Patinopecten propatulus (Conrad, 1849)
CONRAD, T. A. 1849. Fossils from Northwestern America. 4. Mollusca. In: United States Exploring Expedition during the years 1838, 1939, 1840, 1841, 1842 (…). Vol. X. Geology. Appendix I, 4. Mollusca, pp. 723-730. Philadelphia. [p. 726, pl. 18, figs. 13, 13a]
1849 Pecten propatulus Conrad, 1849
«This large scallop shell is the most common pectinid in the Astoria Formation. Others less common are described in my earlier paper (Moore, 1963, p. 65-69). The valves are equally and slightly inflated, and each bears about 15 to 22 ribs, flat-topped on the right valve and rounded on the left valve.
Different species of Patinopecten and other pectinid genera are very useful in discriminating fossil time. A monograph by Ralph Arnold (1906) illustrates the many different kinds of pectens. For example, Patinopecten propatulus is restricted to the Astoria Formation of early to middle Miocene age and its correlatives in Oregon, whereas Vertipecten fucanus is restricted to the Nye Mudstone of early Miocene age and its correlatives (Moore and Addicott, 1987). Young individuals of all pectinid species that have light-weight shells can propel themselves efficiently by opening the valves to take in water, then closing them abruptly to squirt the water out. Patinopecten hops rather than swims as it moves in small spurts to get away from predators such as starfish. From the presumably related living species Patinopecten caurinus (Gould), we assume that this fossil Patinopecten lived at a depth of 30 m (90 feet) in small depressions on the sediment surface. Scallops, the seafood delicacy, are the muscles that hold the shells of pectinids together and closed. The small scallops commonly come from bay pectinids, whereas the larger scallops are obtained from pectinids from the nearshore ocean. The scar where this muscle was attached can be seen on fossil shells cleaned of sediment.» MOORE, E. J. 2000. Fossil shells from Western Oregon. A guide to identification. Chimtimini Press. Corvallis, Oregon. [p. 85, 86]
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Patinopecten propatulus
(Conrad); E. J. Moore, 2000, Fossil shells from Western Oregon, figure page 85. |
«Patinopecten propatulus is of moderate size and the valves are slightly and equally inflated. There are 16 to 22 flat-topped to slightly rounded or flattened finely striated ribs on the right valves and 15 to 18 evenly rounded or ridgelike ribs on the left valves. The right anterior ear has a moderately deep byssal sinus and the surface of the ear above the sinus is ribbed; the right posterior and left valve ears are finely ribbed. The right and left anterior ears are folded. Well-preserved left valves show the surface to be sculptured by an imbricated lamellar microsculpture (pl. 16, fig. 2); this sculpture may also be present on the left valve ears; it has not been found on right valves.
Type: USNM 3504 is herewith designated the lectotype, pI. 16, figs. 1, 4. This is probably the specimen figured by Conrad (1849, pI. 18, fig. 13). The lectotype has been previously figured by Grant and Gale (1931, pl. 22, fig. 5) and Weaver (1942, pI. 20, fig. 2).
Paratypes: USNM 3568. Type locality: Astoria, Oreg. The lectotype is an internal mold of both valves and only fragments of the innermost shell layer remain. The specimen was contained in a concretion and apparently only the right valve was exposed when Conrad described the species; the specimen was removed from the concretion at some later date, and both valves are now exposed. There are 16 flat-topped to slightly rounded ribs on the right valve and the interspaces are flat to slightly rounded and wider than the ribs. The left valve has probably more than 13 rounded ribs and the interspaces are slightly rounded and wider than the ribs. The lectotype is approximately 10.3 cm high and 10.2 cm wide (broken along margins).
