Lyropecten crassicardo (Conrad, 1856)
CONRAD, T. A. 1857. Descriptions of three new genera; twenty-three new species middle Tertiary fossils from California and one from Texas. Proceedings of the Academy of Natural Sciences of Philadelphia, 8: 312-336 [Reprinted in Dall 1909: 173-175]. [p. 313]
1856 Pallium crassicardo Conrad, 1856
1906 Pecten (Lyropecten) crassicardo var. hamiltoni Arnold, 1906
1906 Pecten (Pallium) holwayi Clark, 1915
1917 Pecten crassicardo biformatis Nomland, 1917
1922 Pecten (Lyropecten) vickeryi P. D. Trask, 1922
1922 Pecten (Lyropecten) ricei P. D. Trask, 1922
1931 Pecten crassicardo nomlandi Hertlein, 1931
1969 Swiftopecten adekunbiana Adegoke, 1969
1906 Pecten (Lyropecten) crassicardo var. hamiltoni Arnold, 1906
1906 Pecten (Pallium) holwayi Clark, 1915
1917 Pecten crassicardo biformatis Nomland, 1917
1922 Pecten (Lyropecten) vickeryi P. D. Trask, 1922
1922 Pecten (Lyropecten) ricei P. D. Trask, 1922
1931 Pecten crassicardo nomlandi Hertlein, 1931
1969 Swiftopecten adekunbiana Adegoke, 1969
Pecten (Lyropecten) crassicardo Conrad; R. Arnold, 1906, The Tertiary and Quaternary pectens of California, plate 17.
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«Obtusely ovate or suborbicular, thick; lower valve ventricose; ribs 15-16, elevated, back rounded, sides flattened, disks radiatostriate, 9 or 10 on the ribs, intervals of ribs concave, umbo or whole disk at wide intervals having a tendency to be humped and nodose; upper valve convex or slightly ventricose; ears large, equal; hinge thick, with prominent, acute, oblique teeth; fosset profound; muscular impression very large. Height 5 inches.
Locality. Monterey Co., Cal. A. S. Taylor.» TIMOTHY ABBOT CONRAD, 1857
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«Description.— Valves flat to moderately convex, left-valve profiles smooth or with one or more angular ledges producing a steplike profile in shells as much as 5 cm high (fig. 9). Beaks project equally, slightly, beyond hinge line. Auricles large, subequal, costate, lirate. Anterior auricle with five prominent radials crossed by fine imbricating lirae. Byssal notch moderately deep. Hinge line more than half shell length. Umbonal angle varies with convexity, 90°-110°. Right valves with 14-15 rectangular ribs. Left valves with 14 ribs; some specimens with prominent key ribs in the central and fourth lateral positions, as indicated by the scheme N 2r Ne 2r N. Ribs narrower, interspaces broader in left valves than in right valves. Nodes or thickenings common at ledge margins of juvenile parts of some shells (pI. 24, figs. 1, 3). Some specimens have no discernible key ribs; others three, four, or five, all separated by two normal ribs. Whether these additional key ribs appear anteriorly or posteriorly may have biostratigraphic significance, but precise stratigraphic data were lacking for much of the material available.
Fine costae and lirae on ribs and interspaces produce even, reticulate fine macrosculpture. Truly "giant pectinids," one specimen of L. crassicardo is 19.5 cm high and 20.0 cm long (CAS 503, Kimballs Wells, Coalinga). Variability.— Lyropecten crassicardo varies considerably in valve convexity, presence and number of angular ledges, and prominence of key ribs on left valves. The node scheme (N 2r Ne 2r N) and lirate, striate fine macrosculpture are consistent features. Valves may be flat and thin, as in specimens from San Clemente Island (UCR 7597, LACMIP 1194), or moderately convex. Left valves may have 0-5 angular ledges. Incipient nodes or elongate thickenings (pI. 24, fig. 3) are common on geologically younger individuals. Some large adult shells are elongated posteriorly, a growth habit with no phylogenetic significance. There is some tendency to fewer ribs on the left valve (13-14) in material from southern California compared with 14-15 ribs in Transverse Range specimens. Comparative notes.— Lyropecten crassicardo is found with L. estrellanus in many outcrops of the Santa Margarita Formation. Lyropecten crassicardo has fewer ribs, angular ledges, flat juvenile valves, radially striate, lirate fine macrosculpture, and incipient to prominent key ribs of the scheme N 2r Nc 2r N. Lyropecten estrellanus is rounded to gibbous in profile, especially in juveniles; i thas 16-17 ribs, rounded ledges, no key ribs, and a single midriblet in each interspace. Phylogenetic affinities.— Lyropecten crassicardo and the Holocene L. magnificus belong to a phylogenetic series that includes specimens from Baja California Sur referred here to Lyropecten sp. cf. L. magnificus. They are classified as a bioseries on the basis of rib counts, macrosculpture and left valves showing a progression of incipient key ribs evolving to ribs bearing hollow nodes in the scheme N 2r Ne 2r N. The highest stratigraphic occurrences of L. crassicardo tend to be specimens having 3-5 ribs with elongate thickenings (pI. 24, figs. 1, 5) in the same positions occupied by hollow nodes in Lyropectens living in the Galapagos today (pI. 24, fig. 2). Right valves lack any obvious clues to phylogeny. Lyropecten sp. cf. L. magnificus from Baja California Sur is probably ancestral to L. crassicardo, and Lyropecten pretiosus (= L. submiguelensis of authors) is either a co-occurring species or a variant of the ancestral taxon.» 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. 52, 53]
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Lyropecten crassicardo (Conrad, 1856); J. T. Smith, 1991, Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province: Lyropecten, "Macrochlamis", Vertipecten, and Nodipecten species, plate 23, figures 1, 4; plate 24, figures 1, 3-9; plate 25, figures 1-7.
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