Cyprideis paralela ( Purper, 1979 )

Gross, Martin, Ramos, Maria Ines F. & Piller, Werner E., 2014, On the Miocene Cyprideis species flock (Ostracoda; Crustacea) of Western Amazonia (Solimões Formation): Refining taxonomy on species level, Zootaxa 3899 (1), pp. 1-69 : 20-21

Cyprideis paralela ( Purper, 1979)

Fig. 4o ; Pl. 4, Figs. 30–45

* 1979 Pseudoparakrithella paralela Purper , gen. et sp.nov. —Purper: 238–239; Pl. 6, Figs. 7 –14.

1983 Pseudoparakrithella paralela Purper, 1979 —Purper & Pinto: 118; Pl. 2, Figs. 14–16.

1985 Pseudoparakrithella paralela Purper, 1979 —Purper & Pinto: 427, 430; Fig. 2 .

Material. 97 valves; samples AM 10/15, 22–25, 30.

Dimensions (total range over all samples). R ♀ l = 0.59–0.65 (0.62), h = 0.30–0.32 (0.31; n = 5); L ♀ l = 0.62–0.67 (0.64), h = 0.30–0.32 (0.30; n = 5); R ♂ l = 0.59–0.66 (0.63), h = 0.28–0.30 (0.29; n = 3); L ♂ l = 0.57–0.63 (0.61), h = 0.28–0.29 (0.29; n = 4).

Remarks. These specimens belong to a group of rather small-sized Cyprideis species with approximately parallel dorsal and ventral margin, with an inverse hinge with long crenulated anterior and posterior bars, a short anteromedian crenulated groove and a short, crenulated, inconspicuous posteromedian tooth (left valves). The valves available here have an elongated-ovate shape in lateral view, are smooth (except normal pore canal openings), have a comparably small inner lamella with a narrow fused zone and simple marginal pore canals (a few branched canals can be observed on the anteroventral thickening of the inner lamella) and a well-developed vestibulum.

Variation in size and outline between samples is small as far as it can be examined on the limited material. However, specimens of AM10/30 (Pl. 4, Figs. 36–45) display a distinct internal “eye-spot” ( Purper & Pinto 1985), which is missing in the samples up-section. Only in some badly preserved right valves of AM10/25 a slight thickening below the anterior crenulated hinge element may correspond to that remarkable structure.

Four species are comparable with the current material: Botulocyprideis simplex Sheppard & Bate, 1980 , Pseudoparakrithella paralela Purper, 1979 , Nealecythere posterocompressus Purper & Pinto, 1983 ( Whatley et al. (1998) put these three genera into Cyprideis ) and Cyprideis sp. 2 in Gross et al. (2013).

Muñoz-Torres et al. (1998) and Whatley et al. (1998) placed C. simplex and C. paralela as well as Cyprideis multiradiata ( Purper, 1979) into the synonymy of Cyprideis olivencai . These authors used a broad species concept, which results in a “very variable” species definition. As shown in chapter 4.5.5., C. multiradiata is a valid taxon and cannot be joined with C. olivencai . Likewise, the species group around C. paralela ( C. simplex , C. paralela , C. posterocompressus , Cyprideis sp. 2 ) forms a distinct lineage ( Purper & Pinto 1985) and C. simplex and C. paralela are clearly not synonyms of C. olivencai (note: C. paralela ( Purper, 1979) must not be confused with the Central European species Cyprideis parallela Krstić, 1968b ).

Cyprideis sp. 2 from the Late Miocene of the Eirunepé region ( Gross et al. 2013) differs from the core material by its coarsely punctate to reticulate ornamentation and its occasionally observable 2–3, inconspicuous posteroventral denticles. An eye-spot as well as the extension of the flange on the lower half of the posterior margin (left valves) are always missing.

C. simplex (see below) can be distinguished because it has no vestibulum, resulting in a wider anterior fused zone with more frequently bifurcated marginal pore canals ( Sheppard & Bate 1980; Purper & Pinto 1983, 1985).

C. posterocompressus diverge insignificantly by a slightly narrower fused marginal zone and a somewhat wider vestibulum. These differences are vague compared to the variation observed within one sample between right and left valves (left valves seem to have a wider vestibulum than right valves). Due to the well-developed eye-spot, especially the specimens from AM10/30 are very close to C. posterocompressus . The main difference is that the current material lacks the diagnostic external posterior depression on left valves ( Purper & Pinto 1983). Remarkably, already Purper & Pinto (1983) mentioned a transition of this trait between C. posterocompressus and C. paralela (pers. observ., M.I.F.R.: among the type material of C. posterocompressus only males display that depression; compare also Fig. 1 on plate 2 of Purper & Pinto (1983), where this feature appears to be lacking on the female carapace). Based on our material, we are not in the position to decide if the indistinct differences in the inner lamella, the expression of the eye-spot and the compressed posterior proportion in left valves are sufficient for a delineation of C. posterocompressus from C. paralela .

