Journal of Paleontology, 90(1), 2016, p. 31–42 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2016.19


Zealandia’s oldest volutes (Mollusca: Gastropoda: Volutidae) from the early Paleogene of South Island and Chatham Islands: post Gondwana break-up and evolutionary divergence


Jeffrey D. Stilwell


School of Earth, Atmosphere and Environment, 9 Rainforest Walk (ex Bldg 28), Monash University, Clayton VIC 3800, Australia; and Australian Museum, 6 College Street, Sydney NSW 2000, Australia ⟨Jeffrey.Stilwell@monash.edu⟩


Abstract.—The isolation of Zealandia in the latest Cretaceous and early Paleogene following the final break-up of Gondwana fostered significant provincialism in molluscan faunas, concomitant with the segmentation of oceanic circula- tion patterns and changing climate nearing the end of the greenhouse phase in the Southwest Pacific. The earliest volutes (Gastropoda: Volutidae) from the Zealandian region reflect this isolation after separation from the Marie Byrd Land region of West Antarctica with several endemic groups being recognized for the first time since collecting first started in theWangaloa Formation at Mitchells Rocks (Wangaloa), South Island, New Zealand in 1869. Five taxa attributed to the Volutidae are described herein from South Island (Wangaloa Formation and Steel Greensand) and also the Chatham Islands (Red Bluff Tuff) from the early (mid-Danian) to late Paleocene (Thanetian?). These comprise a new mid-Danian fulgorariine? genus and species, Wangaluta henaconstricta n. gen. n. sp.; a new combination also from the Wangaloa Formation, Wangaluta? neozelanica (Finlay and Marwick, 1937); two new zidonine volutes, the mid-Danian Alcithoe. s.l. wangaloaensis n. sp. from the Wangaloa Formation, and also Teremelon onoua n. sp. from the late Paleocene-early Eocene of the Red Bluff Tuff; and a probable volute, Fulgorariine? gen. indet. sp. indet. from the mid-Danian of the Steel Greensand. All of these taxa are endemic in the early Paleogene of New Zealand and represent a significant boost in our knowledge of post-K-Pg boundary diversification of volutid gastropods in the shrinking Weddellian Biotic Province in the southern rim of the Pacific.


Introduction


Paleogene molluscan assemblages of the New Zealand and Chatham Islands region of the Southern Hemisphere provide crucial data on the post-Cretaceous-Paleogene (K-Pg) biotic recovery processes following the mass extinction event world- wide 66 Ma. New Zealand and the Chatham Islands today, along with New Caledonia and Lord Howe Island, comprise the emergent ca. 7% of a mostly submerged continent spanning nearly four million square kilometres extending from 19° south (but north of New Caledonia) to 56° south (south of New Zealand’s subantarctic islands)—collectively known as the geographic region of ‘Zealandia’ (Fig. 1). The separation of New Zealand and the Chatham Islands (i.e., Zealandia) from the Gondwana margin in the Late Cretaceous (as described below) fostered the development of endemic centers of marked faunal provincialism by the Paleocene Epoch (a total of >515 Southern Hemisphere Paleocene taxa recorded), as reflected in the dominance of new species in new genera, ranging in values from


62.5% to 81%, and many groups arising in this region for the first time (Stilwell, 2003; see review therein of entire Paleocene record of molluscs in New Zealand and Chatham Islands in this paper and not repeated here). These early Paleogene molluscan assemblages exhibit distinct (and sometimes dramatic) sig- natures of composition and biodiversity levels relating to


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extinction and post-extinction recovery processes, with a much richer record being recognized since the dawn of the new millennium. The composition of early Paleogene Mollusca reflects the


K-Pg boundary extinctions 66Ma as a major mechanism of change, which was more buffered in the southern high latitudes with increased survivorship relative to the Northern Hemisphere (Stilwell, 2003; Stilwell et al., 2004, Stilwell and Håkansson, 2012), in association with the final break-up of Gondwana and ensuing changes in oceanic circulation, and last, but not least, significant changes in climate at the boundary and shortly thereafter. One of the most important aspects of the changes in molluscan composition is the recognition of a major ‘flip-flop’ in diversity of Bivalvia and Gastropoda before and after the boundary 66Ma with gastropods diversifying greatly after the catastrophe in the ecologic vacuum of much vacant ecospace. The post-K-Pg molluscan record in Zealandia was one of


increasing endemism with the isolation of the region from the Gondwanan margin. During the mid- to late Paleocene the endemic component of the fauna was stronger at this time relative to any other during the entire Cenozoic with bivalve and gastropod genera at a level of endemicity of approximately 30%. As such, the paleoaustral component of the fauna was unsurprisingly high at 51% for bivalves and approximatel 68% for gastropods (Stilwell, 2003). Despite being at the tail end of


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