Vertipecten bowersi (Arnold, 1906)
ARNOLD, R. 1906. The Tertiary and Quaternary pectens of California. United States Geological Survey Professional Paper, 47: 1-264, pls. 1-53. [p. 71, pl. 12, figs. 1-2; pl. 13, figs. 1, 1a]
R. Arnold, 1906, plate 12.
R. Arnold, 1906, plate 13.
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«Description.— Shell averaging about 150 millimeters in altitude and length, inequivalve, equilateral, rather thick, ventricose, and with smooth margins; base regularly rounded; sides sloping, the anterior ones slightly concave upward. Right valve considerably less ventricose than left, the surface of the disk being almost flat until an altitude of 50 or 60 millimeters is reached, when it begins to be more or less convex; surface ornamented with about 18 subequal, prominent, rounded ribs, which, with the interspaces, are obsoletely radiately striate and crossed by tine wavy incremental lines; the ribs tend to become smaller toward the sides of the disk, there being a varying number of riblets near the sides in different specimens; interspaces subequal, round bottomed, about as wide as the ribs, and sometimes containing an auxiliary riblet; hinge line about three-fifths length of shell; ears about equal in length, anterior ear divided into two nearly equal parts by a line radiating from the apex, the part above the dividing line being ornamented by 3 or 4 radiating ribs and concentric lines while the lower part (byssal area) is ornamented by imbricating incremental lines which are convex toward the apex; byssal notch wide and of medium depth; posterior ear rectangularly truncated, radiately ribbed, and crossed by concentric incremental lines. Left valve prominently and evenly ventricose; sculptured the same as the right valve except that most of the interspaces contain an auxiliary riblet; anterior ear arcuate ended, radiately ribbed, and with concentric incremental sculpture; posterior ear as in right valve.
Dimensions.— Alt. 150 mm.; long. 150 mm.; hinge line (restored) 90 mm.; diameter 55 mm. This species is distinguishable by its large size, almost smooth rounded ribs, and the greater convexity of the left valve. The flat surface of the right valve near the apex is also a very noticeable characteristic. P. bowersi is placed in the section Lyropecten because of its hinge and general aflinity to the group. It, however, lacks the radial secondary sculpture found developed to a greater or less degree on most of the species of this group, and is also different from the other members examined by the writer in having the left valve noticeably the more convex. P. bowersi ranges from the lower to possibly the middle Miocene, being found associated in some localities with P. magnolia, and in others with P. discus. The type which is figured is from Santa Inez Canyon, Santa Barbara County, and is now in the collection of the University of California. Named in honor of Dr. Stephen Bowers, of Los Angeles, one of the pioneer geologists of southern California, to whom the writer is indebted for much valuable material and information used in the preparation of this paper. RANGE
Miocene (middle?). Gillis's ranch, 10 miles southwest of Paso Robles, San Luis Obispo County (J. P. Smith).
Miocene (lower). Santa Inez Canyon, Santa Barbara County (Voy; J. H. Wilson); La Panza Creek, San Luis Obispo County (Fairbanks; R. Moran; Arnold); Barker ranch, and ''top of hill" at Long Tom mine and Miller Bros, ranch east of Annette P. O., Kern County (Watts; Arnold); 30 miles north of Santa Monica and 1 mile from ocean, Ventura County (R. E. Maynard); Santa Monica Mountains, Los Angeles and Ventura counties (Bowers). Station No. 550, Santa Ana Mountains (Watts).» RALPH ARNOLD, 1906
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«Holotype.— UCMP 12075, a large, double-valved, worn adult specimen 15.0 cm high, 14.7 cm long; hinge line (restored) 9.0 cm.
