Lyropecten dumblei (Gardner, 1945)
GARDNER, J. 1945. Mollusca of the Tertiary formations of northeastern Mexico. Geological Society of America Memoir, 11: 1-332, pls. 1-27. [p. 69, pl. 11, figs. 4, 6]
1945 Chlamys (Nodipecten) dumblei Gardner, 1945
J. Gardner, 1945, plate 11.
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«Pecten condylomatus DALL? of the check lists of Dumble and others.
Not Pecten (Nodipecten) condylomatus Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 729, pI. 34, figs. 14, 15, 1898. Shell of moderate dimensions for the group, rather strongly convex, the beaks central or slightly anterior; apparent convexity affected by the knuckling of the valves, a character that varies widely in degree and position. Radials strong, rounded, slightly wider than the interradials, which are squarish in the region of the umbones but broadly U-shaped toward the ventral margin; a secondary threading developed on the fluted disk, the number running 10 to 12 to a unit of radial and interradial; entire radially sculptured surface overridden with scaly growth laminae. Submargins smooth and high. Ears small, sharply defined, threaded with 6 to 8 subequallirae overridden by incrementals. Byssal notch deep. Ctenolium coarse. Resilifer small, trigonal, subumbonal, marginalligament grooves shallow. Crurae fairly strong but rude, one set subparallel to the margins of the resilifer, the other at a low angle to the dorsal margins. Muscle scar very large. Pallial line remote from the strongly fluted ventral margin. DIMENSIONS: Height of right cotype, 45.0 millimeters; of left cotype, 51.0 millimeters. Width of right cotype, 50.0 millimeters; of left cotype, 59.0 millimeters. Convexity of both right and left cotypes including knuckling, 17.0 millimeters. TYPE MATERIAL: Two cotypes, a right valve, U. S. Nat. Mus. 494994, and a left valve of another individual, U. S. Nat. Mus. 494995; and two paratypes, the larger, U. S. Nat. Mus. 494955, and the smaller, U. S. Nat. Mus. 494956. TYPE LOCALITY: Cotype, right valve, from U.S.G.S. sta. 13455, left valve from U.S.G.S. sta. 13585; larger paratype from U.S.G.S. sta. 13455, smaller paratype from U.S.G.S. sta. 13587. Guajalote formation. The average dimensions are higher than those of the types, and many valves are 60 millimeters high and 65 wide. Though the species was abundant, perfect shells are extremely rare. The hinge devices were not very strong apparently, and the valves were separated and rolled about; the edges of many of them were chipped, and most of them were embedded in a highly tenaceous matrix. The Nodipectens from the Guajalote formation were included in the early check lists of the San Fernando and Tuxpan faunas under Pecten condylomatus, described from the Chipola formation. Both species vary in size, degree of knuckling, and number of ribs, and the end members approach one another closely. The Mexican forms average larger, are less irregular in outline, and have a higher average rib count. They are similar to Nodipectens from the later Alum Bluff, particularly those from White's Creek which is probably early Shoal River in age. Imperfectly preserved specimens from the lower Miocene of Trinidad, U.S.G.S. Sta' 8299, may be identical with N odipecten dumblei. DISTRIBUTION: Guajalote formation: U.S.G.S. sta. 13584 (V-29); U.S.G.S. sta. 13585 (V-29); U.S.G.S. sta. 13587 (W-30); U.S.G.S. sta. 13588 (W-30).» JULIA GARDNER, 1945
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«Syntypes.— USNM 494994 a right valve, 4.5 cm high, 5.0 cm long. USNM 494995, a left valve with one prominent ledge or change in shell profile at 1.8 cm high, emphasized
by three hollow nodes or thickenings. 5.1 cm high, 5.9 cm long. Type locality.— Tamaulipas, Mexico, east bank of Rio Conchos, near town of San Fernando (USGS 13455, USGS 13585). Lower Miocene, Guajalote Formation. Paratypes.— USNM 494955, a left valve measuring 4.5 cm high, 4.9 cm long (USGS loc. 13455). USNM 494956, an atypical left valve with three rounded ledges and broken anterior auricles, 3.5 cm high, 3.7 cm long (USGS loc. 13587). Significant hypotype.— UCMP 37395, a double-valved specimen from the type area (UCMP D-8799). Description.