Stilwell—Oldest volutes from early Paleogene
growth lines moderately strong, prosocline adapically, broadly sinued below with apex at inception of pronounced axials at periphery; neck moderately long, slightly twisted to the left with poorly developed or obsolete notch; inductura moderately broad, but mostly thin; columella with three medially situated oblique plaits.
Paleobiogeographic element.—Endemic and Paleoaustral.
Discussion.—The enigmatic Wangaluta n. gen. is proposed as an apparently endemic group of volutes characterized by a medium-sized shell, fusiform to volutiform outline, strong subsutural adapical welt and constriction on the last whorl interrupting well-developed axially extending ribs, weak spiral sculpture, pronounced basal constriction producing a moderately long neck with a poorly developed siphonal notch, and columella with three plaits. Wangaluta n. gen. does not appear to be closely allied with any particular volutid genus, but combines characters present in several groups. In terms of sculpture (e.g., long axially extending ribs on the last whorl and shortened extreme abapical sutural ribs on spire whorls that are mostly concealed by succeeding whorls), suture and excavated spire whorls with medial concavity adjacent to axial ribs and sutural swellings, Wangaluta henaconstricta n. gen. n. sp. is consistent with described zidonine species within Alcithoe H. and A. Adams, 1858, and A. (Leporemax) Iredale, 1937. On the other hand, the strong basal constriction, followed by an extended neck and ill-defined siphonal notch in W. henaconstricta, is atypical of species of Alchithoe s.s. and Alchithoe s.l. Wangaluta is doubtfully allied with
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Zidoninae. The similarity of sculpture in Wangaluta n. gen. and that of Zidoninae are herein considered to be homeomorphic. Wangaluta is possibly allied with the fulgorariine genus
and subgenera Fulgoraria Schumacher, 1817, s.s., Fulgoraria (Psephaea Crosse, 1871) and F.(Musashia Hayashi, 1960). Sculpture, coupled with the variably constricted basal part of the last whorl in these groups, is consistent with Wangaluta n. gen., but the neck of Wangaluta is generally longer and narrower, the basal constriction is much more rapid, the last whorl has an adapical subsutural swollen band and adjacent constriction, and the spire whorls are subtrapezoid with a medial concavity interrupting the strong axial ribs, very much distinct from the previously described fulgorariines. Wangaluta seems more akin to fulgorariine volutes than to zidonine taxa, but as with Zidoninae these similarities may be superficial and homeomorphic. A further possibility is that Wangaluta may be allied with
ptychatractine genera in Turbinellidae such as Benthovoluta Kuroa and Habe, 1950, which includes species with long necks and slightly to moderately constricted bases (see species figured in Harasewych, 1987), but the sculpture of Wangaluta is distinct compared with these taxa and there is no subsutural swelling or band, subdued axial sculpture, and no clasping sutures in species of Benthovoluta. Wangaluta is, thus, placed tentatively in Fulgorariinae.
Etymology.—Genus named for its discovery at Wangaloa, southeastern Otago, and for its inferred relationship to Volutidae.
Figure 5. Global paleogeography of the Earth at the Cretaceous-Paleogene boundary ca. 66Ma with distribution of the Paleocene volutes figured and described in this paper: Wangaluta henaconstricta n. gen. n. sp., W.? neozelanica (Finlay and Marwick, 1937), Alcithoe s.l. wangaloaensis n. sp., Fulgorariine? gen. indet. sp. indet. (all from the Wangaloa Formation and latter from the Steel Greensand), and Teremelon onoua n. sp. from the Red Bluff Tuff of Chatham Islands. Red bar indicates volute species described in this paper from South Island, New Zealand, and not evolutionary relationships. Yellow bar points to Chatham Islands; note the position of the Chathams in the late Paleocene, which was between 50°S and 55°S, and some 10° further south, compared to their present location. Palaeogeographic base map after Ron Blakey (Colorado Plateau Geosystems, Inc
http://cpgeosystems.com/index.html).
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