Deep-sea benthonic foraminiferal faunal turnover near the Eocene/Oligocene boundary

Eocene-Oligocene deep-sea benthonic foraminifera in D.S.D.P. Site 277 in the southwest Pacific have been analyzed to determine the benthonic foraminiferal response to the development of the psychrosphere near the Eocene/Oligocene boundary. Biostratigraphic ranges of 41 taxa show that 23 taxa are found throughout the Late Eocene to Early Oligocene sequence, while 18 taxa exhibit first or last occurrences. Comparison of the faunal changes in Site 277 with a benthonic foraminiferal oxygen isotope record shows that the development of the psychrosphere did not have a profound effect upon the benthonic foraminifera, and the overall faunal change preceding and subsequent to the bottom-water circulation event occurred gradually. The inferred water-mass event affected the relative abundance of one species, Epistominella umbonifera. The lack of major faunal changes at the Eocene/Oligocene boundary in Site 277 probably reflects either wide environmental tolerances of the benthonic foraminifera, or a bottom-water temperature change less than 3°C.Examination of previously published benthonic foraminiferal biostratigraphic data from D.S.D.P. Sites 167, 171, 357, 360, 363, and 400A, and deep-sea ostracode data from D.S.D.P. Leg 3 show faunal changes occurred during discrete intervals in the Middle Eocene-Early Oligocene. The faunal patterns from these data and from Site 277 show that the Eocene/Oligocene cooling event did not cause rapid, catastrophic changes of the benthonic faunas of the open ocean, although significant faunal changes are associated with the water mass event in Sites 167, 171 and 400A.The benthonic faunal changes in Middle Eocene-Early Oligocene time are consistent with the gradual decrease of inferred bottom-water temperatures, based on previously published oxygen isotopic data. The δ ¹⁸O Eocene/Oligocene enrichment of 0.76‰ is a major event in the Southern Ocean oxygen isotopic record, but is considerably less in magnitude than the 1.75-2.00‰ change that occurred gradually from mid-Early Eocene to the Eocene/Oligocene boundary. The benthonic foraminiferal and isotopic data indicate that bottom-water circulation may have developed during the Middle Eocene to Early Oligocene interval, with the 3°C bottom-water cooling near the Eocene/Oligocene boundary representing part of this development.     

Scolecophidia (Serpentes) of the Late Oligocene and Early Miocene,North America,and a fossil history overview

An abundant fossil record of the snake clade Scolecophidia exists in Europe; however, the minute snake is noticeably absent in reports about the North American Paleogene and Neogene. Presented here are four localities from Florida, USA, that contain scolecophidian remains older than the Pleistocene: Thomas Farm (late Early Miocene, Hemingfordian Land Mammal Age, LMA), Live Oak (Oligocene-Miocene transition, latest Arikareean LMA), White Springs 3B (late Arikareean LMA), and Brooksville 2 (Late Oligocene, middle Arikareean LMA). These remains extend their known existence by about 26 m.y. and are now the oldest reported scolecophidian remains in North America. Molecular evidence on extant scolecophidians concludes that these tiny snakes have a Gondwanan origin. Interestingly, the oldest record of a scolecophidian is from Europe (Belgium) and dates back to the middle Paleocene (MP 1–5). The earliest African record of the snake clade comes from the Paleocene-Eocene boundary in Morocco. The clade is apparently absent from Europe and Middle East deposits dating from the latest Eocene through to the latest Oligocene (MP 19–30) and to the Early Miocene (MN 4). A portion of this time is known as the booid ‘Dark Period’ which represents an apparent response to global aridization and cooling. Scolecophidians appear to re-emerge into the southern Eurasian record in the Early Miocene (MN 4) and become widely dispersed throughout Europe and Middle East. The fossil record of these minute snakes is largely absent in southern Asia and South America. It is possible that the current lack of a decent fossil scolecophidian record outside of Europe and Middle East is due mainly to a bias in the methodology to recover fossils; wet sieving sediments through < 1.0 mm mesh is needed to recover the minuscule vertebrae.     

