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Journal of Paleontology 91(6):1148–1165
radial ribs covered with nodes. Nodes and paracostal ribs sup- pressed in advanced members of the genus (modified from Heaslip, 1968, p. 98).
Remarks.—The genus Claibornicardia was erected by Stenzel and Krause in Stenzel and Krause, 1957 to include few carditids from the middle Eocene of the GCP geological province (C. alticostata [Conrad, 1833], C. complexicostata [Meyer and Aldrich, 1886], C. nasuta [Dall, 1890], C. sillimani [Lea, 1833], and C. trapaquara [Harris, 1895]) and C. acuticostata (Lamarck, 1806) from the Eocene of the Paris Basin (France). According to Stenzel and Krause (1957), the key characters of the genus are the elongate-rectangular outline with a faint posterior area, and the development of tripartite radial ribs. Heaslip (1968) reviewed the genus, and extended its
stratigraphic range in the southeasternregionofthe USAfromthe early Eocene to the middle Oligocene with the addition of several new species (C. blandingi [Conrad, 1830]; C. coloradonis [Harris, 1919]; C. linguinodifera Heaslip, 1968; C. natchitoches [Harris, 1919]; C. perantiqua [Conrad, 1865]; and C. trapaquaroides Heaslip, 1968), and synonymized C. sillimani with C. alticostata, stating that it is a case of sexual dimorphism. All American species are characterized by variable outlines, with diverse degrees of elongation and posterior margin acumination (C. nasuta, C. trapaquara,and C. trapaquaroides) and/or ventral margin acumination (C. blandingi,C. complexicostata,andC. perantiqua). Particularly, C. alticostata shows strong morphological variation (as shown byHeaslip, 1968, pl. 26, figs. 6–11). Cases of allometric growth are recognized within carditids (Stanley, 1972), where the shell outlines can vary throughout ontogeny. Combining allometry with sexual dimorphism and the wide geographical distribution of certain species (e.g., C. alticostata), it is possible that the true intraspecific variation of Claibornicardia is misunderstood and some proposed American species are part of the variation of other species. Moore (1992) included within Claibornicardia four species
fromCalifornia and Baja California:C. keenae (Verastegui, 1953) (late Paleocene), C. domenginica (Vokes, 1939), C. marksi (Verastegui, 1953), and C. sandiegoensis (Hanna, 1927), the last three all being Eocene. These taxa have less elongate outlines and more convex shells than the eastern American species, but have the characteristic tripartite radial ornamentation. Claibornicardia aalterensis Vervoenen and van Nieulande,
2010, C. asperrima (Wood, 1861), C. carinata (Sowerby, 1821), and C. obovata (Wood, 1861), from the Eocene of England, France, and Belgium, also have been placed within Claibornicardia (Pacaud and Le Renard, 1995; Tracey et al., 1996; Vervoenen and van Nieulande, 2010). These species, together with C. acuticostata, should potentially be assigned to a different genus converging with the American species, because they have less elongated outlineswith a lesswell defined posterior area and a fewer radial ribs. There are other records from the Eocene of Colombia and Jamaica that are doubtfully assigned to C. alticostata because they are based on incomplete specimens in which the diagnostic characters cannot be recognized (Anderson, 1928; Cox, 1941). Kafanov et al. (2001) recorded C. keenae from the late Paleocene Getkilninskaya Formation (Kamchatka,Russia;Kafanov andOgasawara, 2006). This record, together with C. keenae from the late Paleocene Lodo Formation
(California, USA, Johnson and Graham, 2007), are the most ancient records known for the genus Claibornicardia.
Claibornicardia paleopatagonica (Ihering 1903) Figure 3.1, 3.2, 3.4, 3.5
1903 Cardita paleopatagonica Ihering, p. 215, pl. 2, fig. 12. 1907 Venericardia paleopatagonica (Ihering); Ihering, p. 47. 1914 Venericardia paleopatagonica (Ihering); Ihering, p. 44. 1936 Venericardia paleopatagonica (Ihering); Feruglio, p. 232, pl. 23, figs. 28, 29.
1938b Venericardia paleopatagonica Mancini, p. 261.
(Ihering); Fossa
1977 Venericardia camachoi Vigilante, p. 20, pl. 1, fig. 6. 1987 Venericardia paleopatagonica (Ihering); Farinati et al., p. 154, pl. 1, fig. 5.
1995 Glyptoactis paleopatagonica (Ihering); Rodríguez et al., p. 243, pl. 2, fig. G.
1995 Glyptoactis sp. (Ihering); Rodríguez et al., p. 243, pl. 2, fig. H.
1996 Cardita paleopatagonica Ihering; Parodiz, p. 246. 2012 Venericardia (Pacificor) iheringi (Böhm); Scasso et al., p. 43, fig. 4G.
Type specimen.—Holotype MACN-Pi 360, articulated shell from ‘Río Chico’ (Chubut Province, Salamanca Formation).
Diagnosis.—Outline subrectangular to subovate with rounded posterior margin. Lunule deep. Right anterior tooth inclined backwards, placed on anterior side of left anterior socket. Radial ribs (30–33) sculptured with closely spaced subcircular nodes and with narrow intercostal spaces.
Occurrence.—General Roca and Coli Toro Plateau areas (early Danian, Roca Formation, Río Negro Province), Opaso (early Danian, Jagüel Formation, Neuquén Province), and Río Chico’s area (early Danian, Salamanca Formation, Chubut Province).
Description.—Shell thick, medium-sized, subrectangular to subovate in anterior-posterior direction, with elongate outline; posterior rounded, slightly curved ventral and gently inclined dorsal margins; posterior area defined by smooth convexity change starting from the eighth rib. Small umbones placed near anterior fifth of valve length. Lunule small, vertical, slightly concave, demarcated by an incised groove from remaining surface of shell, sculptured with fine commarginal growth lines. Right valve hinge with sinuous ventral edge below middle
tooth; small, short anterior tooth inclined backwards, thin, parallel to middle tooth, placed on anterior side of left anterior socket; middle tooth triangular, inclined strongly backwards, with narrow base, fine striations on dorsal surface, higher towards apex in lateral view; posterior tooth thin, slightly curved, taller than anterior one but shorter than middle tooth. Left valve hinge with almost straight ventral edge; anterior
tooth elongate, triangular, inclined backwards, slightly curved, with straight anterior and curved posterior sides; posterior tooth elongate, narrow, straight, with narrow base and acute apex, equal in height to anterior tooth.
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