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The last global extinction (Mid-Pleistocene) of deep sea benthic foraminifera (Chrysalogoniidae, Ellipsoidinidae, Glandulonodosariidae, Plectofrondiculariidae, Pleurostomellidae, Stilostomellidae), their Late Cretaceous-Cenozoic history and taxonomy
Part 1. The Last Global Extinction in the Deep Sea During the Last Global Extinction (LGE) c. 20% (30 genera, 105 species) of cosmopolitan, mainly deep-sea (600–4000 m), benthic foraminiferal species (excluding unilocular taxa), belonging to seven families, became extinct. During this late Pliocene–middle Pleistocene interval (3.6–0.13 Ma), five families (Chrysalogoniidae, Glandulonodosariidae, Stilostomellidae, Ellipsoidinidae, Pleurostomellidae) were wiped out and one more (Plectofrondiculariidae) was almost wiped out with just one species surviving to the present. Most (76 of 105 species) of these extinctions occurred during the mid-Pleistocene Climate Transition (MPT, 1.2–0.55 Ma) at an extinction rate of 25% myr-1 of the deep-sea benthic foraminifera, compared with a background rate through the Cenozoic of c. 2% myr-1. Most species in the families Chrysalogoniidae, Stilostomellidae, Ellipsoidinidae and Pleurostomellidae had equal levels of abundance throughout their middle bathyal–middle abyssal depth ranges. The Glandulonodosariidae mostly lived at middle bathyal to uppermost abyssal depths and the Plectofrondiculariidae at bathyal to outer shelf depths. These Extinction Group (Ext. Gp) families comprised 30–70% of the deep-sea benthic foraminiferal fauna in the middle to late Eocene. Major declines in their relative abundance and species richness at abyssal depths began in the late Oligocene–Miocene in the Southern Ocean, in the late Miocene in the deep Indian Ocean, in the early Pliocene in the West Pacific, then globally in the late Pliocene at upper abyssal (2300–3000 m) depths and all depths in the Mediterranean Sea. At bathyal depths (900–2200 m) declines and extinctions were largely confined to the Pleistocene. These declines occurred in pulses mostly coinciding with glacial episodes of expansion of polar ice sheets, initially in Antarctica but during the MPT in the Arctic. The LGE preferentially impacted species with specific morphologies (elongate, cylindrical, often uniserial tests) and apertural types (e.g., small rounded, dentate, cribrate, or lunate slit). The precise functions of these are not known but the apertural modifications could be related to having a specific food source whose pulsed decline in abundance in the plankton resulted in the LGE. Data on δ13C analyses suggest that Ext. Gp species lived infaunally. Strong positive correlation of Ext. Gp abundance in the Pliocene–MPT with foraminiferal proxies for sustained and pulsed organic carbon flux supports the hypothesis that the Ext. Gp favoured enhanced food supply with consequent lower oxygen concentrations. Decreased bottom temperature, increased bottom water ventilation or carbonate corrosiveness, increased interspecific competition and predation, or increased or more wildly fluctuating food supply are all rejected as unlikely to be the causes of the LGE. We hypothesise that the cause may have been the progressive decline or demise of the specific phytoplankton source of the detritus that the Ext. Gp fed upon, during global cooling and later increasingly cold glacials of the MPT with lowered atmospheric CO2. The LGE and regional highest occurrence levels of Ext. Gp species have considerable biostratigraphic value in providing rapid age assessments of Quaternary oceanic sediment where planktic foraminiferal age datums are rare. Part 2. Late Cretaceous–Cenozoic History of the Extinction Group The absolute abundance and flux of the Ext. Gp were generally greater at bathyal than at deeper abyssal depths and in