Shallow-marine ostracode faunas around the Eocene/Oligocene boundary in the northwestern Kyushu, southwestern Japan

Middle Eocene–early Oligocene ostracode faunal changes in northwestern Kyushu of southwestern Japan are identified in this study. Ostracodes occur from shelf deposits of five formations: the middle Eocene Okinoshima, the upper Eocene Funazu, the uppermost Eocene–lowermost Oligocene Kishima, the lowermost Oligocene Itanoura, and the lower Oligocene Waita Formations. The middle Eocene–earliest Oligocene ostracodes were characterized by warm-water genera, indicating tropical, subtropical and Tethyan genera, whereas the late early Oligocene ostracodes do not include warm-water taxa, consisting of temperate realm genera. The middle Eocene–earliest Oligocene ostracodes do not include remarkable changes of species composition, in contract with equatorial Pacific radiolarians and West Coast USA molluscs. Ostracodes suggest that distinct climatic cooling did not occur in the southwestern Japan during the middle Eocene–earliest Oligocene.     

Battenizyga, a new Early Triassic gastropod genus with a discussion of the caenogastropod evolution at the Permian/Triassic boundary

Battenizyga, a new Early Triassic gastropod genus from the Moenkopi Formation of Utah, is described and the speciesAnoptychia eotriassica Batten & Stokes, 1986 is placed in it. The new genus has an axially ribbed planktonic larval shell and a teleoconch with an angulated periphery. This character combination is unknown from the Palaeozoic. Therefore,Battenizyga represents additional evidence that recovery from the end-Permian mass extinction was connected with a faunal turnover. Additionally, the extinction of diverse Palaeozoic groups of the Caenogastropoda in the Permian (e.g., the Pseudozygopleuridae) suggest a turnover. All caenogastropod genera that hold Early Triassic species, have post-Palaeozoic type species and most were not reported from the Palaeozoic. This corroborates the view that there was an intense faunal turnover within the Caenogastropoda.Battenizyga is probably a caenogastropod that is closely related to the superfamily Zygopleuroidea which is abundant in the late Palaeozoic and early Mesozoic.      

Sedimentary and faunal changes across the frasnian/famennian boundary in the canning basin of Western Australia

The Canning Basin of northwestern Australia is a key area for understanding global changes at the “Kellwasser Events” and the Frasnian‐Famennian boundary. Frasnian stromatoporoid‐coral‐cyanobacterial reef platforms stretched out for enormous distances along the palaeoshelf but in the early Famennian they were completely replaced by cyanobacterial reef platforms. An iridium anomaly in the sequence was formerly believed to be at or close to the boundary and was interpreted as possible evidence for an asteroid impact. Recent field work and detailed biostratigraphy in the area east and southeast of Fitzroy Crossing has given dating relevant to the timing and extent of sea level changes, hypoxic incursions and reef backstepping. Goniatites and conodonts provide correlations with the international biostratigraphy.

In the Horse Spring area the stage boundary falls within the Virgin Hills Formation which normally has a rich pelagic goniatite, nautiloid and conodont fauna. In the latest Frasnian (Zone 13 of Klapper 1989; regional Sphaeromanticoceras lindneri Zone) large allochthonous reef blocks moved downslope into the open marine basin. A diverse gastropod fauna is associated with the last atrypid brachiopods. The faunal record at the immediate boundary is obscured by dolomitisation but manticoceratid goniatites range into this level. There is no evidence for the organic‐rich dark Kellwasser limestone facies.

In the McWhae Ridge area two Frasnian goniatite horizons with Beloceras trilobites and the giant Mamicoceras guppyi and Sphaeromanticoceras lindneri transgress over the reef slope. Stromatolitic cyanobacterial beds mark condensations. Again there is no trace of the oxygen‐depleted Kellwasser facies. However, as at Horse Spring, manticoceratids persisted into dolomitic marker beds that have no other preserved macrofauna. The iridium anomaly associated with Frutexites postdates the Frasnian‐Famennian boundary and was formed by cyanobacterial concentration.     

