Camptonectes tutorae Casadío, Griffin & Parras, 2005
CASADÍO, S., M. GRIFFIN & A. PARRAS. 2005. Camptonectes and Plicatula (Bivalvia, Pteriomorphia) from the Upper Maastrichtian of northern Patagonia: palaeobiogeographic implications. Cretaceous Research, 26: 507-524. [p. 511, fig. 3]
2005 Camptonectes tutorae Casadío, Griffin & Parras, 2005
S. Casadío, M. Griffin & A. Parras, 2005, figure 3.
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«1919 Pecten (Camptonectes) n. sp. Fritzsche, pp. 361, 362.
Derivation of name. After Claudia Montalvo, ‘‘La Tutora’’ (Universidad Nacional de La Pampa), in recognition of her numerous contributions to the
understanding of Cenozoic vertebrate faunas of La Pampa (Argentina). Material. Holotype, an articulated shell, GHUNLPam 1521; 83 paratypes (15 left and 17 right valves, 51 unassigned). Localities are as follows (Fig. 1): Salitral de La Amarga (36° 33´ S, 68° 9´ W): GHUNLPam 1521; Arroyo Las Aucas (34° 41´ S, 69° 34´ W): GHUNLPam 15220–15232; Laguna Amarga (34° 46´ S, 69° 33´ W): GHUNLPam 15236-15237, 15246–15250, 15294, 15374–15376; Puesto La Manga (34° 56´ S, 69° 40´ W): GHUNLPam 15738–15744; Arroyo Las Ramaditas (34° 54´ S, 69° 32´ W): GHUNLPam 10919–10920, 10969–10973, 15040–15059; Portezuelo Vega del Loro (34° 44´ S, 69° 39´ W): GHUNLPam 15105, 15187–15191; Puesto La Bebida (35° 26´ S, 69° 44´ W): GHUNLPam 10760–10763, 10802; Arroyo Brea (35° 31´ S, 69° 43´ W): GHUNLPam 10137; Arroyo Loncoche (35° 41´ S, 69° 40´ W): GHUNLPam 10108–10110; Cerro Butaló (35° 50´ S, 69° 40´ W): GHUNLPam 10302–10306, 10420–10423; Ranquil-Có (36° 12´ S, 69° 30´ W): GHUNLPam 15628, 15678.
Fritzsche’s two specimens (both unnumbered) of Pecten (Camptonectes) n. sp. are housed in the Goldfuss Museum (University of Bonn, Germany). Stratigraphic occurrence. Jagüel Formation (province of La Pampa), Jagu¨ el and Roca formations (province of Mendoza), Argentina; zone CC26, late Chron 30Ne Chron 29R, Upper Maastrichtian.
Diagnosis. Shell width slightly exceeding height; outer surface of early stages covered by 20 antimarginal striae, the number of which increases by irregular intercalation after successive growth halts to about 74-90 along the margin of adult shell; commarginal growth lines spaced 1e3 mm apart; surface between striae flat, averaging about 4-5 times (but ranging between 3 and 6) the width of striae along central part of ventral margin.
Description. Shell near-equivalve (right valve slightly flatter), disc broadly subtriangular, small to mediumsized (average height, 17.5 mm; maximum height, 27.7 mm), slightly longer than high (H/L ratio, 0.98); anterior margin weakly concave, posterior margin straight and longer than anterior, and both diverging from umbo at an angle of 80–85°; right valve with an extended anterior auricle, the length of which is about twice its height, with a straight dorsal margin and rounded ventral margin, sharply separated from the disc by groove left behind by shallow byssal notch; posterior auricle smaller and triangular; outer surface covered by numerous, very fine antimarginal striae, separated by flat surfaces that range in width from three (near anterior margin) to six (central part of ventral margin) times the width of striae; striae maintaining constant width throughout disc, but intervening spaces becoming wider towards margins; striae running uninterruptedly from one growth halt (lamella) to the next, their number increasing after each growth pause and thus appearing to bifurcate, but they actually appear on a new growth stage intercalated between the ends of adjacent striae of the previous growth stage; commarginal growth lines variably spaced at about 1–3 mm from each other; growth lines almost imperceptible on central area of disc, but becoming finely lamellose on anterior region, especially within area separating disc from auricle; some specimens show more widely separated commarginal lamellae that divide the shell surface into bands of antimarginal ornament; both kinds of ornament persist on both auricles, in addition to three or four radial ribs especially developed on anterior auricle.
Dimensions. Holotype: H, 27.7 mm; L, 31.4 mm; W, 8.8 mm.