Paratype.— LSJU 432. Type locality.— Santa Inez [= Ynez] Canyon, Santa Barbara County, Calif., western Transverse Ranges, north flanks of Santa Ynez Mountains. Arnold (1906) considered it "***lower to possibly the middle Miocene;" subsequent work restricts the range to late early Miocene to early middle Miocene, upper "Vaqueros" Stage. It is not, as originally cited (Conrad, 1855b), associated with an older index fossil, Pecten magnolia. Taxonomic comment.— Two early Miocene Vertipecten species are confused by many workers because of morphologic similarity and misinformation about the type material. Vertipecten bowersi (Arnold) and V. nevadanus (Conrad) of authors form a phylogenetic series documented by gradational shell characters and stratigraphic succession. Specimens referred by authors to V. nevadanus are older than the incompletely diagnosed, poorly sketched external mold described as Pecten nevadanus by Conrad, who designated no holotype. Subsequent field work in Conrad's type area near Ocoya (now Poso) Creek has yielded a few poorly preserved fragments (USGS M1698) of the younger Miocene taxon widely known as V. bowersi (Arnold). None of this very poor material could serve as lectotype for Pecten nevadanus Conrad. In any case, it is preferable not to reinstate the name after its use for almost 75 years for another, older species of Vertipecten, referred to herein as V. kernensis (Hertlein). Vertipecten bowersi is based on a reasonably well preserved holotype from the western Transverse Ranges of southern California. Arnold (1906) noted that Conrad's brief description and drawing of a right valve closely matched his own Pecten bowersi with respect to shell size, byssal area, and ribbing, although he hesitated to synonymize his taxon on the basis of few specific characters. Later workers thought Conrad's Pecten nevadanus was the same as the abundant, well-preserved pectinid [V. kernensis (Hertlein) of this report] from Pyramid Hill, about 4 mi southeast of the type Ocoya Creek area (Ml698). Regional mapping and biostratigraphic studies by Addicott (1970) and Bartow and Doukas (1976) established significant chronostratigraphic differences between the Freeman Silt-Jewett Sand sequence at Pyramid Hill and the younger Olcese Sand that crops out to the southeast, west, and northwest. Disarticulated right valves or poorly preserved material of the two Vertipecten species from these units are hard to separate. Grant and Gale synonymized Pecten bowersi and P. nevadanus, designating the type of Vertipecten as "Pecten nevadanus Conrad (+ Pecten bowersi Arnold)." The present study differentiates two species based on rib count, fine macrosculpture, and left-valve rib patterns. In the currently accepted geochronologic scheme, V. bowersi is a late early Miocene index species of the upper "Vaqueros" Stage; V. kernensis (= V. nevadanus auctt.) is latest Oligocene to early Miocene, indicative of the middle "Vaqueros" Stage. The stratigraphic ranges of Vertipectens from California and the Pacific Northwest are shown in figure 12. Description.— Right valves flat, left valves highly convex; height equal to or slightly greater than length. Beaks meet at hinge line. Auricles equal, radially ribbed; byssal notch deep; umbonal angle about 95º. Adult right valves with 15-16 rounded-rectangular ribs (15-17 in juveniles); left valves with 14-15 rounded, narrow rectangular ribs, higher than those on right valves. Several prominent key ribs on left valves, including the central rib and anterior and posterior laterals separated from it by two lesser ribs. Fine macrosculpture of concentric growth lines and a single midriblet in each interspace. Small flanges rarely preserved on lateral ribs or over whole shell. Specimens rarely show the shagreen microsculpture5 that is present in interspaces on both valves of UCSB hypotype M17 ( = UCSB 1806, from Santa Cruz Island). Adults measure more than 20 cm high, 22 cm long (UCR 7232, from Saddle Peak, Santa Monica Mountains). One shell measured 0.9-1 cm thick at its margin. Morphologic variability.— Valve profiles vary between juvenile and adult stages, from flat to slightly convex in most individuals. Very large specimens, including many examples from the Caliente Range (USGS loc. M3439), become swollen in outline (fig. 9). Right-valve rib width and spacing variable, as in V. kernensis (= V. nevadanus auctt.), V. fucanus, and V. perrini. Anterior and posterior parts of the shell may have narrow, incipient riblets which complicate the rib count. Left-valve key ribs may number one (in the central position), two (central and anterior) or three, of which the posterior rib may be less prominent than the others. Comparative morphology.— Vertipecten bowersi commonly occurs with Lyropecten miguelensis, another giant pectinid index species of the lower Miocene upper "Vaqueros" Stage. Lyropecten miguelensis is distinguished by a typical Lyropecten hinge having two pairs of crura in the left valve, three pairs on the right valve, and by radial ribs sculptured with radial lines and concentric lirae. Valve profiles both convex in L. miguelensis, one planar and one convex in V. bowersi. Byssal notch in Vertipecten is deeper, more set off than in Lyropecten. Vertipecten kernensis has more ribs, scalier fine sculpture, and more equal valve proportions than the younger species of Vertipecten. Vertipecten fucanus has flattopped, rectangular ribs, a single key rib with imbrications on left valves, and shagreen microsculpture rather than a well-defined midriblet in each interspace. Phylogenetic affinities.— Overlapping morphologic characters and stratigraphic succession document the phylogenetic series V. yneziana-V. perrini-V. kernensis (= V. nevadanus auctt.)