Benthic foraminiferal turnover across the Cretaceous/Paleogene boundary at Agost (southeastern Spain): paleoenvironmental inferences

We studied Upper Cretaceous and Lower Paleogene benthic foraminifera from the Agost section (southeastern Spain) to infer paleobathymetrical changes and paleoenvironmental turnover across the Cretaceous/Paleogene (K/P) transition. Benthic foraminifera indicate uppermost bathyal depths at Agost during the Abathomphalus mayaroensis Biochron (from about 400 kyr before the K/P boundary) through the early Plummerita hantkeninoides Biochron (about 120–150 kyr before that boundary). The depth increased to middle bathyal for the remainder of the Cretaceous, and remained so for the Danian part of the studied section (Parasubbotina pseudobulloides Biochron, at least 200 kyr after the K/P boundary). There were no perceivable bathymetrical changes at the K/P boundary, where 5% of the species became extinct, and the species composition of the benthic foraminiferal fauna changed considerably. Below the boundary, infaunal morphogroups constitute up to 65–73% of the faunas. Directly above the boundary, in the black clays of the lower Guembelitria cretacea Biozone, benthic foraminifera are rare. Several opportunistic taxa (e.g. the agglutinant Haplophragmoides sp.) have short peaks in relative abundance, possibly reflecting low-oxygen conditions as well as environmental instability, with benthos receiving food from short-lived, local blooms of primary producers. Above the clays through the end of the studied interval, epifaunal morphogroups dominate (up to 70% of the assemblages) or there is an even mixture or epifaunal and infaunal morphogroups. Infaunal groups do not recover to pre-extinction relative abundances, indicating that the food supply to the benthos did not recover fully over the studied interval (about 200 kyr after the K/P boundary). The benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact, which severely destabilized primary producers and the oceanic food web that was dependent upon them.     

Causes of perceived faunal change in the later Neogene of East Africa

African terrestrial vertebrate faunas change over the time range from 14 my to 4 my, the period during which hominids are presumed to have diverged from other hominoids. The most complete local sequence showing this is provided by the Tugen Hills, west of Lake Baringo in Kenya. A large component of the pattern of faunal changes seen there, and at other relevant sites, could be explained by local environmental alterations, or by sampling properties of fossil assemblages and collections. It is hard to justify global climatic change as the sole explanation of observed faunal shifts, although such external factors cannot be ruled out and on general grounds are likely to be involved. As yet there is no convincing demonstration of synchronicity in faunal turnover. Evidence of a simple shift from forest conditions to grasslands, an event that has been correlated with the origins of hominid bipedalism, is hard to detect. Existing data suggest a more patchy distribution of forest and grassland in both space and time.     

Mammalian turnover and community structure in the Paleocene of North America

The effects of faunal turnover on mammalian community structure are evaluated for 17 faunal zones of the North American Paleocene through early Eocene land mammal ages (Puercan through early Wasatchian). Generic disappearances were significantly high at the end of the Puercan, Torrejonian, and Tiffanian land mammal ages, but appearances were significantly high only during the early Puercan. Generic richness rose rapidly in the early Puercan, remained stable throughout most of the Paleocene, and increased from the late Paleocene into the early Eocene. The null hypothesis that generic turnover clustered preferentially according to dentally defined trophic or body size categories could be rejected or attributed to sampling problems for all but the early (Pu0) and late Paleocene (Ti5‐Cf2). Early Paleocene change in community structure most probably represented endemic radiation of mammals into previously unoccupied niches. Community restructuring in the late Paleocene reflected a complex of causes, including climatic wanning, intercontinental dispersal, and competition.     

New dyrosaurid crocodylomorph and evidences for faunal turnover at the K-P transition in Brazil

The discovery of a new dyrosaurid crocodylomorph from the well-dated Palaeocene deposits of northeastern Brazil sheds new light on the evolutionary history of this extinct group of marine crocodylomorphs that have survived the Cretaceous-Palaeogene (K-P) extinction crisis. Guarinisuchus munizi, the most complete member of this group collected in South America so far, is closely related to the African forms, and this fact suggests that dyrosaurids had crossed the Atlantic Ocean before the K-P boundary and dispersed from there to North America and other parts of South America. This discovery also suggests that on the coast of northeastern Brazil, dyrosaurids replaced the pre-existing Late Cretaceous fauna of diversified mosasaurs, a group of marine lizards, after the K-P extinction event, becoming the main predators, together with sharks, in shallow marine Palaeocene environments. More detailed stratigraphic records and detailed dating of the deposits with dyrosaurids are necessary to correlate this particular pattern found in the ancient northeastern Brazilian coast within the evolution of the group, especially in Africa.     

