Antarctipecten alanbeui (Jonkers, 2003)
JONKERS, H. A. 2003. Late Cenozoic-Recent Pectinidae (Mollusca: Bivalvia) of the Southern Ocean and neighbouring regions. Monographs of Marine Mollusca, 5: viii, 1-125 pp, pls. 1-17. Backhuys Publishers. [p. 70, pl. 3, figs. d, e, g; pl. 16, figs. a-h; pl. 17, figs. a-b]
2003 Adamussium alanbeui Jonkers, 2003
H. A. Jonkers, 2003, plate 3.
H. A. Jonkers, 2003, plate 16.
H. A. Jonkers, 2003, plate 17.
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«Etymology. Named after Alan G. Beu, Institute of Geological & Nuclear Science, Lower Hutt, New Zealand, in recognition of his important work on New Zealand pectinid stratigraphy and evolution, and for his major contributions to molluscan palaeontology of the New Zealand region.
Type material. IGNS, TM8228 (articulated pair, VH 35.2 mm; holotype, LV figured by Beu & Dell, 1989, fig. 11; Plate 16, fig. a),TM8229 (articulated pair, VH unknown [specimen incomplete]; paratype, figured by Beu & Dell, 1989, figs. 13,14; Plate 16, figs. b-d, Plate 17, figs. a, b), TM8230 (RV, VH c. 42 mm; paratype, figured by Beu & Dell, 1989, fig. 12), from CIROS-1 drillhole, 77º34'55" S,164º29'56" E, McMurdo Sound, Ross Sea, in 197.5 m water depth, 454.39 mbsf, 215.57 mbsf,174.64 mbsf, respectively, P.J. Barrett leg., 15 Nov. 1986. All specimens at IGNS; latex peels of TM8229, 8230 at BAS under AR.1.1-2. Material examined. 5 pairs, 1 ?LV lRV several indeterminate valves (all internal and external moulds), from the Oligocene of CIROS-I and Late Oligocene-Early Miocene section of CRP-2/2A drillhole, the Oligocene Polonez Cove Formation, King George Island, South Shetland Islands, and from the earliest Miocene Cape Melville Formation, King George Island; lodged at BAS and IGNS (see Appendix). Description. Shell of relatively small size (VH mostly <50 mm; ?up to 60 mm [P.2853.1B]); acline; weakly convex, with LV slightly more conyex than RV; umbonal angle narrow for genus (c. 110º - 120º). No radial macrosculpture. Microsculpture of narrow antimarginal ridgelets. Auricles slightly asymmetrical (OLA/OLP 1.1-1.3); LV anterior auricle with free margin curved to anterior (Plate 17, fig. b); RV anterior auricle with very shallow byssal notch (Plate 17, fig.a). Remarks. Adamussium alanbeui sp. nov. differs from A. colbecki in its smaller size, less convex valves, and the lack of radial costation and commarginal lirae. A further difference with A. c. colbecki is the straight hinge. Two internal moulds of paired valves (P.2702.1009, 1042; Plate 16, figs. g, h) from the earliest Miocene Cape Melville Formation at Cape Melville, King George Island, are identical to moulds of Oligocene A. alanbeui from CIROS-I and from Godwin Cliffs (Lions Rump area, King George Island; Plate 16, fig. e); however, one mould of a presumably LV has c. 7 very low radial costae (P.2702.832; Plate 16, fig. f). As no further material from this Miocene deposit was available these fossils are tentatively included in A. alanbeui. Stratigraphical range and distribution. Oligocene-Early Miocene (c. 30-20 Ma [Dingle et al., 1997; Lavelle, 2000]; Fig. 25). A. alanbeui is the oldest known species of Adamussium; it is known only from the Ross Sea (CIROS-1 and CRP-2/2A drill cores; Figs. 3, 10) and from King George Island, South Shetland Islands (Lions Rump area and Cape Melville; Figs. 3, 4), where it is rare. In the Lions Rump area it occurs together with abundant Austrochlamys gazdzickii sp. nov.» H. A. JONKERS, 2003
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«Distribution. Antarctipecten gen. nov. alanbeui is recorded from late Early Oligocene to late Early Miocene (Rupelian–Burdigalian) rocks in drill cores in the Ross Sea and from outcrops on King George Island. It is assumed to have had only a Rupelian–Burdigalian age range (c. 30–16 Ma), although both its upper and lower limits are poorly constrained. These are all the possible Antarctic localities of Oligocene and Early Miocene age, suggesting that A. alanbeui had a circum-Antarctic distribution.
Dimensions. Holotype: H = 34.9, L = 32.6 mm; paratype TM8230, LV: H (slightly incomplete) = 43.9, L = 45.7 mm; USNM 545823, ANDRILL 2A, 376.80–376.85 mbsf: fragmentary LV, H = 12.8, L = 13.0 mm; USNM 545824, fragmentary RV, H 9.6, L 10.8 mm; USNM 545846, 999.76–999.80 mbsf, remaining fragment: RV H 28.9, L 35.9 mm; LV H = 20.6, L = 35.4 mm. Jonkers (2003, p. 70) mentioned specimens possibly reaching up to H = 60 mm, but we have not seen specimens larger than H = 45 mm.
Diagnosis. Shell small (H up to 50 mm, few specimens exceeding 45 mm), very thin, fragile, acline; auricles almost symmetrical, short; umbonal angle low (c. 110–115 degrees); without obvious macrosculpture, other than faint, very narrow radial costae on LV of a few well-preserved specimens, particularly on anterior half of disc; microsculpture of obvious commarginal ridges, raised into high lamellae in groove between disc and auricle on well-preserved specimens; and fine antimarginal ridgelets.»
BEU, A. & M. TAVIANI. 2014. Early Miocene Mollusca from McMurdo Sound, Antarctica (ANDRILL 2A drill core), with a review of Antarctic Oligocene and Neogene Pectinidae (Bivalvia). Palaeontology, 57 (2): 299-342, figs. 1-9. [p. 324]
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Antarctipecten gen. nov. alanbeui (Jonkers, 2003); A. G. Beu & M. Taviani, 2014, Early Miocene Mollusca from McMurdo Sound, Antarctica (ANDRILL 2A drill core), with a review of Antarctic Oligocene and Neogene Pectinidae (Bivalvia), figures 7B-7E.
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