Vertipecten alexclarki Addicott, 1973
ADDICOTT, W. O. 1973. Oligocene molluscan biostratigraphy and paleontology of the lower part of the Type Temblor Formation, California. United States Geological Survey Professional Paper, 791: 1-48, pls. 1-9. [p. 26, pl. 1, figs. 9, 10, 13; pl. 2, figs. 1, 3, 5, 8, 9; pl. 3, figs. 1, 4]
1906 Pecten (Chlamys) branneri Arnold, 1906 [partim]
1973 Vertipecten alexclarki Addicott, 1973
1973 Vertipecten alexclarki Addicott, 1973
W. O. Addicott, 1973, plates 1-3.
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«1905. Pecten sp. Anderson, California Acad. Sci. Proc., 3d ser., v. 2, no. 2, p. 170.
1906. Pecten (Chlamys) branneri Arnold, U.S. Geol. Survey Prof. Paper 47, p. 55-56 (in part), [not pl. 3, figs. 9-11]. 1972. Vertipecten n. sp. Addicott, Soc. Econ. Paleontologists and Mineralogists, Pacific Sec., Bakersfield, Calif., 1972, Proc., pl. 1, figs. 16, 18. Moderately large, reaching as much as 115 mm in height, higher than long. Apical angle narrow, averaging about 70º. Right valve relatively flat; has 20 to 30 or more flat-topped, scaly ribs that tend to be dichotomous in the central portion of the disk but more irregular in development toward the sides. Scales are fine and closely spaced near beak but become coarser and more widely spaced toward base. Secondary riblets usually developed in the interspaces between the paired ribs. Anterior auricle long, set off by deep byssal notch. Auricle sculptured by five strong ribs bearing heavy flanges. Left valve convex and has rather uniform sculpture of primary, secondary, and tertiary rounded ribs bearing strong, rather widely spaced flanges toward the base. Medial primary and two lateral primaries that tend to divide the disk into quadrants are somewhat stronger than other primary ribs.
This species is assigned to Vertipecten because of the distinct inequality of the valves, the right valve being relatively flat and the left being moderately convex (pl. 1, fig. 10), and because of the relatively greater strength of the central and two lateral primary ribs on the left valve, the three of which tend to divide the valve into quadrants. In sculptural detail and in the size of the right anterior ear, the species resembles Chlamys. The right valve of Vertipecten alexclarki n. sp. is characterized by narrow, flat-topped ribs that are highly irregular in their development, whereas the left valve has a more or less orderly development of rounded primary, secondary, and tertiary ribs. The ribs of both valves are scaly. This species seems to be a lineal antecedent of the early and middle Miocene species Vertipecten perrini (Arnold). The Miocene specifies differs, however, by having fewer, much coarser ribs on the right valve that also tend to be smooth and generally are not dichotomous. The medial portion of the right valve of V. perrini also has a depression coinciding with an interspace and reflecting a relatively much more strongly raised medial rib on the left valve. The sculpture of the right valve of Chlamys branneri (Arnold, 1906, p. 55-56, pl. 3, figs. 9-11), a middle Miocene species from the eastern foothills of the Santa Cruz Mountains, is similar to that of the Vertipecten alexclarki. In fact, some workers (Kleinpell, 1938; Stinemeyer and others, 1959; Foss and Blaisdell, 1968) identified C. branneri from the Wygal Sandstone Member. Although the type material of C. branneri is poorly preserved, it is an equivalved species and, therefore, is properly assigned to Chlamys and not to the subsequently proposed genus Vertipecten, which is characterized by a relatively flat right valve and a convex left valve (see pl. 1, fig. 10). Other differences are the similar sculpture of both valves of C. branneri, the lack of an accentuated medial rib on the left valve, and the greater number of radial ribs on the auricles of that species 6 to 10 rather than 5. It is possible that a specimen, or specimens, identified by Arnold (1906, p. 56) as C. branneri from the lower part of what is now mapped as Vaqueros Sandstone (Brabb, 1964) on Twobar Creek in the Santa Cruz Mountains, may represent V. alexclarki n. sp. The material is from rocks of approximately the same age. C. branneri, on the other hand, is from unnamed rocks of middle Miocene age from Coyote Hills near the Stanford University campus (Dibble, 1966). This species is named for Alex Clark, who made extensive unpublished studies of Oligocene and Miocene mollusks of the southern part of the San Joaquin basin for Shell Oil Co. during the 1930's (1931-1935, Department of Geology, California University, Riverside). Localities. — USGS 5149?, M3280, M3281, M3579, M3636, M3772, M3984, M3985, M4466, M4468, M4470, M4472.» WARREN OLIVER ADDICOTT, 1973
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«Lectotype.— USNM. 646531, a right valve, height 6.9 cm, length 6.6 cm (subsequent designation, Moore (1984b).