Food supply to the seafloor in the Pacific Ocean after the Cretaceous/Paleogene boundary event

Deep-sea benthic foraminifera show important but transient assemblage changes at the Cretaceous/Paleogene (K/Pg) boundary, when many biota suffered severe extinction. We quantitatively analyzed benthic foraminiferal assemblages from lower bathyal–upper abyssal (1500–2000 m) northwest Pacific ODP Site 1210 (Shatsky Rise) and compared the results with published data on assemblages at lower bathyal (~ 1500 m) Pacific DSDP Site 465 (Hess Rise) to gain insight in paleoecological and paleoenvironmental changes at that time.At both sites, diversity and heterogeneity rapidly decreased across the K/Pg boundary, then recovered. Species assemblages at both sites show a similar pattern of turnover from the uppermost Maastrichtian into the lowermost Danian: 1) The relative abundance of buliminids (indicative of a generally high food supply) increases towards the uppermost Cretaceous, and peaks rapidly just above the K/Pg boundary, coeval with a peak in benthic foraminiferal accumulation rate (BFAR), a proxy for food supply. 2) A peak in relative abundance of Stensioeina beccariiformis, a cosmopolitan form generally more common at the middle than at the lower bathyal sites, occurs just above the buliminid peak. 3) The relative abundance of Nuttallides truempyi, a more oligotrophic form, decreases at the boundary, then increases above the peak in Stensioeina beccariiformis. The food supply to the deep sea in the Pacific Ocean thus apparently increased rather than decreased in the earliest Danian. The low benthic diversity during a time of high food supply indicates a stressed environment. This stress might have been caused by reorganization of the planktic ecosystem: primary producer niches vacated by the mass extinction of calcifying nannoplankton may have been rapidly (<10 kyr) filled by other, possibly opportunistic, primary producers, leading to delivery of another type of food, and/or irregular food delivery through a succession of opportunistic blooms.The deep-sea benthic foraminiferal data thus are in strong disagreement with the widely accepted hypothesis that the global deep-sea floor became severely food-depleted following the K/Pg extinction due to the mass extinction of primary producers (“Strangelove Ocean Model”) or to the collapse of the biotic pump (“Living Ocean Model”).     

Neoselachian (Chondrichthyes, Elasmobranchii) diversity across the Cretaceous-Tertiary boundary

Fishes are often thought to have passed through mass extinctions, including the Cretaceous-Tertiary (KT) event, relatively unscathed. We show that neoselachian sharks suffered a major extinction at the K/T boundary. Out of 41 families, 7 became extinct (17±12%). The proportional measure increases at lower taxic levels: 56±10% loss of genera (loss of 60 out of 107) and 84±5% loss of species (loss of 182 out of 216). However, the Maastrichtian and Danian are characterized by a high number of singleton taxa. Excluding singletons we have calculated a 34±11% loss of genera and a 45±9% loss of species. The simple completeness metric (SCM) for genera displays a decrease from the Maastrichtian (94%) to the Danian (85%) indicating a rather complete fossil record of neoselachian genera. The extinctions were heavy among both sharks and batoids (skates and rays), but most severe among batoids, which lost almost all identifiable species. There were equal losses among open marine apex predators (loss of Anacoracidae, Cretoxyrhinidae, and Scapanorhynchidae) and durophagous demersal forms from the continental shelf and shallow seas (Hypsobatidae, Parapaleobatidae, Sclerorhynchidae, Rhombodontidae). Benthopelagic and deep-sea forms were apparently little affected. New families with similar ecological roles (Carcharhinidae, Isuridae, Torpedinidae) replaced these families in the Danian, and full diversity of the different shark and batoid groups had been recovered by the end of the Paleocene or early Eocene. Sharks and rays suffered levels of extinction entirely in line with other groups of organisms at the K/T extinction event.     

