"Macrochlamis" magnolia magnolia (Conrad, 1857)
CONRAD, T. A. 1857. Report on the paleontology of the Survey [Parque's Survey]. In: Reports of explorations and surveys railroad from the Mississippi River to the Pacific Ocean. Senate Executive Document, 78 and House of Representatives Executive Document, 91, vol.7: 189-196, pls. 1-10 (Reprinted in Dall 1909: 180-185). [p. 191, pl. 1, fig. 2]
1857 Pecten magnolia Conrad, 1857
T. A. Conrad, 1857, plate 1.
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«PECTEN MAGNOLIA, pl. 1, fig. 2.— Suborbicular, ribs 11, very large, prominent, convex-depressed on the back, laterally angulated, longitudinally rugoso-striate.
Locality.— Santa Inez mountains, Santa Barbara county, California. This species will compare in size with P. Jeffersonius, Say, and is so remarkably similar to it that it may prove to be the same species when more perfect specimens are collected.» TIMOTHY ABBOT CONRAD, 1857
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«Taxonomic comments.-- Pecten magnolia Conrad has long been classified as a Lyropecten because of its interior hinge crura, large size, and morphologic similarity to a large number of species referred to that genus. Addicott (1972) noted that the shell proportions and giant size of auricles resemble those of European pectinids of the Macrochlamis latissimus-M. holgeri group; he considered P. magnolia the first representative of that stock in western North America. The genus is unknown in the Eastern United States, but it ranged widely during Miocene and Pliocene time in the eastern and western Tethys of Europe.
Two subspecies are recognized here: the 9-10 ribbed "M." magnolia, s.s. and a fewer ribbed form, "M." magnolia ojaiensis, n. subsp. They are separable biostratigraphically, the former occurring in the lower lower "Vaqueros" Stage, the latter in the upper lower "Vaqueros" to lower middle "Vaqueros" Stage. Ranges of "M." magnolia, s.s. and "M." magnolia ojaiensis overlap those of Vertipecten perrini and V. kernensis, respectively. Gradational specimens occur in upper Oligocene rocks of the Santa Cruz Mountains, the Santa Ynez Range, the Nipomo-Huasna basin, and the western Santa Susana Mountains (fig. 11). Neotype.— UCMP 31729, here selected, illustrated by Loel and Corey (1932, pI. 27, fig. 2).
Conrad designated no holotype, although the original description mentioned 11 ribs and very large size. His illustration does not match his description; it seems to be a valve of Pecten meekii Conrad. Arnold (1906) referred to type specimens at the U.S. National Museum (USNM 13311 and 13325), but they are fragments of L. crassicardo and not Conrad types. Type locality.— Santa Ynez ("Inez") Mountains, Santa Barbara County, Calif. Subsequent field work suggests it is on the north side of the range and in the Santa Ynez Valley, probably in the vicinity of the San Julian Ranch (Lompoc 15-minute quadrangle), in T. 5 N., R. 30 W. (Keen and Bentson, 1944). Neotype locality: about 0.5 mi north of Jalama Creek, near Escondido Creek, Santa Ynez Mountains (loc. UCMP A-315). Oligocene, Vaqueros Formation, basal part (Loel and Corey, 1932, p. 91). Significant hypotype.— UCMP 37387 (loc. UCMP D-8794). Description.— Valves massive, subcircular; juvenile right valves more convex, left valves flat. Right-valve beak projects farther beyond hinge line than left beak (pI. 31, fig. 1). Auricles very large, sculptured by fine growth lines, a few faint radials near the hinge. Posterior auricle higher than anterior. Byssal notch weak. Hinge has three pairs of strong cardinal crura; hinge length about half shell length. Right-valve ribs 9-10, wider than interspaces. Fine macrosculpture obsolete, mainly concentric growth lines. Left-valve ribs 9-10, narrower than interspaces. The fine sculpture, rarely preserved, consists of several fine radial striae crossed by concentric growth lines (hypotype UCMP 37387, pI. 31, fig. 5). Many large specimens from Cuyama Valley (for example, locality M3519) are extremely swollen. One giant measured 25 cm high, 28-30 cm long, 14.5 cm in hinge length (J.G. Vedder, oral commun., 1973). Variability.— Juveniles have 10 high, narrow ribs, adults 8-9 lower rectangular ribs, lateral riblets becoming incipient in some cases. Loel and Corey (1932) noted rib counts of 10-12 in many specimens, as low as 6 in others. Stratigraphic and geographic data support the subdivision into two subspecies differentiated by rib count. Within each subspecies, ribs vary by one or two. Comparative notes.— Subspecific differences are as follows:
Phylogenetic affinities.— Biostratigraphic data indicate that the many ribbed "M." magnolia s.s. is the older subspecies and direct ancestor of "M." magnolia ojaiensis. There is no other representative of "Macrochlamis" in North America; a comprehensive systematic revision of European pectinid genera may indicate that "M." magnolia, s.l. and the close European cognate identified here as M. terebratulaeformis belong in another genus. Arnold (1906) considered Pecten magnolia ancestral to L. crassicardo, but that lineage is not borne out by the morphologic progression and fossil record of Lyropecten sp. cf. L. magnificus and L. pretiosus (including L. submiguelensis auctt.)-L. crassicardo-L. magnificus. The phylogenetic relation, if any, between "Macrochlamis" and Lyropecten is unknown.»
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. 73]
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"Macrochlamis" magnolia magnolia (Conrad, 1857); J. T. Smith, 1991, Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province: Lyropecten, "Macrochlamis", Vertipecten, and Nodipecten species, plate 29, figures 3, 4; plate 31, figures 1, 5; plate 37, figures 2, 4.
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«Original description: "Suborbicular, ribs 11, very large, prominent, convex-depressed on the back, latelally angulated, longitudinally rugoso-striate. Loeality, Santa Ynez Mountains, S. B. C."
In one zone of the type region in the western Santa Ynez Mountains, Pecten magnolia Conrad has developed 10 to 12 ribs in a large percentage of individuals. A count of all specimens in the collections and in the field gives an average rib number of 9 and a range of 6 to 13. The umbone of the right valve is commonly higher and more convex than that of the left, projecting above the hinge line. Geologic range.— Pecten magnolia Conrad is confined to the Vaqueros horizon, Lower Miocene, with geographic distribution from San Joaquin Hills, Orange County to Mindego Hill and Corte Madera Creek, San Mateo County, being found nearly everywhere that Vaqueros beds are present, including Kern River district, Kern County. By reason of the wide distribution, abundance, and distinct form of Pecten magnolia Conrad, it is considered one of the most characterlstic molluscs of the Vaqueros horizon. Pecten magnolia Conrad is probably derived from the stock of Pecten jeffersonius Say of the Maryland Miocene (Dall, 1903a). Frequent individuals show much resemblance in many characters. Pecten crassicardo Conrad (1855, 1856, 1857) is perhaps the nearest related West Coast Tertiary species, some individuals having as few as 13 and 14 ribs of the same character, while in one zone in the western Santa Ynez Mountains a large percentage of the individuals of Pecten magnolia Conrad have as many as 11 and 12, ribs. Two individuals were found here with 13 strong ribs. Pecten miguelensis Arnold is also closely related and possibly derived from the Pecten magnolia Conrad form, as in some localities the former has none or but very faint intercalary ribs.» 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, 199]
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Pecten (Lyropecten) magnolia Conmd; W. Loel & W. H. Corey, 1932, The Vaqueros formation, lower Miocene of California I. Paleontology, plate 27, figures 1, 2. [figure 1 non Pecten magnolia Conrad, 1875: "Macrochlamis" magnolia ojailensis Smith 1991; fide J. T. Smith 1991, p. 74]
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