Jeffrey D. Stilwell

Patterns of biodiversity and faunal rebound following the K–T boundary extinction event in Austral Palaeocene molluscan faunas

Palaeocene molluscan faunas are characterised by complex evolutionary histories following the Cretaceous–Tertiary (K–T) boundary extinction event and exhibit dramatic, distinct signatures of composition and biodiversity levels relating to extinction and post-extinction recovery processes. This paper is the first to document and survey the entire Palaeocene record of the Southern Hemisphere, which comprises at least 515 recorded molluscan taxa from Australia, New Zealand/Chatham Islands, Antarctica, and South America. The record is much richer than previously recognised. The K–T boundary event was a prime mechanism of change for the composition of Palaeocene faunas, but Palaeocene diversity patterns were shaped also by the final break-up of Gondwana, concomitant changes in climate and in oceanic circulation, and faunal recovery processes. The ‘flip-flop’ in diversity of bivalves and gastropods across the K–T boundary stems from a rapid, evolutionary burst of speciation in the Danian for gastropods, especially carnivorous forms with planktotrophic development, which infilled ecospace vacated by the extinction. In the Southern Hemisphere fossil record, deposit feeders were less affected by the extinction event and seemingly more extinction-resistant, but other important factors related to stratigraphic range and spectrum of life habits/habitats affected survivorship success. Suspension feeders, especially epifaunal forms, were hard hit by the extinction, but had bounced back within a few million years by late Danian time at the latest, but at lower diversity than during the Late Cretaceous. The extinction was not as marked in most southern regions, as reflected in the Antarctic record. In the Antarctic K–T boundary interval, diversity drops suddenly ca 50 m before the boundary, and while suspension feeders remain at low diversity for at least 300 kyr, gastropods still dominate the molluscan assemblages. Most of the K–T boundary molluscan survivors were bivalve species (66%) and all of these were members of representative genera that displayed extensive stratigraphic and geographic ranges in the Cretaceous or earlier in the Mesozoic. The majority of earliest Danian Antarctic molluscs belong to newly evolved species within surviving genera (58%), but by late Danian time this trend had changed to a dominance of new species in new genera. Many new groups arose during the Palaeocene, especially by late Danian time, and these faunas are highly distinctive at both genus and species level. For example, the Wangaloa Formation fauna of late Danian age (ca 63–61 Ma) is dominated by new species in new genera, ranging in values from 62.5 to 81%. A systematic catalogue of all known Palaeocene Austral species is presented herein in the Appendix for the first time with details of formation recorded, age, and inferred life habits.

Tectonic and palaeobiogeographic significance of the Chatham Islands, South Pacific, Late Cretaceous fauna

Abstract The Cretaceous fauna of the Chatham Islands, South Pacific, is essentially a tectonically controlled facies fauna, with origins relating to divergent plate motions and concomitant deposition of volcaniclastic, transgressive sediments in half-grabens in the Chatham Rise region during the Late Cretaceous. At least 60 macroinvertebrate (predominantly Mollusca) taxa and one vertebrate have been recorded from the Kahuitara Tuff (Campanian-lower Maastrichtian) of Pitt Island. The separation of the New Zealand subcontinent, including the Chatham Rise and Tasman Sea region, from the Marie Byrd Land sector of the Gondwana margin, along with changing oceanic circulation, lowering sea-surface temperatures and believed increasing temperature gradients, enhanced the distinctiveness of the fauna, as reflected in the strong species-level endemicity of the fossil record. Shoaling from volcanic activity in the Chatham Islands region created substrates suitable for colonization of a characteristic hardground community dominated by epifaunal suspension feeders (ca. 41%), followed by lower percentages of infaunal suspension feeders (ca. 30%), epifaunal browsers (ca. 14%), deposit feeders (ca. 8%), and carnivores (ca. 5%). The Kahuitara Tuff faunule is divided into four biogeographic groupings at genus- and subgenus-level: Indo-Pacific/Tethyan (ca. 37%), cosmopolitan (ca. 34%), palaeoaustral (ca. 28.5%), and endemic (ca. 8.5%). Palaeoaustral taxa are inclusive of endemic groups, in accordance with C.A. Flemings original ideas. These percentages suggest an overall relatively warm-water, semi-global biogeographic flavour at this taxonomic level. Some 43% of taxa from the Kahuitara Tuff are found in mainland New Zealand coeval faunas and about 41% are endemic to the Chatham Islands, differences being attributable largely to facies and to a much lesser degree to geographic isolation. At species level, endemic taxa of cosmopolitan or wide-ranging Indo-Pacific/Tethyan and palaeoaustral genera/subgenera (83%) dominate, with negligible representation of widespread or cosmopolitan species and endemic species of endemic genera/subgenera. It is suggested that the Kahuitara Tuff faunule represents evolutionary divergence, reflecting range retractions of a former cosmopolitan, early to late Mesozoic world. Nearly all Kahuitara Tuff taxa are endemic to either the Chatham Islands or mainland New Zealand. Similarities of the fauna with other coeval faunas around the rim of the southern circum-Pacific are moderate to weak at genus- and subgenus-level, indicating a degree of provincialism and isolation, especially at species level. The Chatham Islands fauna probably belonged to the short-lived, Campanian to Masstrichtian, Weddellian Biotic Province of W.J. Zinsmeister. The Kahuitara Tuff fauna evolved from a mixture of Austral and Boreal elements during the Late Cretaceous with evidence of approximately 40% taxa having ancestors in the Chatham Islands-New Zealand region of the Gondwana supercontinent. Changes in composition across the Kue5f8T boundary in the Chatham Islands were dramatic with very few genus- and subgenus-level taxa in the Kahuitara Tuff present in the Upper Palaeocene to Lower Eocene Red Bluff Tuff.