Carnivores from the early/middle Miocene locality of Antonios (Chalkidiki, Macedonia, Greece)

The mammal locality of Antonios is one of the few known early-middle Miocene ones of Greece with large mammals. It is situated in Chalkidiki Peninsula (Macedonia, Greece) and includes both small and large mammals. The study of the carnivores found in Antonios indicates the presence of the following taxa: Proputorius cf. P. sansaniensis, Protictitherium gaillardi, Protictitherium cf. P. crassum, Percrocuta sp., Percrocutidae indet. and Pseusaelurus romieviensis. The material of each taxon is described, compared with other material from various Eurasian localities and determined. The species P. cf. sansaniensis and P. romieviensis are traced for first time in Eastern Mediterranean, while Percrocuta for first time in Greece. The presence of the other carnivoran taxa in the Antonios fauna is also interesting as they are recognized in older stratigraphic levels enriching our knowledge about their stratigraphic distribution. The carnivores of Antonios cannot offer significant data for the dating of the fauna but its age is discussed using the data coming from the carnivores as well as those from older studies of the micromammals and suoids.     

First discovery of the Miocene northern Atlantic sperm whale Orycterocetus in the Mediterranean

An incomplete mandible of a fossil sperm whale (Odontoceti; Physeteridae) is described. It is a portion of elongated and narrow symphysis with cylindrical and slightly curved teeth without enamel. The specimen, collected from the Miocene “Pietra leccese” sediments of South Italy, appears to represent a species of Orycterocetus, and is the first such record from the Mediterranean. Considering the wide diffusion of Orycterocetus in the North Atlantic, we believe its rare presence in the Mediterranean as occasional and due to a certain degree of interchange between the Mediterranean and the North Atlantic cetacean fauna during the Miocene.     

Role of planktonic bacteria in productivity and cycling of organic matter in the Eastern Pacific Ocean

Total number, biomass, production, and respiration of bacterioplankton were measured in oligotrophic, mesotrophic and eutrophic waters of the Eastern Pacific. Total number of bacteria in the upper mixed layer and in the upper thermocline boundary layers varied from 30–60.10³ ml^-1 in oligotrophic waters to 100–400.10³ ml^-1 in mesotrophic waters of fronts and divergences, and to 1–2,5.10⁶ ml^-1 in eutrophic waters of coastal upwellings. Wet biomass varied from 5–10 mg l^-1 in oligotrophic waters, to 50–200 mg l^-1 in mesotrophic waters, and to 1–2 g m^-3 in eutrophic waters. Below the layer of maximum temperature gradient i.e. below 35–50 m, bacterioplankton density decreased 5–10 times. P/B coefficients per day were highest in the oligotrophic surface water ( 1), and lowest in the eutrophic ones (0.2–0.4). In mesotrophic waters they were intermediate (0.4–1.0). the stock of labile organic matter (LOM) accessible to microbial action varied from 0.3 to 1.6 mg Cl^-1. Its highest value occurred in the upwelling area. The stock of LOM does not noticeably decrease from the euphotic zone to a depth of 2 000 m. Its turnover time varied from 5 to 45 days in surface waters, and 30–50 years in deep oceanic waters. The role of bacterioplankton in productivity and in cycling of organic matter in surface — and deep oceanic waters is discussed.     

Dental evolution in Neophanomys (Rodentia, Octodontidae) from the late Miocene of central Argentina

The evolutionary pattern of the molar morphology of the small caviomorph (Octodontidae) Neophanomys from the late Miocene Cerro Azul Formation of central Argentina is analyzed. Two new species (chronomorphs) are recognized, which constitute an anagenetically evolving lineage with a gradual and directional pattern of increasing molar hypsodonty. Dental changes related to increasing hypsodonty are comparable to those of the octodontid lineage Chasichimys also recovered from the Cerro Azul Formation. However, Neophanomys shows comparatively less variation in gross morphology and there are no evidences that this lineage achieved euhypsodonty. In contrast, important changes in enamel microstructure (schmelzmuster) are observed among different populations of Neophanomys, supporting the hypothesis that these changes can occur at least partially independently from modifications in dental gross morphology. The patterns of dental evolution detected in the Neophanomys and Chasichimys-Xenodontomys lineages and the unequivocal polarity of the changes involved, related to increasing hypsodonty, reinforce the hypothesis that chronological differences exist among late Miocene outcroppings of Cerro Azul Formation in central Argentina.     

