 43.7, T 13.2; MUSM INV 223 , B8312, L 45.6, H 36.0, T 12.3. From B 8338, B8312, Filudo depression, west of Pozo Santo , East Pisco Basin, Peru .

Type locality: B8338, knoll southwest of Cerro de Amara , Ica valley, East Pisco Basin, Peru .

Type horizon: Lower Pisco depositional sequence, Serravallian .

Material.—UWBM 101864, B8343, L (43.3), H 51.7, T 16.0; UWBM 101866, B8323, L 58.2, H 47.0, T 14.2; UWBM 101867, B8323, L 49.5, H 40.4, T 13.7; UWBM 101868, B8323, L 44.4, H 36.6, T 9.6; MUSM INV 231, B8323, L 48.0, H 37.9, T 11.5; MUSM INV 232, B8323, L (36.1); MUSM INV 233, B8356, L (39.5). Other specimens from B8307, B8310, B8316, B8321, B8335, B8345, B8350, B8351. All material from the East Pisco Basin, Peru.

Diagnosis.—Shell ovate. Resilifer narrow. Left anterior cardinal tooth separated from beak by lunule.

Description.—Shell to 70 mm long, trapezoidally ovate, moderately inflated, posterior variably elongate and produced, beak located two-fifths of length from anterior end, L:H ratio 1.2, T:H ratio 0.3, maximum inflation ventral or anterior to beak. Anteriodorsal and posteriodorsal profiles straight or slightly concave. Anterior margin rounded to bluntly rounded, ventral margin rounded and slightly angled, posterior margin bluntly truncate or produced. Moderately angular primary posterior ridge diverging 20° from posteriodorsal margin. Weak secondary posterior ridge nearly coincident with escutcheon margin. Lunule cordate, half the length of anteriodorsal margin. Escutcheon two-thirds the length of posteriodorsal margin, narrow, one-third width of lunule. Beak prosogyrate. Umbo flattened, prosogyrate to opisthogyrate with widely spaced commarginal ribs, latter sometimes extend ventrally across anterior of valve; remainder of exterior with irregularly spaced commarginal growth lines. Resilifer narrow. Left anterior cardinal tooth short, wedge-shaped, inclined anteriorly 30–35°, separated from beak by lunule. Left posterior cardinal tooth narrower, nearly orthocline. Right anterior pseudocardinal tooth short, diverging from lunule margin. Right cardinal tooth short, straight, wedge shaped, inclined anteriorly 20°. Right posterior pseudocardinal tooth lamellar, diverging 20° posterioventrally from midpoint of cardinal tooth. Inner ventral margin smooth.

Remarks.—Specimens of Hybolophus maleficae , like those of H. picaderus , have a left anterior cardinal tooth separated from the beak by the lunule, a character state not seen in specimens of the Peruvian Miocene H. terrestris sp. nov. and H. nelsoni and the younger Peruvian species, H. gibbosus . Otherwise, the smooth ventral margin and full-length resilifer are typical of posteriorly elongate Hybolophus . In the Filudo depression, strata with specimens of H. maleficae overlie by only a few meters beds with specimens of Tilicrassatella torrens . Hybolophus maleficae appeared in the East Pisco Basin at the same time as Turritella infracarinata and Anadara sechurana Olsson, 1932 , two species with well established fossil records in the Talara and Sechura basins of northern Peru ( Olsson 1932). Together, these species and others constituted a transitional fauna, younger than a Chilcatay fauna (with Tilicrassatella and many species also known in central Chile; DeVries and Frassinetti 2003) and older than an “early modern” fauna (with Hybolophus and many genera still extant in the modern Panamic Province of tropical western America).

Stratigraphic and geographic range.—Serravallian, lower Pisco depositional sequence, East Pisco Basin, south-central Peru. Tortonian, Pisco Formation, Sacaco Basin, southern Peru.

Figures

Fig. 10. Hybolophus crassatellines from Peru. A−G. Hybolophus maleficae sp. nov., middle Miocene, Pisco depositional sequence, south-central Peru. A. UWBM 101862, paratype, exterior of left valve. B. UWBM 101858, holotype, interior of left valve. C. UWBM 101860, paratype, interior of left valve. D. MUSM INV 222, paratype, exterior of left valve. E. UWBM 101864, dorsal margin of paired valves, anterior at right. F. UWBM 101859, paratype, interior of right valve. G. UWBM 101865, dorsal margin of paired valves, anterior at right. H, J, K. Hybolophus gibbosus (Sowerby, 1832), early to middle Pleistocene, tablazos, northern Peru. H. OSU 37600, exterior (H1) and interior (H2) of right valve. J. OSU 37597, exterior (J1) and interior (J2) of left valve. K. OSU 37601, dorsal margin of left valve, anterior at left. I. Hybolophus nelsoni (Grzybowski 1899), USNM 562398, late Miocene, Quebrada Heath, northern Peru; exterior of right valve. Scale bars 10 mm.