Discussion. The outer shell ornament is well marked, consisting of antimarginal striae typical of Camptonectes. Fritzsche (1919) mentioned a new species of Camptonectes from southern Mendoza (Arroyo Loncoche), which he compared (yet did not formally name, nor illustrate) with Pecten (Camptonectes) curvatus Geinitz sensu Stoliczka (1871, p. 433, pl. 31, figs. 15, 16) from the Trichinopoly Group of southern India. This most likely belongs to Camptonectes tutorae sp. nov. The Indian material and the new species have the same ornament in common (about 50 striae near shell margin in the former), and shell size and umbonal angle are closely similar; apparently the right valve is flatter than the left. Stoliczka (1871) noted that in P. (C.) curvatus the ornament of the right and left valves differed, that of the former being notably finer. This may also be the case for C. tutorae, but better-preserved material of both valves is needed to be certain.
Rodríguez et al. (1995) mentioned Camptonectes from the Maastrichtian Coli Toro Formation of the province of Río Negro (Argentina), but failed to provide descriptions and illustrations, so that conspecificity with the new species cannot be proved. In contrast, specimens from the Jagüel and Roca formations in La Pampa and Mendoza recorded by Casadío (1994, 1998) and Feldmann et al. (1995) undoubtedly belong here. From the Cerro Cazador Formation (Maastrichtian) in the Austral Basin of southern Patagonia, Wilckens (1905, p. 26, pl. 4, fig. 10) described Pecten (Camptonectes) malignus, based on an external mould of a right valve. However, re-examination of the type material (Museum of La Plata, MLP 9007), shows that this probably belongs to a different group as the shell is strongly convex and the antimarginal striae are far more numerous and present only along a narrow band near the shell margin, while the central part of the disc is smooth. From older Cretaceous rocks, also in the Austral Basin but further north (Lago Belgrano), Hatcher collected material referred to as Pecten (Camptonectes) pueyrredonensis by Stanton (1901, p. 12, pl. 4, fig. 1). Although the ‘‘Camptonectes’’ microsculpture does occur, it is restricted to the shell margins; moreover, the auricles are completely smooth and the shell is far more strongly convex than in Camptonectes tutorae. Our material shows a striking resemblance to C. nordestensis (de Oliveira in Löfgren and de Oliveira, 1943) (p. 44, pl. 4, figs. 1–3, non 5), from Sergipe (NE Brazil). The material, from a core, is rather poorly preserved, but reveals that the nominal species includes two distinct taxa, only one of which (their pl. 4, figs. 1–3) belongs to Camptonectes. These specimens have a relatively wide umbonal angle and there are about 80 antimarginal striae at the shell margin in the presumed adult specimen illustrated in their pl. 4, fig. 1. However, on the basis of the type series the range of variation cannot be determined; additional material is needed to document further affinities with the present collection. The only difference between these taxa appears to be the slightly more regular arrangement of antimarginal striae over the shell surface in the Brazilian species. Camptonectes tutorae also appears to be closely related to C. virgatus (Nilsson, 1827) (p. 22, pl. 9, fig. 15), a long-ranging (Cenomanian–Upper Maastrichtian) and widely distributed (Europe, Africa, India and New Caledonia) taxon (Dartevelle and Freneix, 1957; Freneix, 1958; Dhondt, 1972). As pointed out by Dhondt (1972), C. virgatus is extremely variable in both shell size and proportions and ornament (see Dhondt, 1972, pl. 2, fig. 1c; this specimen shows fewer (82) antimarginal striae, and thus is close to our material). Perhaps further study may lead to a better understanding of such variation and its taxonomic significance. The two species differ in the longer posterior margin of C. tutorae, which also has shells that are slightly longer than high. Antimarginal striae in C. virgatus number about 120 along the ventral margin of the shell, and are thus much more densely packed, apart from ‘‘odd’’ specimens such as the one illustrated by Dhondt (1972, pl. 2, fig. 1c). Pecten kamerunensis von Koenen, 1897 (p. 20, pl. 3, figs. 14, 15) and P. productus von Koenen, 1897 (p. 20, pl. 3, fig. 17a, b) were synonymised by Dartevelle and Freneix (1957), with C. virgatus var. kaffraria, a form originally described (Rennie, 1930, p. 178, pl. 16, figs. 12–15) from the Upper Cretaceous of Pondoland. Dartevelle and Freneix (1957, p. 70, pl. 9, figs. 3a, b, 4–7) recorded it from the Lower Turonian and ‘‘Senonian’’ of Cameroon, the Lower Santonian of Gabon, the Cenomanian and Turonian–‘‘Senonian’’ of Congo and the ‘‘Senonian’’ of Angola. Material described as Pecten (Camptonectes) cf. curvatus Geinitz, 1843 by Reyment (1957, p. 42, pl. 7, fig. 10) from the Odukpani Formation in Nigeria is based on specimens that are too poorly preserved for any detailed comparison. Pecten curvatus was considered by Dhondt (1972) to be synonymous with Pecten virgatus; however, a determination of the range