The Middle Miocene climatic transition in the Southern Ocean: Evidence of paleoclimatic and hydrographic changes at Kerguelen plateau from planktonic foraminifers and stable isotopes

Middle Miocene (14.8–11.9 Ma) deep-sea sediments from ODP Hole 747A (Kerguelen Plateau, southern Indian Ocean) contain abundant, well-preserved and diverse planktonic foraminiferal assemblages. A detailed study of the climatic and hydrographic changes that occurred in this region during the Middle Miocene Climatic Transition led to the identification of an intense cooling phase (the Middle Miocene Shift). Abundance fluctuations of planktonic foraminiferal species with different paleoclimatic affinities, and oxygen and carbon stable isotopes have been integrated in a multi-proxy approach. Reconstruction of changes in foraminiferal faunal composition and diversity through time were the basis for identification of three foraminiferal biofacies. The most prominent faunal change took place at 13.8 Ma, when a fauna with warm-water affinity (marked by high abundance of Globorotalia miozea group and Globoturborotalita woodi plexus) was replaced by an oligotypic, opportunistic fauna with typical polar characters and dominated by neogloboquadrinids. This faunal change is interpreted as the result of foraminiferal migration from adjacent bioprovinces, caused by modifications in climate and hydrography. A positive 2.0‰ shift in δ¹⁸O (interpreted as the Mi3 event) and a related positive 1.0‰ shift in δ¹³C (corresponding to the CM6 event) accompanied this faunal turnover. These are interpreted to reflect substantial reorganization of Southern Ocean waters, the northward migration of the Polar Front and a strong increase in primary productivity. The second faunal change took place at 12.9 Ma and was characterized by the gradual decrease in abundance of the neogloboquadrinids and the recovery of Globorotalia praescitula/scitula group and Globigerinita glutinata. A positive 1.5‰ shift in δ¹⁸O (interpreted as the Mi4 event) and a concurrent gradual negative shift in δ¹³C accompanied this faunal change, witnessing further modifications of the climate/ocean system. Variations in sea surface temperature, considered as the main factor causing changes of surface hydrography at the Kerguelen Plateau, seem to have been driven by obliquity and long-term eccentricity, thus suggesting a key role played by the astronomical forcing on the evolution of Southern Ocean dynamics during the Middle Miocene. Also an evident 1.2 Myr modulation of the δ¹³C record suggests a main control of the long-term obliquity cycles on the carbon cycle dynamics. Particularly, the Mi3/CM6 events exactly fit with a node of the 1.2 Myr modulation cycles. This confirms the key role played by orbital parameters on high-latitude temperatures and Antarctic ice volume, and indirectly on global carbon burial and/or productivity. This climatic transition was marked also by changes in surface hydrography. From 14.8 to 13.8 Ma an intermediate-strength thermocline controlled by seasonality developed just below the photic zone. Weaker seasonality characterized the interval from 13.8 to 12.9 Ma, when the thermocline became shallower and sharper and favored intermediate-water foraminifers. From 12.9 Ma, seasonality increased again and an intermediate-strength thermocline re-developed.     