On the rare occurrence of Eocene callianassid decapods (Arthropoda) preserved in their burrows, Mount Discovery, East Antarctica

Callianassid fossils, preserved within their burrows, collected from Mount Discovery, East Antarctica, provide the first such occurrence in Antarctica as well as evidence for deposition in a shallow marine environmental distal to a deltaic system. The age of the specimens, based upon associated dinoflagellate cysts, is late early to middle Eocene.

Late Cretaceous Mollusca from the Chatham Islands, New Zealand

The Cretaceous Mollusca (Bivalvia, Gastropoda, Scaphopoda) from the Chatham Islands, New Zealand consists of a moderately diverse faunule of 37 species in the Kahuitara Tuff of Pitt Island. At least 16 (c.43%) of the taxa are conspecific with mainland New Zealand species and at least 15 (c.41%) taxa are endemic to Chatham Islands. New species proposed are Crenella n. sp., Chlamys (Lyriochlamys) n. sp., Chlamys s. l. n. sp., Camptonectes n. sp., Eburneopecten freneixae n. sp., Dimyodon n. sp., Purpurocardia n. sp., Lahillia n. sp., Solyma flemingae n. sp., Brookula s. l. n. sp., Calliomphalus s. l. n. sp., Pyrgulifera kahuitara n. sp., and Ageria? n. sp. Most taxa (c.41%) are epifaunal suspension feeding bivalves and dominate the Cretaceous macrofauna. Less dominant are infaunal suspension feeding bivalves (30%). Epifaunal browsers (c.14%), deposit feeders (8%) and carnivores (5%) are minor components. An open marine, shallow shelf environment is advocated. A latest Cretaceous (Campanian?-Maastrichtian) ag...

DESCRIPTION AND PALEOBIOGEOGRAPHIC SIGNIFICANCE OF A RARE CENOMANIAN MOLLUSCAN FAUNULE FROM BATHURST ISLAND, NORTHERN AUSTRALIA