— Adult valves equally convex, juvenile left valves flatter than right valves. Profile variable; right valve rounded, left valve commonly with a single angular ledge at about 2 cm high (but some specimens have two or three ledges). Valves circular in juvenile stages, longer than high in adults. Posterior elongation is common in larger individuals. Beaks project equally, slightly, beyond hinge line. Auricles small, unequal, costate, and lirate. Byssal notch moderately deep. Hinge length less than half shell length. Right-valve ribs 14-15 or 16, ribs and spaces costate and lirate. Rib profiles narrow, rectangular, and moderately high. Left-valve ribs 14-15, with two or more elongate nodes on the central and fourth posterior ribs. The central rib and one or two others usually bear elongate hollow swellings or incipient nodes before the break in shell slope. The node scheme can be described as 3r N 2r Nc 3r N 2r. The largest individuals measured 8 cm high (TU 1071). The fact that many specimens had repaired shells suggests that the single prominent ledge may be related to injury. However, uninjured specimens from other localities are also ledged and shell growth seems to be continuous. The ledge is a normal character. Only one individual has been found with two articulated valves (hypotype UCMP 37395). Variability.— Variation among specimens from the type area is low. Specimens from Baja California Sur here referred to ''Lyropecten" sp. aff. "L." dumblei, differ in lacking the pronounced left-valve ledge and welldeveloped elongate thickenings. Individuals from northwestern Florida are scarce and poorly preserved, occurring at a few localities with "L." condylomatus', the Chipola Formation specimens have one or two fewer ribs than those from eastern Mexico. Gardner (1945) noted the early confusion between L. dumblei and L. condylomatus and the misidentification of the Mexican species as "L." condylomatus. "Lyropecten" condylomatus varies in rib count and node scheme; some specimens overlap "L." dumblei in rib count, but none have its single angular ledge and node scheme. Comparative notes.— "Lyropecten" dumblei is distinguished from "L." condylomatus in having evenly spaced ribs and a consistent left-valve node scheme, 7r Nc 3r N 3r. It has 13-15 ribs; "L." condylomatus has 10-11, a few individuals as many as 13. Disarticulated juvenile right valves of the two species are hard to distinguish. Phylogenetic affinities.— "Lyropecten" dumblei seems to be ancestral to "L." condylomatus, although records for the taxa are meager outside their respective type areas, and foraminifers from the two areas suggest that the species could be penecontemporaneous. Lyropecten sp. aff. "L." dumblei (pl. 20, figs. 9-11) occurs in the lower Miocene Isidro Formation near La Purisima, Baja California Sur, Mexico (locations USGS 9157, 9160; CAS 36409; M9165). It resembles "L." dumblei in internal hinge, size, and growth form but lacks the characteristic left-valve ledge and elongate nodes. It may also be ancestral to L. pretiosus, the oldest Pacific Lyropecten. Geographic distribution and stratigraphic occurrences.— Coastal plain of northeastern Mexico, states of Tamaulipas and Veracruz; Sinu Basin, northwestern Colombia. Florida panhandle along the Chipola River, cooccurring with "L." condylomatus. Northeastern Mexico, Guajalote Formation [San Fernando and San Rafael Formation of early workers], near San Fernando, Tamaulipas: USGS 13455, 13585, 13587, 13588; 3419; GAS 40508, 40274; 41034, 41053; UCMP S-8293 (occurs with a Chesapecten); TU 430. Veracruz, Mexico. Tuxpan Formation, Papantla region (GAS 41039, 41040; TU 1071). Planktonic foraminifers from TU 1071, which are from zones N 10 or N 11, are interpreted as indicating 30 m in depth (W.H. Akers, oral commun., 1981). Rio Las Playas (UCMP S-8219). Northern Colombia, Departamento Cordoba, Sinu River basin. Hatachica, above Maria Magdalena [= La Risa] (UCMP S-7331). Rio San Juan area, Quebrada Pajuil (USGS 1625, 1626). Uncertain occurrence, Baja California Sur, Mexico (Smith, 1984). La Purisima area (USGS 9157, 9160; GAS 36409; M9165). Northwestern Florida. Oak Grove Formation, Sand Member, Shoal River Formation (USGS 659 = 11659, very worn material). Chipola Formation (USGS 3419; 2564). Sarasota County, Fla., with "L." condylomatus at USGS 23596, 23598, South Point Drive, Hawthorn Formation. Geologic age.— Late Oligocene or early Miocene to middle Miocene.» SMITH, J. T. 1991. Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province: Lyropecten, "Macrochlamis", Vertipecten, and Nodipecten species. United States Geological Survey Professional Paper, 1391: v, 155p. , figs. 1-18, pls. 1-38. [p. 71, 72] |
"Lyropecten" dumblei (Gardner, 1945); J. T. Smith, 1991, Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province, plate 1, figures 6, 7 (above); plate 20, figures 4a, 4b, 5, 8 (below).
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