more eutrophic rather than oligotrophic regions. Peak Ext. Gp fluxes, relative abundance and species richness occurred between the middle Eocene and early Miocene but some short abundance peaks in the Pliocene–MPT were associated with brief periods of locally high productivity. The oldest Ext. Gp species originated in the Jurassic and eight more appeared in the Early Cretaceous. The peak of Ext. Gp species originations (2.7% myr-1) was Late Cretaceous, except in the Glandulonodosariidae (Paleocene) and Plectofrondiculariidae (middle to late Eocene). A secondary peak of originations (2% myr-1) occurred in the late Eocene across all Ext. Gp families. More than 80% of Ext. Gp species originated during the Cretaceous–Eocene (Greenhouse World) compared with c. 30% of modern deep-sea benthic foraminifera. The Cretaceous–Cenozoic Ext. Gp species had an even spread of species durations between five and 85 myrs (except plectofrondiculariids), with mean species durations of 50 myrs (Pleurostomellidae), 47 myrs (Glandulonodosariidae), 46 myrs (Stilostomellidae), 44 myrs (Ellipsoidinidae), 41 myrs (Chrysalogoniidae) and 20 myrs (Plectofrondiculariidae). Cenozoic Ext. Gp faunas are dominated by mostly long-lived species of just three genera – Strictocostella, Siphonodosaria and Pleurostomella. The Ext. Gp was largely unaffected by the K/Pg or PETM extinction events. The late Eocene–Oligocene cooling was the first interval where the Ext. Gp showed an above background level of faunal change or instability and species turnover (1% myr-1, esp. Ellipsoidinidae, Plectofrondiculariidae, Glandulonodosariidae). After an early Miocene decline, extinctions began accelerating in the middle to late Miocene (1% myr-1) concurrent with progressive cooling of mid and high latitude climate and surface waters. During the Middle Miocene Climate Transition, Ext. Gp relative abundance declined and some local changes in assemblage composition occurred, but there was no pulse in global species turnover. The rate of extinctions accelerated further in the Pliocene (3% myr-1, dominantly stilostomellids), accompanied by significant changes in the composition of the dominant and overall Ext. Gp fauna as they became less diverse. With one exception, the remaining 40% of the total Cretaceous–Cenozoic diversity of the Ext. Gp disappeared during the Pleistocene, mainly during the MPT. Part 3. Taxonomy of the Extinction Group Two hundred and fifty-three species from 38 genera in the Extinction Group families (Chrysalogoniidae, Glandulonodosariidae, Plectofrondiculariidae, Stilostomellidae, Ellipsoidinidae, Pleurostomellidae, Nodosariidae in part), are reviewed and illustrated, together with eight additional species that became extinct or declined dramatically during the Last Global Extinction. Twelve genera and 26 species are described as new (Anastomosa n.gen., A. boomgaarti n.sp., A. loeblichi n.sp., Cribroconica n.gen., Epelistoma n.gen., E. morgansi n.sp., Lotostomoides n.gen., L. jorisseni n.sp., L. schwageri n.sp., Scallopostoma n.gen., Glandulonodosaria colomi n.sp., G. lutzei n.sp., Fingerina n.gen., Grigelis schoenfeldi n.sp., Mucronina hornibrooki n.sp., M. resigae n.sp., Plectolingulina n.gen., Carchariostomoides n.gen., Caveastomella n.gen., C. caralpae n.sp., C. weinholzi n.sp., Siphonodosaria campana n.sp., S. kaihoi n.sp., S. robertsoni n.sp., Stilostomella? guptai n.sp., Strictocostella srinivasani n.sp., S. strongi n.sp., Toddostomella n.gen., Unidens n.gen., U. ishizakii n.sp., Ellipsoglandulina keyzeri n.sp., Ellipsoidella tappanae n.sp., Laterohiatus n.gen., Nodosarella kohli n.sp., N. nomurai n.sp., N. schroederadamsae n.sp., Obesopleurostomella n.gen., O. boltovskoyi n.sp., Ossaggittia n.gen., O. thomasae n.sp.). Three-hundred and seventy-three species and 20 genera are suppressed as subjective junior synonyms.