Type locality.— Central Temblor Range, Kern County, Calif. Las Yeguas Ranch 7V2-minute quadrangle, on south side of hill 2259 just below summit; 2,200 feet north, 1,000 ft west of southeast corner sec. 22, T. 28 S., R. 19 E. (USGS M3281). Temblor Formation, base of the Wygal Sandstone Member (Addicott, 1973) [= Phacoides sand of local usage; see Stinemeyer and others, 1959] late early or middle Oligocene in age. Paratypes.— USNM 646538, 646539. Hypotypes.— USNM. 646528, 646529, 646530, 646532 CAS 60862. Description.— Right valve flat, left valve convex, nearly equal; height exceeds length. Beaks do not project above hinge line. Right auricle square, with 4-5 radials; no complete left auricles seen. Byssal notch deep. Umbonal angle narrow, about 70°. Ribs 24-34, hard to count because they are narrow, sometimes split, and barely distinguishable from interriblets; left-valve ribs of several sizes, as in V. perrini and V. kernensis (= V. nevadanus auctt.), but with no single key rib. Fine sculpture consists of many fine radial ribs and interspace riblets with very fine imbrications. Adults small compared to other Vertipectens, the largest measuring 11.5 cm. Morphologic variability seems low, although there are no complete individuals known and only a dozen or two fragmental specimens have been collected. Comparative notes.— Vertipecten alexclarki is typical of the oldest Vertipectens in having small, nearly equally convex valves and numerous scaly ribs of several strengths. It has the narrowest umbonal angle of any Vertipecten. Vertipecten yneziana is more circular in outline, with flatter valves and coarser ribs. Vertipecten perrini has many coarser ribs, a convex left valve and wide umbonal angle. Addicott (1973) compared V. alexclarki to Chlamys branneri (Arnold, 1906); he found the latter equivalved with auricles having 6 to 10 radials. Fine macro sculpture is similar. Vertipecten alexclarki is early to early middle Oligocene in age; C. branneri is middle Miocene. Phylogenetic affinities.— Vertipecten alexclarki is isolated geographically from the phylogenetic series V. yneziana-V. perrini, although its chronostratigraphic range falls within the transition zone between them. Its relationship to contemporaneous Vertipectens is uncertain. Geographic distribution and stratigraphic occurrences.— Central Temblor Range, between Media Agua Creek, Las Yeguas Ranch 7½-minute quadrangle and outcrops between Zemorra Creek and Temblor Creek, Carneros Rocks 7½-minute quadrangle, (T. 28-29 S., R. 19-20 E.). Wygal Sandstone Member, Temblor Formation (USGS M3280, M3281, M3579, M3636, M3772, M3984, M3985, M4466, M4468, M4470, M4472; GAS 27625). Santa Cruz Mountains: Twobar Creek, Big Basin 7½-minute quadrangle, Vaqueros Sandstone at the type locality of Pecten sanctaecruzensis (Ralph Arnold field loc. 111, LSJU accession no. 4902). The distribution in the central Temblor Range and the La Honda block of the Santa Cruz Mountains (fig. 11) supports the figure of about 300 km of post-Eocene right-slip motion along the San Andreas fault in central California (Graham and others, 1986). Reported from Junipero Serra Peak, Santa Cruz Mountains, but specimens were not seen. Geologic age.— Early to early middle Oligocene. Biostratigraphy.— Vertipecten alexclarki is restricted to the unnamed molluscan stage between the lower "Vaqueros" and upper "Refugian" Stages (Addicott, 1973). The unnamed stage is equivalent to the lower (but not lowest) part of the Zemorrian Stage at its type section in the Zemorra Creek-Chico Martinez Creek area. Paleoecology.— The Wygal Sandstone Member contains mollusks indicating shallow water to 20 fathoms, inner sublittoral conditions. The genera suggest warm temperate to subtropical temperatures; Addicott (1973) noted the occurrence of the unique eastern Pacific hermatypic coral Favosites at the type locality of V. alexclarki (M3280).» 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 + 1-155, figs. 1-18, pls. 1-38. [p. 77]
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Vertipecten alexclarki
Addicott, 1973; J. T. Smith, 1991, Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province, plate 38, figures 1-4. |