Crassatella pedroi, 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 : 670-671

Crassatella pedroi sp. nov.

Fig. 6G .

Etymology: From “Pedro”, informal name for Inkayacu paracasensis , an Eocene penguin unearthed nearby.

Holotype: Articulated paired adult valves: UWBM 101833 , L 38.4, H 30.8, T 8.6.

Type locality: B8341, near Playa Yumaque, East Pisco Basin, Peru.

Type horizon: Very base of Otuma depositional sequence, lower Priabonian.

Material.—B8329, six broken specimens.

Diagnosis.—Anterior of shell compressed. Commarginal ribs extend beyond umbo.

Description.—Shell about 40 mm long, quadrate, anterior compressed, L:H ratio 1.25, T:H ratio 0.2, maximum inflation ventral to beak. Anteriodorsal and posteriodorsal margins straight, anterior margin sharply rounded, posterior margin broadly truncate, ventral margin rounded with slight angulation. Weakly angular posterior ridge diverging 20−25° from posteriodorsal margin. Secondary posterior ridge obsolete. Lunule twice as wide as escutcheon; both about two-thirds the length of respective margins. Beak prosogyrate. Umbo rounded, orthogyrate, with broad commarginal ribs extending ventrally 20 mm; ribs absent posterior to primary posterior ridge. Remainder of exterior with irregular commarginal growth lines. Interior of valves not visible. Inner ventral margin smooth.

Remarks.—Despite the absence of visible hinge characters, the paired specimen of Crassatella pedroi can be distinguished from specimens of C. neorhynchus by its anterior compression ( Fig. 6G 1 ) and commarginal ribs extending well beyond the umbo ( Figs. 6G 2 , G 3 ). Furthermore, the lunule is narrowly cordate ( Fig. 6G 1 ) and both it and the escutcheon are proportionally longer than their counterparts on specimens of C. neorhynchus . The widely spaced umbonal ribs distinguish C. pedroi from the slightly younger C. rafaeli sp. nov. from the Otuma depositional sequence.

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

Figures

Fig. 6. Crassatellid bivalves from the late Eocene of south-central Peru. A−F, H. Crassatella neorhynchus (Olsson, 1931), Paracas depositional sequence. A. UWBM 101826, exterior of left valve. B. MUSM INV 203, left hinge plate. C. MUSM INV 208, dorsal margin, anterior at right. D. MUSM INV 206, dorsal margin, anterior at right. E. UWBM 101828, exterior of left valve. F. UWBM 101823, interior of right valve. H. MUSM INV 212, exterior of left valve, juvenile. G. Crassatella pedroi sp. nov., UWBM 101833, holotype, Otuma depositional sequence; exterior of left (G1) and right (G2) valves, dorsal view of paired valves (G3), anterior at right. 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.

Fig. 3. Crassatelline bivalves from Central and South America. A, B. Kalolophus antillarum (Reeve, 1842). A. UWBM 101885, Recent, Pacific coast of Panama; exterior (A1) and interior (A2) of left valve. B. UWBM 101884, Recent, Venezuela; dorsal view of paired valves, anterior at right. C. Hybolophus berryi (Spieker, 1922), USNM 562399, early Miocene, lower Zorritos Formation, Zorritos, Peru; exterior of left valve (C1), dorsal view of paired valves C2), anterior at right. D. Hybolophus elassa Woodring, 1982, USNM 647424, late Miocene, Gatun Formation, Panama; exterior of left valve.E. Kalolophus mediamaricanus (Brown and Pilsbry, 1913), USNM 647421, early Miocene, La Boca Formation, Panama; exterior of right valve. F. Kalolophus sp., USNM 647423, late Miocene, middle Gatun Formation, Panama; exterior (F1) and interior (F2) of left valve. G. Kalolophus jamaicensis (Dall, 1903), USNM 135683, Pliocene, Bowden Formation, Jamaica; interior of left valve. H. Kalolophus speciosus (Adams, 1854), SBMNH 140817, Recent, Panama City, Florida; exterior (H1) and interior (H2) of left valve; dorsal view of paired valves (H3), anterior at right. Scale bars 10 mm.