The number and configuration of the ribs and interspaces on both valves of Patinopecten propatulus is variable. The right valve has 16 to 22 ribs; 19 ribs are most common. The interspaces may be narrow, less than a third the width of the rib, or more commonly as wide or somewhat wider than the rib. Both the ribs and the interspaces are usually flat, but they may be slightly rounded. The ribs are often square but may be moderately undercut, and show fine radial striations on well-preserved specimens. There is occasIonally an interrib in some of the interspaces especially near the anterior and posterior margins of the shell. There may also be as many as five threadlike ribs on the anterior or posterior margin of the shell; these fine ribs were not included in the rib counts. The anterior ear on the right valve has a moderately deep byssal sinus covering more than a third of the total area of the ear and 3 to perhaps more than 5 imbricated ribs on the upper part of the ear. The posterior right ear has 5 to 10 ribs usually about half as wide as those on the anterior ear. These ribs may be of equal width and may alternate with very fine threadlike ribs. The left valve has 15 to 18 ribs which are usually evenly rounded, but which may rise abruptly to a narrow ridge or may be flat-topped. Both types of ribs may be present on the same specimen. The interspaces may be flat, slightly rounded, or moderately round and may contain a fine interrib. The interribs when present are usually centered in the interspace but may be crowded close to the posterior side of the rib. Flangelike lamellae are present near the dorsal end of the first few posterior ribs on two left valves (loc. 104), plate 17, figure 4. The left anterior ear has 5 to 8 or more ribs, similar in size to those on the posterior ear of the right valve, and it usually has fine threadlike interribs. On all but immature specimens, the posterior ear is depressed medially. The left posterior ear is sculptured by 6 to 8 ribs, similar in weight to those on the anterior ear but without the fine interribs that are often present on the anterior ear. An imbricated lammelar microsculpture may be present on the left valve of P. propatulus and is fairly well preserved on one specimen (pl. 16, fig. 2). This microsculpture is on a thin now chalky shell layer that flakes off leaving no trace of the presence of the microsculpture and the remaining shell seems to be perfectly preserved. This microsculpture is described under the generic heading (p. 63). Poorly preserved specimens of P. propatulus, or specimens of only the right valve, are difficult to separate from Vertipecten fucanus (Dall). The shell of P. propatulus is usually thinner; the ribs on the right valve are often flatter; and the byssal sinus somewhat more shallow. Ribs on the right valve of V. fucanus may be split, whereas they commonly are not on P. propatulus and may be more conspicuous, narrower, and more closely and irregularly spaced; and in some specimens unevenly split, with one part half the width of the other. Because of variations in the ribs on both P. propatulus and V. fucanus, it has not always been possible to separate incomplete specimens of the two forms beyond any possible doubt. The specimen in the original type lot of P. propatulus figured by Arnold (1906a, pI. 9, figs. 1, 1a, 2, 2a) and Dall (1909, pI. 15, figs. 1, 1a, 2, 2a) as a cotype, but questioned as being conspecfic by Grant and Gale (1931, p. 192), is assigned to Vertipecten fucanus (Dall) (p. 66). P. propatulus is allied to P. caurinus (Gould) of the Recent, which has been collected from sedimentary Rocks as old as Pliocene and possibly Miocene in age. Recent specimens of P. caurinus reach a much larger maximum size than P. propatulus. The ribs on the right valve of P. caurinus tend to disappear near the margins on large specimens, and the ribs on both ears of the right valve are poorly developed, being barely discernible on some specimens. The ribs on the left valves of P. caurinus are usually flat topped whereas on P. propatulus this is rare, although they may be rounded similar to those of P. propatulus. The ribs on the left valve also tend to disappear along the margins of large specimens of P. caurinus. The ribs on the ears of the left valve of P. caurinus tend to be finer than those on P. propatulus. Interribs are less frequently present on both the right and the left valves of P. caurinus. The umbonal angle on P. propatulus is narrower than on P. caurinus, P. propatulus averaging about 100° and P. caurinus averaging about 125°. P. propatulus is common in the Astoria formation and is particularly abundant in the rocks exposed in the Johnson Creek area, just south of Otter Rock, and in the 6 feet of siltstone 1½ feet beneath the lower barren marker in the rocks intermittently exposed south of Spencer Creek to south of Schooner Creek (pI. 33). Howe (1922, unpublished, p. 85) collected this species from Fifth and Commercial Streets in Astoria and from concretions in the "Astoria shale." He also recorded P. propatulus from the Miocene of Contra Costa County, Calif. The abundance of Patinopecten is not always indicated by the number of specimens in the collections; the thinness of the shell in relation to its overall size makes it difficult to collect. Localities: 1, 1a, 3, 4, 22, 32, 37, 56, 59, 60, 61, 66, 67, 71, 79, 82-84, 89, 94, 99-101, 102a, 103-108, 112, 119, 123, 134, 135, 137, 139, 140, 144, 149, 156, 158, 181.
Occurrence elsewhere: Astoria (?) formation, Washington; Temblor formation, lower and middle Miocene, California.» MOORE, E. J. 1963. Miocene Marine Mollusks from the Astoria Formation in Oregon. United States Geological Survey Professional Paper, 419: 1-109, pls. 1-32. [p. 64, 65]
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Patinopecten propatulus (Conrad); E. J. Moore, 1963, Miocene Marine Mollusks from the Astoria Formation in Oregon, plate 16, figures 1-4; plate 17, figures 2-5, 7.
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«Miocene of the Astoria group, Astoria, Oreg., J. D. Dana; Clallam Bay, Fuca Strait, Washington, Arnold; Newport, Yaquina Bay, Oregon, Hill; Port Simpson, British Columbia, in California Acad. Sci., fide Arnold; Griswolds, San Benito County, Cal., Turner and Cooper.
This species has been confounded with the recent P. caurinus Gould, by Carpenter and others, but is sufficiently distinguished by its smaller size and more convex valves, and by having only 15 primary radial ribs.» DALL, W. H. 1909. Contributions to the Tertiary paleontology of the Pacific coast. I. The Miocene of Astoria and Coos Bay, Oregon. United States Geological Survey Professional Paper, 59: 1-216, pls. 1-23. [p. 112]
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Pecten (Patinopecten) propatulus Conrad; W. H. Dall, 1909, The Miocene of Astoria and
Coos Bay, plate 15, figures 1, 2.
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