Stilwell—Oldest volutes from early Paleogene
Discussion.—Teremelon Marwick, 1926, ranges from the late Paleocene-earliest Eocene (this work) to the Recent and, as such, is one of the world’s longest ranging volutid gastropods with the acme in its diversity being reached in the mid-Cenozoic in the Altonian Stage (late early Miocene) in New Zealand. In relative terms, Teremelon species are small volutes in the Zidoninae, have all but no axial sculpture except sometimes on the early whorls, characteristically have a moderately deep anterior notch, and a poorly developed fasciole (Beu and Max- well, 1990, p 205). Teremelon onoua n. sp. probably lived in shallow waters in the Red Bluff Tuff, but more recent taxa such as T. knoxi (Dell, 1956), which is the sole survivor of the Ter- emelon lineage, is restricted to the upper bathyal zone today between 220 and 320 fathoms and some fossil taxa are inferred to have lived in the inner to mid-shelf (Powell, 1979; Beu and Maxwell, 1990), including T. onoua n. sp.
Teremelon onoua new species Figure 6D, 6E
1990 Teremelon Beu and Maxwell, p. 205. 1993 Teremelon n. sp. Campbell et al., p. 85, tab. 4.11; 1994 Teremelon Stilwell, p. 1027; 2009 Teremelon Beu and Raine, no page number for Miscellaneous Series No. 27 (web reference).
Diagnosis.—Shell relatively large to moderately so at approxi- mately 70mm, if complete, and thick fusiform with at least six teleoconch whorls that are slightly angulate on youngest three whorls; spire higher compared to other fossil species; siphonal canal long and slightly twisted; columella with four very well- developed plaits that are more oblique closer to canal and more sub-horizontal toward suture; outer lip moderately thick.
Description.—Shell moderately large to large for subfamily (c. 70mm with protoconch preserved), modetately thick, high- spired fusiform, spire 0.4 total height; spire moderately high, of at least five teleoconch whorls, becoming weakly angulate to convex by antepenultimate whorl, nearly straight on early tele- oconch whorls; whorl inflation rapid in early whorls, becoming very rapid from penultimate to last whorl; spire angle approxi- mately 36°; protoconch unknown, but prominent in other fossil forms of 1.5 squat, mamillate whorls; sutures weakly impressed, somewhat clasping around older whorls and declivous; last whorl moderately inflated, elongate-ovate and convex, smooth with no axial or spiral sculpture, and only very weak growth lines; minor repaired break noted approximately 10mm from outer lip on last whorl; aperture narrow, constricted both aba- pically and adapically; shell siphonostomatous with narrow, deep notch, slightly twisted, siphonal canal; columella moder- ately long, slightly concave to mostly straight, bearing four, very well developed and equally spaced plaits centrally, third
and fourth fold becoming more inclined toward siphonal canal, first and second plaits sub-horizontal above; outer lip probably moderately thick, only partially complete
Dimensions.—Holotye TM 8917 height 69.5mm, diameter of last whorl 25.0mm; paratypes TM 8918 height 35.0mm, diameter 15.5mm (incomplete, partial teleoconch preserved);
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TM 8919 height 37.5mm, height 18.0mm (incomplete, partial last whorl and siphonal canal).
Types.—HolotypeTM8917, paratypesTM8918 andTM8919.
Type locality.—Flowerpot Harbour (‘Onoua’), north of Bluff Homestead, Pitt Island, Chatham Islands, New Zealand, GS12159, CH/f471, grid reference 713236.
Material.—Three specimens (one nearly complete, holotype), collected 1977.
Stratigraphic range.—Red Bluff Tuff Formation in pebbly, coarse, pale yellow-green brown calcareous, tuffaceous sand- stone and lapillistone in Section CI-2/1 at approximately 7.5m from base of section at sea-level and about 5m below uncon- formable contact with Onoua Limestone in same section (see Campbell et al., 1993, p. 228 for section details and stratigraphic log). The Red Bluff Tuff was dated radiometrically recently as approximately 53–48Ma by Németh et al. (2013).
Discussion.—Protracted, sporadic, volcanic pulses in the Chatham Islands region during the late Paleocene to early Eocene had a dramatic effect on invertebrate assemblages in the eastern Zealandian region, and it may have taken thousands of years between volcanic events to reach an acme in biotic assemblages Sorrentino et al., 2011, 2014). Many invertebrates (including gas- tropods, bivalves, cnidarians, poriferans, cirripeds, brachiopods, and others) are preserved in volcaniclastic and phreatomagmatic sedi- ments, resulting from Surtseyan-style eruptions in the region; it is surprising that many fossils, including Teremelon onoua n. sp. described here, are so well preserved, and some fossils escaped being crushed between tholeiite volcanic flows and eroded boulders of basalt, which eventually resulted in shoaling of marine waters, similar to those fossils preserved the older Upper Cretaceous Kahuitara Tuff of Pitt Island (Stilwell, 1997, 1998, 2014). Teremelon onoua n. sp. pre-dates the previously oldest
recorded member of the genus, T. striata (Laws, 1935) from the Bortonian Stage (late middle Eocene), by more than 10 million years. In terms ofmorphologic similarity, T. onoua n. sp. ismost closely allied with Neogene members of the genus, especially T. elegantissima (Suter, 1917) from the Altonian (Miocene) of
Weka Pass (see Scaphella elegantissima Suter, 1917, p. 41, pl. 5, fig. 9; Marwick, 1926, p. 280, pl. 72, fig. 1), but T. elegantissima is much smaller at 50mm height with a slightly higher spire and more developed, twisted siphonal canal. The type species, T. tumidior (Finlay, 1926) (p. 250, pl. 56, fig. 6; Marwick, 1926, p. 280, pl. 62, fig. 2; Beu and Maxwell, 1990, p. 204–205, pl. 21, fig. r), which spans the Duntroonian to Altonian stages (lateOligocene to late earlyMiocene), is distinct fromT. onoua n. sp. in being much smaller at a maximum height of 48mm and lower spired, relative to the Red Bluff Tuff species. In several decades of collecting in the Red Bluff Tuff on both Chathamand Pitt islands, only three Teremelon specimens have become known, all collected in 1977.
Etymology.—Species named after the Moriori name for Flowerpot Harbour (‘Onoua’), Pitt Island, Chatham Islands, where the type material was collected.
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