Abstract A middle Cenomanian faunule from the Moonkinu Formation of Bathurst Island in Northern Australia contains the best-preserved suite of benthic Mollusca known from the Cretaceous of the Australian region. Twenty-four species of bivalves, gastropods, and scaphopods, many exquisitely preserved with original aragonitic nacre, are recognized. Thirteen are new: Nucula s.l. meadinga n. sp. (Nuculidae), Nuculana bathurstensis n. sp. (Nuculanidae), Jupiteria? n. sp. A (Nuculanidae), Varicorbula cretaustrina n. sp. (Corbulidae), Vanikoropsis demipleurus n. sp. (Vanikoridae), Euspira n. sp. A (Naticidae), Amuletum praeturriformis n. sp. (Turridae), Granosolarium cretasteum n. sp. (Architectonicidae), Echinimathilda moonkinua n. sp. (Mathildidae), Acteon bathurstensis n. sp. (Acteonidae), Biplica antichthona n. sp. (Ringiculidae), Goniocylichna australocylindricata n. sp. (Cylichnidae), and Dentalium (Dentalium) n. sp. A (Dentaliidae). Nominal species of Nuculana, Grammatodon, Cylichna, and Laevidentalium also are present. The occurrence of ammonites, including taxa that occur in the type Cenomanian, securely establishes the fauna as middle Cenomanian (Acanthoceras rhotomagense Zone). The Moonkinu Formation and its faunule were deposited in a high-energy, shallow-shelfal setting, as part of a large-scale regressive cycle recognized as the Money Shoals Platform of northern Australia. The assemblage represents a parauthochthonous suite which experienced little or no post mortem transport. Epifaunal and infaunal suspension feeders (some 60 percent) dominate the bivalve fauna with a subordinate representation of deposit-feeding infaunal burrowers (some 40 percent). Nearly all of the gastopods were carnivores with the aporrhaid Latiala mountnorrisi (Skwarko), probably a deposit feeder, the only exception. The scaphopods were probably micro-carnivores. Concentrations of the ammonite Sciponoceras glaessneri are likely the result of mass kills in surface waters. The cosmopolitan nature of the Bathurst Island fauna at the genus-level reflects unrestricted oceanic circulation patterns and an equitable climate on a global scale during the Cenomanian. The retreat and disappearance of the Australian epicontinental sea at the close of the Albian coincided with reduced endemism in the molluscan faunas, after which time the continental shelves hosted a rich suite of cosmopolitan affinity. The high number of endemic species in the Moonkinu Formation probably represents an early stage of broad-scale genetic separation among Southern Hemisphere molluscan stocks, a trend that became increasingly pronounced through the Late Cretaceous. The new records of Varicorbula, Amuletum, Granosolarium, Echinimathilda, and Goniocylichna represent the oldest occurrences recorded for these genera and are suggestive of Southern Hemisphere origins.

Diversity, distribution, and evolutionary history of the Austral, Late Cretaceous to Eocene, gastropod Struthioptera (Stromboidea: Aporrhaidae)

Abstract The prominently alate and sculptured marine gastropod, Struthioptera (Caenogastropoda: Stromboidea: Aporrhaidae) appeared in the New Zealand region at the latest during the early Cenomanian (early Late Cretaceous). Struthioptera campiveta n. sp., from the Marlborough region, is the first member and likely progenitor of the group, but no potential ancestor to Struthioptera has been recovered from Lower Cretaceous rocks. Concomitantly with the final separation of the Gondwana fragments in the latest Cretaceous, species‐level diversity of Struthioptera climbed and the group diverged into at least four coeval species by this time: S. haastiana in the New Zealand region; S. novoseelandica in both New Zealand and Chatham Islands; S. pastorei in southern Argentina, Patagonia; and S. smiti in the Antarctic Peninsula region. Struthioptera? protuberatus from the Late Cretaceous of Patagonia may also belong here. The Cretaceous‐Tertiary (K‐T) boundary extinction crisis reduced the genus to a single representative, S. osiris, in the early Danian (late Early Paleocene) in New Zealand, and its probable descendant, S. camachoi, from the Middle‐Late Eocene of Antarctic Peninsula. Shell size in Struthioptera increased markedly over the K‐T boundary and the group became extinct in the Late Eocene, probably as a result of marked temperature changes near the Eocene/Oligocene boundary. Presented here is the first detailed review of Struthioptera since the first specimen was collected at Wangaloa, South Island, New Zealand, in late 1868 or early 1869. Species of Struthioptera are inferred to have been epifaunal and/or semi‐infaunal deposit feeders and rather gregarious marine snails in sandy facies along the shallow shelf.

Cretaceous Scaphopoda (Mollusca) of Australia and their palaeobiogeographic significance

The Cretaceous scaphopod (molluscan) fauna of mainland Australia is characterised by a rather depauperate and poorly known assemblage of five species: dentaliids Dentalium (Dentalium) n. sp. A (probably Aptian), Dentalium (Dentalium) n. sp. B (Cenomanian), and Dentalium (Dentalium) n. sp. C (Maastrichtian); fustiariid Fustiaria wollumbillaensis (Etheridge, Jr., 1892) (Late Aptian-Albian?); and laevidentaliid Laevidentalium cretaustralium n. sp. (Late Albian). Each species is endemic to either the Great Artesian Basin or Carnarvon Basin of Australia. A probable sixth species is recorded from Cenomanian deposits of Bathurst Island, but the affinity of this taxon is uncertain. In some shell beds of the Allaru Formation, scaphopods dominate the preserved macrobenthos. Although at species level the fauna is endemic, strongly cosmopolitan genus level links of the scaphopods mirror that of other groups of molluscs (bivalves, gastropods, cephalopods), indicating derivation from evolutionary separation from pre-ex...