C. paralela has originally been described being a punctate species with simple marginal pore canals. Initially, an internal eye-spot has not been mentioned but can be anticipated on the figures in Purper (1979; e.g. Pl. 6, Fig. 12). However, in their re-evaluation of that species Purper & Pinto (1985: 427, 430) assigned that species to “a peculiar lineage of very smooth forms” and recognized an “internal eye protuberance”. The anterior part of the inner lamella is of “intermediate type ” (narrower vestibulum but wider fused zone than C. posterocompressus but with vestibulum and shorter pore canals than C. simplex ; Purper & Pinto 1983). The characters of our material fit best with C. paralela to which we here assign it.

In core 1AS-32-AM Purper & Pinto (1985) discussed an evolutionary trend starting in the lower part with C. simplex (no vestibulum, long, bifurcated, anterior marginal pore canals, no eye-spot) and leading to C. posterocompressus (large vestibulum, short, simple pore canals, prominent eye-spot) up-section, with C. paralela as an intermediate species in the middle part of the core. Comparably, at core 1AS-10-AM, C. simplex occurs only in the lower part (AM10/40–39), followed by C. paralela up-section (AM10/30–15). However, valves with welldeveloped eye-spots are restricted to AM10/30, which appears to contradict the observation of Pinto & Purper (1985; most prominent eye-spots in the upper part). Possibly, the expression of the eye-spot is rather ecologically controlled than a phylogenetic character.

Occurrence (of C. olivencai sensu Muñoz-Torres et al. 1998 ). Western Amazonia ( Brazil, Colombia, Peru), early Middle to early Late Miocene ( C. aulakos – C. cyrtoma zone; Muñoz-Torres et al. 2006; chronostratigraphic correlation after Wesselingh & Ramos 2010). Up to now only recognized in Brazil (cores CPCAN-III-São Paulo de Olivença and CPCAN-I-Tamanduá; Purper 1979; core 1AS-32-AM; Purper & Pinto 1983, 1985).

Figures

FIGURE 1. Location of the study area in western Amazonia. a: Isopatches [m] of the thickness of the Solimões Formation in the Acre and Solimões Basins (after Maia et al. 1977; Latrubesse et al. 2010); b: Coal-prospection area with isopatches [m] of the Solimões Fm. and position of exploration wells (after Maia et al. 1977; star = herein investigated core 1AS-10-AM; additional boreholes marked with numbers are mentioned in this study; location of CPCAN-I–III after Nuttall 1990).

FIGURE 2. Section of well 1AS-10-AM (γ-log, lithology, samples, macrofossil content and core intervals; based on unpublished CPRM report and own observations).

FIGURE 4. “Smooth” Cyprideis species of core 1AS-10-AM (except Figs. j–k = core 1AS-32-AM) photographed in transmitted light (external view) and focus stacked (scale bar = 200 µm; L/R = left/right valve; ♀/♂ = female/male; l/h = length/height [mm], specimen code = sample number_specimen number). a–c: C. amazonica, a: L♂ (0.84/0.46; AM10-39_44), b: R♀ (0.85/0.46; AM10-7_94), c: R♀ (0.74/0.42; AM10-39_42); d–f: C. machadoi, d: L♀ (1.09/0.58; AM10-23_66), e: L♀ (1.06/0.53; AM10-27_74), f: R♂ (1.08/0.51; AM10-27_73); g–k: C. kotzianae, g: R♂ (0.83/0.38; AM10-27_75), h: L♀ (1.00/ 0.46; AM10-30_36), i: R♂? (0.95/0.43; AM10-30_117), j: L♀ (0.87/0.41; AM32-5_26), k: R♀ (0.86/0.40; AM32-5_39); l–m: C. olivencai, l: L♀ (0.73/0.38; AM10-7_97), m: R♀ (0.75/0.38; AM10-7_96); n: C. kroemmelbeini, L♀ (0.83/0.41; AM10- 7_100); o: C. paralela, R♀ (0.61/0.30; AM10-30_100); p–r: C. multiradiata, p: L♀ (0.78/0.37; AM10-30_116), q: L♂ (0.89/ 0.38; AM10-30_114), r: R♂ (0.89/0.37; AM10-30_113).

FIGURE 7. Variation of some traits in C. sulcosigmoidalis (for ornamentation and selvage position specimens were assigned to classes (1–3; ESM 2); if more than one class occur in one sample, the arithmetic mean is also displayed; the number of studied specimens per sample is indicated next to the bars; min = minimum, max = maximum, max range/sa = maximum range within one sample, Rf = right female valves).