Antillipecten quemadosensis Waller, 2011
WALLER, T. R. 2011. Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley. Bulletins of American Paleontology, 381: 1-197, pls. 1-18. [p. 117, pl. 17, figs. 4-10]
2011 Antillipecten quemadosensis Waller, 2011
T. R. Waller, 2011, plate 17.
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«Diagnosis.— Antillipecten with equilateral, slightly right-convex shell, with 10-13 evenly spaced major radial ribs; posteriormost rib of RV consisting of two smaller ribs because of bifurcation in early ontogeny; ribs high with rounded crests and steep sides; secondary costae intercalated in rib interspaces in early ontogeny but absent from rib crests throughout ontogeny; posterior margin of posterior auricles forming acute angle with dorsal margin, all auricles radially costate; byssal notch moderately deep with active ctenolium.
Description.— Shell small, not known to exceed 26 mm Ht, equilateral, acline to slightly prosocline, Ht slightly exceeding L except in latest ontogeny, when Ht and L are approximately equal; umbonal angle 92-102°; both valves only moderately convex with RV more convex than LV; hinge line short (hl/L= 0.6-0.7), anterior hl very slightly greater than posterior hl. Disks with 10-13 ribs; ribs originating as low undulations in early ontogeny after early smooth zone, becoming high, rounded, steep-sided in late ontogeny; ribs of even height and spacing in central sector, decreasing in height and width toward disk flanks; posteriormost rib of RV commonly consisting of two riblets near margin due to bifurcation early in ontogeny; secondary costae intercalating in interspaces in early ontogeny, with 3-5 in interspaces in late ontogeny; crests of major ribs rounded, without secondary costae. Commarginal lamellae of close-set decatopectinine type present on both ribs and interspaces, commonly with higher lamellae forming periodically in interspaces in early ontogeny, separating groups of finer lamellae; lamellae passing straight across ribs and interspaces but with ventrally convex curvature over tops of secondary costae; projecting scales absent. Disk flanks low, steep, lacking radial costellae. Auricles of moderate size relative to size of disk; right anterior auricle with 4 or 5 strong, slightly scabrous radial costae, broad byssal fasciole, and moderately deep byssal notch with persistent active ctenolium; left anterior auricle with from 5-9 radial costae, rounded anterior margin, and moderate deep byssal sinus; posterior auricles with 5-9 radial costae beginning in mid-ontogeny after early noncostate zone. Hinge dentition weak, dominated on RV by dorsal teeth, intermediate and resilial teeth absent. Striate and nonstriate adductor scars of RV separated on anterior side by deep groove. Foliated-calcite re-entry of RV entering adductor separation and bordering posteroventral margin of nonstriate adductor scar. Edges of ribs on shell interior carinate near shell margin. Interior features of LV not observed. Etymology.— Named after the town of Los Quemados, Dominican Republic, a short distance east of the type locality. Holotype and measurements.— USNM 541016 (Pl. 17, Figs 4-7), a pair of closed but slightly off set valves, 26.0 mm Ht, 24.0 mm L, paired valves 8.5 mm cvx. Type locality.— Locality TU 1278, large arroyo on eastern side of Río Gurabo just at the ford on Los Quemados-Sabaneta Road, Gurabo Formation, Upper Miocene. Saunders et al. (1986: text-fig. 4) showed locality NMB 15836, which is in approximately the same position as TU 1278, as being 387-389 m above the base of the Río Gurabo section and a short distance below the Miocene-Pliocene boundary. Other material.—19 specimens from 11 localities in the northern Dominican Republic (Table 22). All but two of these are single valves. Remarks.