A NEW, LARGE ACTEONID GASTROPOD (MOLLUSCA) FROM THE LATEST CRETACEOUS OF ANTARCTICA

Opisthobranch gastropods are rare in Mesozoic deposits of Antarctica. The first documented occurrence of opisthobranchs from this continent is from Cretaceous shallow-marine deposits of the James Ross Basin, Antarctic Peninsula, where Wilckens (1910, p. 95–96, pl. 4, fig. 19) described the minute ringiculid Cinulia sp., based on five specimens from two localities on Snow Hill Island. No further work has been done on the Snow Hill Island species. The next mention of Antarctic Cretaceous opisthobranchs was by Zinsmeister et al. (1989, p. 733, fig. 2, p. 734, fig. 3), who cited the occurrence of the ringiculid “ Oligoptycha cf. O. concinna Meek and Hayden, 1858,” in the lowermost part of Unit 8 of the Lopez de Bertodano Formation (Maastrichtian) on the southern half of Seymour Island (Fig. 1). We report the first record of Acteonidae from the Mesozoic of Antarctica, Acteon (Tenuiactaeon) antarctihadrum n. sp., discovered in shallow-marine Maastrichtian deposits.nnnnFigure 1 —Index map of Seymour Island, Antarctic Peninsula, showing the distribution of Maastrichtian and Danian strata on the southern two-thirds of the island. Diagonal hatched, Lopez de Bertodano Formation. The numbers correspond to Macellaris lithologic units (1–5, Upper Campanian; 6–9, Maastrichtian, and 10, Danian). Cross hatched, Sobral Formation; Stippled region, Cross Valley Formation, Late Paleocene; Unshaded northern region of Seymour Island, Eocene La Meseta Formation. Diagonal black lines crossing the Sobral and units 8 through 10 of the Lopez de Bertodano Formations represent a Neogene dike complex. Thick lines between units 9 and 10 represent the K-T boundary. Locality 1620 is 692 m above the base of the sequence (dip of strata 8 degrees)nnnnSeymour Island provides an exceptionally rich and well-preserved fossil record across the Cretaceous-Tertiary (K-T) boundary. The diverse suites of molluscs from this small Antarctic isle offer important insight on the composition …

Unusual belemnite — incoceramid bivalve association from the Albian (late Early Cretaceous) of Queensland, Australia

An unusual occurrence in the upper Albian Toolebuc Formation of Queensland, Australia, of penetration of a guard of the belemnite Dimitobelus (Dimitobelus) stimulus into the disc of an indeterminate inoceramid bivalve, is the first report of this type of shell damage in the fossil record. The belemnite punctured completely both valves of the bivalve to the maximum diameter of the belemnite guard, by inferred compaction from sediment overburden during post-mortem biostratinomic processes. Shell thickening of the inoceramid bivalve by shearing of prismatic layers at the site of puncture indicates that the bivalve shell behaved plastically during the puncture and that the great flexibility of the prismatic layers was facilitated by the relatively thin shell and presence of organic sheaths around individual prisms. This flexibility may have been advantageous during a predatory attack, by allowing the maintenance of a seal during breakage of the shell margin.

A new gastropod mollusc, Antarctissitys austrodema gen. et sp. Nov., from the upper Maastrichtian of Antarctica and its evolutionary significance

The Maastrichtian Lopez de Bertodano Formation of Seymour Island, Antarctic Peninsula, hosts the most diverse assemblage of Late Cretaceous molluscs from the continent. Described here is a new genus and species of gastropod, Antarctissitys austrodema gen. et sp. nov., from the upper units of the formation, which are inferred to represent a mid-shelf clastic environment. Antarctissitys austrodema is assignable to the Perissityidae (Muricoidea) and is the first confirmed record of this family in the Southern Hemisphere, indicating a much more widespread Cretaceous geographic distribution. Fusus dusenianus Wilckens from the Upper Cretaceous of Patagonia and Perissitys? sp. from the Maastrichtian of New Zealand may also belong in Perissityidae, but preservational deficiencies prevent any firm assessment. The affinities of Antarctissitys gen. nov. lie with a diverse suite of perissityid taxa in the Upper Cretaceous of North America, belonging predominantly to Perissitys.