Neilo altamirano, Kiel & Hybertsen & Hyžný & Klompmaker, 2020

Kiel, Steffen, Hybertsen, Frida, Hyžný, Matúš & Klompmaker, Adiël A., 2020, Mollusks and a crustacean from early Oligocene methane-seep deposits in the Talara Basin, northern Peru, Acta Palaeontologica Polonica 65 (1), pp. 109-138 : 110-111

Neilo altamirano sp. nov.

Fig. 2A .

Zoobank LCID: urn:lsid:zoobank.org:act:4A36FC09-E842-43D3-9DFC-D55D9A246345

Etymology: In honour of Ali Altamirano (Lima, Peru), for his help collecting the fossils.

Holotype: NRM Mo187001, an internal and external mold of LV, with some shell material preserved.

Type locality: Cerro La Salina (block 1), northern Peru.

Type horizon: Presumably the early Oligocene part of the Heath shale.

Material.— Type material only.

Diagnosis.—Well-inflated, subrectangular shell, tallest at umbo, strongest inflation at posterior third; anterior margin truncate, straight; posterior margin straight; posterior ridge well defined; sculpture of irregularly spaced, blunt commarginal ribs, interspaces roughly twice the width of the ribs.

Dimensions (in mm).— The holotype NRM Mo187001, L = 20, H = 12, and the single valve ca. 4 mm thick .

Description.—Shell subrectangular, well-inflated, postumbonal part about 2/3 of shell length, maximum shell height at umbo; anterodorsal margin slightly convex, anterior margin truncate and straight, ventral margin slightly convex due to angulation opposite of umbo, posterior margin truncate, posterodorsal margin very slightly concave. Posterior area defined by ridge running from behind umbones to posteroventral corner; sculpture consists of irregularly spaced, blunt, commarginal ribs, with fine commarginal lines between; these ribs bent sharply upward at posterior ridge. Distinct groove internally from umbo to anteroventral margin; anterior adductor muscle scar oval and just anterior to this groove, posterior adductor muscle scar indistinct; hinge with row of taxodont teeth.

Remarks.—No Neilo species were reported from the Eocene to Miocene deposits in Peru and Ecuador so far. Quite similar in shell outline and sculpture are Neilo ortmanni Erdmann and Morra, 1985 , from the late Eocene to early Oligocene San Julián Formation in eastern Patagonia ( Argentina) and Neilo ornata ( Sowerby, 1846) from late Oligocene–early Miocene sediments near Puerto Deseado in eastern Patagonia ( Erdmann and Morra 1985; Del Río and Camacho 1998; Griffin and Nielsen 2008). Both species differ from N. altamirano by their rostrate posterior margin, whereas N. altamirano has a vertically truncated, almost straight posterior margin. The early Miocene Neilo volckmanni ( Philippi, 1887) from the Navidad Formation in Chile is quite different by having a pentagonal outline and a distinctive change in sculpture from indistinct anterior of the diagonal posterior ridge to granular-commarginal on the posterodorsal side of the shell. Neilo awamoana Finlay, 1926 , a species common in the offshore siltstone facies of the early Miocene of New Zealand, is similar in outline, but has more numerous, finer, and more closely spaced collabral ribs, and a fine ridge running along the angulation from the umbo to the posteroventral margin ( Beu and Maxwell 1990: pl. 16a, c). The late Oligocene to early Miocene Neilo sinangula Finlay, 1926 , from New Zealand lacks this fine ridge ( Finlay 1926; Marshall 1978; Eagle and Hayward 1993), but also has finer and more numerous commarginal ribs compared to N. altamirano . The early Oligocene Neilo funiculata Hutton, 1887 from New Zealand has a much longer anterior part of the shell than N. altamirano sp. nov. ( Beu et al. 2012).

Stratigraphic and geographic range.— Type locality and horizon only.

Figures

Fig. 2. Protobranch and pteriomorph bivalves from early Oligocene seep deposits from the Cerro La Salina (block 1, A; block 6, D; block 9, C) and Belén seep deposit (B), Talara Basin, northern Peru. A. Malletiid Neilo altamirano sp. nov. (NRM Mo187001, holotype), internal mold in lateral view (A1); external mold in lateral view (A2), arrows indicating the posterior ridge; view on the dorsal side (A3); close-up on the taxodont hinge dentition (A4). B. The possible nuculid Acila? sp. (NRM Mo187002), external mold of outer shell surface. C. The bathymodiolin Idas sp. (NRM Mo187003), internal mold of the entire specimen (C1), arrow indicating the taxondont teeth; close-up on taxodont teeth on posterodorsal shell margin (C2). D. Propeamussiidae indet. (NRM Mo187004), uncoated specimen showing internal radial ridges (D1); specimen coated with ammonium-chloride, highlighting external sculpture (D2).