Temporal changes in therophytic communities across the boundary of disturbed-intact ecosystems

External control processes cause continual compositional and structural readjustments of Mediterranean pasture ecosystems. Such control processes include herbivore grazing, meteorological fluctuations and traditional management activities, which determine the stable environment where the succession occurs. Traditional management in this ecosystem frequently involves periodic ploughing or controlled fires.Experimental disturbances were applied to pastures of different maturity. Recovery was studied by relating information gathered for each disturbed system to successional age. The boundary between original systems of differing ages and the newly created systems was studied to compare the space-time evolution of therophytic communities. Permanent transects perpendicular to the disturbance boundaries and containing many small plots were sampled during consecutive years.Sampling plots located on both sides of the boundaries were classified into communities, in order to detect the space-time pasture evolution in successive years. Annual conditional probabilities were calculated for transitions between the recognised communities. During succession different strategies were detected in response to meteorological variations. In pioneer successional stages, substitutions of one community by another in the same space seem to be random. However, greater determinism was detected in more mature pastures, where, in addition, communities' abundance does not respond to meteorological change.Nomenclature follows T. G. Tutin et al. 1964–1980. Flora Europaea. Cambridge University Press, Cambridge.     

Sea surface distribution of coccolithophores in the eastern Pacific sector of the Southern Ocean (Bellingshausen and Amundsen Seas) during the late austral summer of 2001

Horizontal distributions of coccolithophores were observed in sea surface water samples collected on the RV Polarstern between 27 February and 10 April, 2001, in the Pacific sector of the Southern Ocean (Bellingshausen and Amundsen Seas). These samples were analyzed to gain information about the distribution of coccolithophores in relation to the oceanic fronts of the Southern Ocean. A total of fifteen species of coccolithophores were identified, showing cell abundances of up to 67 × 10³ cells/l down to 63°S. Emiliania huxleyi was the most abundant taxon, always accounting for more than 85% of the assemblage. The second most abundant species was Calcidiscus leptoporus, with values lower than 7%. Cell density increases significantly in both the Subantarctic and Polar Fronts (155 and 151 × 10³ cells/l, respectively), decreasing abruptly in the intervening Polar Frontal Zone and to the south of the Polar Front. Although temperature at high latitudes is the main factor controlling the biogeographical distribution of coccolithophores, at the regional level (Southern Ocean) the frontal systems, and consequently nutrient distribution, play a crucial role.     

Comment on “The oldest South American Cricetidae (Rodentia) and Mustelidae (Carnivora): Late Miocene faunal turnover in central Argentina and the Great American Biotic Interchange” by D.H. Verzi and C.I. Montalvo [Palaeogeography, Palaeoclimatology, Palaeoecology 267 (2008) 284–291]

In a recent paper (Verzi, D.H., Montalvo, C.I., 2008. The oldest South American Cricetidae (Rodentia) and Mustelidae (Carnivora): late Miocene faunal turnover in central Argentina and the Great American Biotic Interchange. Palaeogeography, Palaeoclimatology, Palaeoecology 267, 284–291) the potentially oldest South American Cricetidae (Rodentia) and Mustelidae (Carnivora) have been reported from a Late Miocene (Huayquerian) assemblage located in central Argentina (Caleufú site, La Pampa province). These findings expand the biochron of these important families in South America 3–4 Ma earlier than previous records. However, several observations prevent us from accepting the validity of these assumptions. In this paper we discuss the age of the Caleufú assemblage, and the assignment of the GHUNLPam 21722 to Mustelidae. The Caleufú assemblage contains a mixture of Pliocene and Late Miocene faunal elements, and has been assigned to the Huayquerian only due to the “stage of evolution” of some rodents. The lack of isotopic or paleomagnetic data coupled with the isolation of this locality and the absence of a local stratigraphic succession inhibit its correlation with other palaeontological comparable sites and a robust inference about its chronology. The “stage of evolution” of a taxon is not a biostratigraphic tool, thus we cannot rule out the possibility that the Caleufú assemblage has an Early Pliocene (Montehermosan) age. The GHUNLPam 21722, a poorly preserved specimen, shows several characters (e.g., 4 lower incisors, mental foramina below the incisors absent, third lower incisor smaller than the first and second ones) that do not match with Mustelidae (or Carnivora) but instead strongly resemble those observed in didelphimorphian marsupials. The discussed caveats regarding Caleufu assemblage chronology and taxonomy indicate that new and detailed studies are needed before the hypotheses advanced by Verzi and Montalvo can be accepted.