-V. bowersi. All are known only from California south of the Mount Hamilton Range; geographic distributions are wider for V. bowersi. Vertipecten bowersi and V. kernensis are possible ancestors to V. fucanus, although the latter species is common in the lower Miocene of Washington and Oregon and may represent a separate lineage. Morphologic evidence of phylogenetic relations is marked in left valves, more obscure in right valves. Geographic distribution and stratigraphic occurrences.— Central and southern California, from the northern La Panza Range, Caliente Range, Transverse Ranges and Santa Cruz Island; Orange County. East of the San Andreas fault in the northern Temblor Range and in canyons north of Poso Creek, Kern County. Erroneously reported from Vaqueros Creek, Monterey County (Loel and Corey, 1932, p. 198). Representative stratigraphic occurrences.— Vaqueros Formation, sandstone member: La Panza 7½-minute quadrangle (M4670; CAS 53; found with L. miguelensis); southwest Santa Cruz Island (UCSB 1806 = M17); found with L. miguelensis in a fine-grained sandstone that interfingers with the upper part of the coarse diorite breccia member (McLean and others, 1976). Vaqueros Formation, Painted Rock Sandstone Member: Caliente Range, Carrizo Plain area (M5199, west of Soda Lake, Chimineas 7½-minute quadrangle, Vaqueros Formation, Painted Rock Sandstone Member: central Sierra Madre Range (Fritsche, 1969), at UCLA 5554, and with L. miguelensis at UCLA 5548, 5549, CSUN 91. Temblor Formation, Carneros Sandstone Member: northern Temblor Range (M2633 = USGS 4941, Packwood Creek 7½-minute quadrangle; very large specimens more than 20 cm high found with L. miguelensis). Monterey Formation, Saltos Shale Member: Caliente Range, Sierra Madre and San Rafael Mountains, and Cuyama Valley (abundant specimens of V. bowersi and L. miguelensis throughout the Saltos Shale Member at M3430, M3448, M3771, M3320). Abundant V. bowersi at M3446, M3436 (basal part of Saltos Shale Member), M3439, M2416. Technically deformed specimens from M2418, just below contact with the overlying Branch Canyon Sandstone; San Rafael Mountains, UCR 1285, calcareous sandstones between Zaca and Corral Canyons. Santa Monica Mountains; Calabasas, Point Dume, and Malibu Beach 7½-minute quadrangles (Yerkes and Campbell, 1980a,b), in the Topanga Group and the undivided Vaqueros Formation and Topanga Group: M4027, very thick shelled specimens in sedimentary breccia of upper part of the Topanga Group; UCR 7232, a large individual from upper Las Flores Canyon, possibly a link between V. kernensis and V. bowersi. Topanga Canyon Formation, Saddle Peak Member: M1953; M4018; CSUN 24; SGS, 1910 localities. Ten cm thick basal conglomerate bed with abundant V. bowersi [identified as V. nevadanus by authors] can be traced along southwest shoulder of Saddle Peak, Malibu Beach 7V2-minute quadrangle in T. 1 S., R. 17 W. (Yerkes and Campbell, 1980a,b). Unit is denoted by the symbol Tn2, below the Conejo Volcanics, in preliminary maps of Campbell and others (1970). Vaqueros Formation, San Nicholas Member: Triumpho Pass 7½-minute quadrangle; very poorly preserved specimens, some external molds. Santa Ana Mountains (fide Arnold, 1906; Dickerson, 1914). Elesor Creek, 2.5 miles southeast of El Toro (USGS 4132). Very large specimens from the Vaqueros Formation in Laguna Canyon, Orange County, (UCMP A-527), and west of Laguna Canyon in the Topanga Formation (J.G. Vedder, written commun., 1983). Poso (formerly Ocoya) Creek area, Knob Hill 7½-minute quadrangle, Olcese Sand: USGS 6627, poorly preserved fragment from concretionary sands that Addicott regards as lower part of the Olcese Sand (material is transitional between V. kernensis and V. bowersi). Geologic age.— Early Miocene. Biostratigraphic range.— Upper "Vaqueros" Stage. Loel and Corey (1932) noted its "***wide distribution in the Vaqueros horizon," which they considered early Miocene, and in what they called the middle Miocene Temblor Formation. Vedder and others (1973) reported that the species [identified as V. nevadanus] ranges into lowest Relizian in the Caliente Range. After several shifts in age-stage correlations, the taxon is currently considered early Miocene in age. Paleoecology.— The species is most abundant in nearshore clastic facies. Specimens can be seen at Point Mugu in random orientations in a turbidite deposit.» 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. 78, 79]
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Vertipecten bowersi
(Arnold, 1906); J. T. Smith, 1991, Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province, plate 32, figures 4, 5 (above; plate 35, figures 2-4 (below). |
«This large and variable species, sometimes difiicult of recognition in poor material, has a wide distribution in the Vaqueros horizon. It is distinguishable from P. perrni Arnold (1906) by its fewer and more rounded ribs, and the usual convexity and similarity of both valves—unlike P. perrini.
Geologic range.— Vaqueros horizon, Lower Miocene, and Temblor, Middle Miocene. Distribution in Vaqueros.— Western Santa Monica Mountains, Ventura and Los Angeles counties; Santa Ynez River Canyon, Santa Barbara County; Santa Maria region, San Luis Obispo County; Vaqueros Creek, Monterey County. Reported from Santa Ana Mountains by Watts and by Dickerson (1914).» LOEL, W. & W. H. COREY. 1932. The Vaqueros formation, lower Miocene of California I. Paleontology. University of California Publications, Bulletin of the Department of Geological Sciences, 22 (3): 31-410, pls. 4-65. [p. 198]
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Pecten (Lyropecten) bowersi Arnold; W. Loel & W. H. Corey, 1932, The Vaqueros formation, lower Miocene of California I. Paleontology, plate 22, figure 1.
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