of variation of these two species is needed to prove their conspecificity. Another species that is similar in size, shape and ornament is C. moodyi (Stephenson, 1952) (p. 79, pl. 19, figs. 8, 9) from the Cenomanian Woodbine Formation of Texas. The umbonal angle is similar to that of C. tutorae, and it has approximately the same number of striae along the shell margin, and thus a comparable ‘‘density’’. However, it differs in showing more strongly impressed antimarginal striae, better developed growth lines, and a shell height that exceeds its length. Auricle ornament also differs in that the weak radials and lamellose commarginals seen in C. tutorae are missing. Similar to C. moodyi is C. ellsworthensis Stephenson, 1952 (p. 80, pl. 19, figs. 5, 6), based on material collected at the same localities and from the same strata. This differs from C. moodyi only in showing a finer ornament (i.e., more closely packed striae, about 100 along shell margin). This, together with the slightly narrower umbonal angle and taller shell, suffice to differentiate it from C. tutorae. Of two other species described by Stephenson (1952), C. martinsensis (p. 80, pl. 19, figs. 1–4) appears to represent juveniles of C. moodyi, while C. cavanus (p. 80, pl. 189, fig. 7) is based on two poorly preserved specimens, whose ornament cannot be clearly observed. Stephenson (1954, p. 30, pl. 7, figs. 1, 2) described material from the Cenomanian Raritan Formation (New Jersey) as Pecten (Camptonectes) sp. Although poorly preserved, Stephenson was right in pointing out its resemblance to C. ellsworthensis, showing the same kind of densely packed striae. Again, this easily differentiates it from the new Patagonian species. ‘‘Pecten’’ argillensis Conrad, 1860 (p. 283; see also Wade, 1926, p. 62, pl. 20, figs. 8, 9), ‘‘Pecten’’ simplicius Conrad, 1860 (p. 283, pl. 46, fig. 44; see also Wade, 1926, p. 62, pl. 20, fig. 7), and ‘‘Pecten’’ burlingtonensis Gabb, 1861 (see Wade, 1926, p. 63, pl. 20, figs. 5, 6, 10, 11) from the Ripley Formation at Coon Creek (Tennessee) all show a well-developed ‘‘Camptonectes’’ ornament, yet have strong commarginal costae missing in the present specimens. In addition, at least in ‘‘P.’’ argillensis and ‘‘P.’’ burlingtonensis, the hinge shows strong dorsal and resilial teeth, a feature not visible in C. tutorae, although it should be noted that most specimens lack well-exposed hinges. Although C. tutorae is similar in size and shape to Camptonectes sp. mentioned by Perrilliat et al. (2000) from the Lower Maastrichtian of southern Mexico, the latter lacks any trace of external ornament. There are two more Late Cretaceous taxa in the Southern Hemisphere: C. hectori (Woods, 1917) (p. 26, pl. 11, figs. 6–9; pl. 12, fig. 1) from southern Marlborough and northeastern Canterbury, South Island (New Zealand), and Camptonectes sp. (Stilwell, 1998, p. 40, fig. 5b–d) from the SantonianeMaastrichtian Kahuitara Tuff (Campbell et al., 1993) on Pitt Island (Chatham Islands, New Zealand). Camptonectes hectori is represented by a few, badly worn valves that do show the typical ‘‘Camptonectes’’ sculpture, but the number and distribution of striae cannot be determined. The anterior margin seems to be far more concave than in Argentinian material and the byssal sinus is much deeper and the umbonal angle narrower. Such features show that these taxa are not conspecific. Camptonectes sp. is close but shows typically pitted antimarginal striae, while striae in C. tutorae are almost completely smooth, except near the anterior and posterior margins. Stilwell’s material shows approximately 120 antimarginal striae along the ventral margin, i.e., significantly more than in C. tutorae. The ornament of Eburneopecten freneixae Stilwell, 1998 (p. 41, fig. 6a–c, e, f, h, k), also from the Kahuitara Tuff, is remarkably similar to that of C. tutorae in comprising about 80 antimarginal striae along the shell margin (Stilwell noted only 53). However, a closer look has revealed that E. freneixae possesses crurae (or teeth, sensu Waller, 1991); in C. tutorae these are very much reduced, or even lacking, as seen in the few specimens showing internal features. In addition, shell margins in the former are ‘‘weakly crenulated’’ according to Stilwell (1998), which would suggest some kind of internal fluting, albeit weak. This is a phylogenetically important feature which is missing in C. tutorae. Stilwell (1998) indicated Indopacific/Tethyan affinities for E. freneixae, but later (Stilwell, 2000) suggested an austral origin for it. However, too little is currently known about the taxonomy and relationships of pectinids of the Eburneopecten group to assess its biogeographic distribution properly. In addition, whether or not material referred to Camptonectes by Stilwell (1998) really belongs in that genus, or alternatively, represents Eburneopecten with more densely packed antimarginals, remains to be determined. Unfortunately, no interiors are yet available to resolve this matter.» SILVIO CASADÍO, MIGUEL GRIFFIN & ANA PARRAS, 2005
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