—Among the limited number of specimens on hand, Antillipecten quemadosensis n. sp. has a fairly constant morphology with the exception of the specimens from the Guayubín area (TU 1281). Th e single right valve from TU 1281 has only 11 ribs, whereas right valves from other localities have 12 or 13. Similarly, left valves from other localities have 11-14 ribs, but two or the three left valves from TU 1281 have only 10; the third has 11. Furthermore, the posterior auricular costae on specimens from TU 1281 are fi ner and more numerous than are those on specimens from other localities. Antillipecten quemadosensis n. sp., like its extant counterpart A. antillarum, probably had a broad depth range. Its association with Argopecten thetidis at four of the eight localities and particularly its association with Gurabopecten uniplicatus n. gen., n. sp., at TU 1278 indicate that the species ranged into waters > 50 m. Comparisons.— Antillipecten quemadosensis n. sp. is closest in morphology to the extant species A. antillarum. The two species have the same shape and range in number of ribs but differ in rib height and distribution of secondary costae. Antillipecten quemadosensis n. sp. has much higher ribs that have steeper sides. Its secondary costae are limited to the rib interspaces, and the rib crests are evenly rounded and noncostate. In A. antillarum, costae are commonly present on the rib crests, the fi rst expression of these rib-top costae being a very low medial ridge in the center of the crest. Additional secondary costae develop on the rib crests in later ontogeny. On some specimens, these costae are low and barely discernible under oblique light; on others they are well-developed, exemplifi ed by specimens from St. Thomas, Virgin Islands [USNM(IZ) 103043, Pl. 16, Figs 1, 3]. Antillipecten cercadicus diff ers from A. quemadosensis n. sp. in having a broader, more fl aring shell with more ribs (16 or 17) and in lacking secondary radial costae. In early ontogeny, A. cercadicus has raised commarginal lamellae that separate groups of close-set lamellae, the raised lamellae extending across the rib crests whereas the fi ner lamellae do not. Antillipecten quemadosensis n. sp. has lamellae of two orders in early ontogeny, but the major lamellae do not cross the rib crests. Antillipecten janicoensis n. sp. resembles A. quemadosensis n. sp. in having secondary costae limited to rib interspaces. In A. janicoensis n. sp., however, the ribs are more numerous (15-17 compared to 10-13 in A. quemadosensis n. sp.) and the correspondingly narrower interspaces support fewer secondary costae, commonly only 1 or 2. Antillipecten janicoensis n. sp. also differs from A. quemadosensis n. sp. in having more delicate posterior auricular costae, which are limited to the ventral part of each posterior auricle. Evolution.-- Antillipecten quemadosensis n. sp. is probably ancestral to the extant species, A. antillarum, but the number of specimens of A. quemadosensis n. sp. available is too small to permit detecting any stratigraphic changes in morphology. The change to A. antillarum occurred at least by the time of deposition of the Bowden Beds of Jamaica, the age of which is now regarded as late Middle Pliocene (late Piacenzian; Kohl & Robinson, 1998). The ancestry of A. quemadosensis n. sp. is poorly constrained by the specimens on hand. A possible ancestor is A. janicoensis n. sp., which occurs mainly or entirely in the Cercado Formation, whereas A. quemadosensis n. sp. occurs in the Gurabo Formation. Both species have costate interspaces, noncostate rib crests, and a doubling of the lateralmost disk ribs in early ontogeny. Occurrence.— In the northern Dominican Republic, Antillipecten quemadosensis n. sp. is widely distributed among river sections and road cuts in the Gurabo and lower? Mao formations in strata determined by Saunders et al. (1986) to be Late Miocene to Pliocene in age. Distribution.— Antillipecten quemadosensis n. sp. has not yet been found with certainty outside of the Dominican Republic. A careful search of the extensive collections from Neogene formations in the southeastern United States housed in the Smithsonian Institution turned up nothing. A search of the less extensive collections from the Antilles turned up only a single disk fragment from the Aymamon Formation of Puerto Rico (locality USGS 17207) of possible Middle Miocene age (Renken et al., 2002: pl. 24), but both the taxonomic identity of the specimen and the age of the Aymamon Formation are uncertain.» THOMAS RICHARD WALLER, 2011
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