Radiolarian faunal turnover across the Oligocene/Miocene boundary in the equatorial Pacific Ocean

The global warming trend of the latest Oligocene was interrupted by several cooling events associated with Antarctic glaciations. These cooling events affected surface water productivity and plankton assemblages. Well-preserved radiolarians were obtained from upper Oligocene to lower Miocene sediments at Ocean Drilling Program (ODP) Leg 199 Sites 1218 and 1219 in the equatorial Pacific, and 110 radiolarian species were identified.Four episodes of significant radiolarian faunal changes were identified: middle late Oligocene (27.5 to 27.3 Ma), latest Oligocene (24.4 Ma), earliest Miocene (23.3 Ma), and middle early Miocene (21.6 Ma). These four episodes approximately coincide with increases and decreases of biogenic silica accumulation rates and increases in δ¹⁸O values coded as “Oi” and “Mi” events. These data indicate that Antarctic glaciations were associated with change of siliceous sedimentation patterns and faunal changes in the equatorial Pacific.Radiolarian fauna was divided into three assemblages based on variations in radiolarian productivity, species richness and the composition of dominant species: a late Oligocene assemblage (27.6 to 24.4 Ma), a transitional assemblage (24.4 to 23.3 Ma) and an early Miocene assemblage (23.3 to 21.2 Ma). The late Oligocene assemblage is characterized by relatively high productivity, low species richness and four dominant species of Tholospyris anthophora, Stichocorys subligata, Lophocyrtis nomas and Lithelius spp. The transitional assemblage represents relatively low values of productivity and species richness, and consists of three dominant species of T. anthophora, S. subligata and L. nomas. The characteristics of the early Miocene assemblage are relatively low productivity, but high species richness. The two dominant species present in this assemblage are T. anthophora and Cyrtocapsella tetrapera. The most significant faunal turnover of radiolarians is marked at the boundary between the transitional/early Miocene assemblages.We also reviewed changes in other microfossil assemblages in the low latitudes during the late Oligocene through early Miocene. The microfossil assemblages of major groups show sequential changes near the Oligocene/Miocene (O/M) boundary (23.8 Ma). Many extinction events and some first occurrences of calcareous nannofossils and many occurrences of radiolarians are found from about 24.8 to 23.3 Ma, and first occurrences of planktic foraminifers and diatoms followed from 23.2 through 22 Ma. Hence, the O/M boundary is identified as a significant level for microfossil evolutions.     

Equatorial Pacific sea surface temperatures, faunal patterns, and carbonate burial during the Pliocene

A high-resolution record of radiolarian faunal abundances from the eastern equatorial Pacific is compared to records of carbonate and noncarbonate burial to examine the evolution of eastern tropical Pacific climate processes during the Pliocene. These data provide a means to evaluate the sensitivity of the equatorial Pacific to the onset of Northern Hemisphere glaciation around 2.8−2.5 Ma, to the closure of the Isthmus of Panama around 4.4−3.2 Ma, and to orogeny-related weathering changes before 4.0 Ma. Radiolarian faunal assemblages and sea surface temperature (SST) estimates indicate a gradual cooling from early to late Pliocene, but no significant changes occur near the onset of northern hemisphere glaciation. Records of carbonate and noncarbonate mass accumulation show a long term decrease from the Miocene/Pliocene boundary to the upper Pliocene. Greater carbonate burial in the early Pliocene relative to the late Pliocene parallels a gradual cooling from early to late Pliocene, and may reflect changes related to Isthmus closure or widespread orogeny. No significant time domain changes are seen in the eastern equatorial Pacific that could be related to the onset of Northern Hemisphere glaciation.Evolutive spectral analyses of these equatorial Pacific climate parameters indicate that variance in SST and seasonality commonly concentrate at frequencies not linearly related to orbital variations. Furthermore, cross spectral comparisons with a high resolution benthic δ¹⁸O record indicate that the surface ocean and carbonate flux share little coherent variance with high latitude climate processes during the Pliocene. Given the high degree of chronostratigraphic control in these records, these results suggest that Milankovitch-band surface ocean processes as well as carbonate burial in the equatorial Pacific are decoupled from high latitude climate processes during the Pliocene.     

塔斯曼海南部更新世放射虫的生物地层学

本研究利用保存丰富、完好的放射虫对塔斯曼海更新世层序进行地层学分析。对塔斯曼海南部更新世的KH94-4TSP-4PC岩芯的放射虫组合进行了详细的生物地层学分析,并从8 .6 m长的岩芯中识别出83种放射虫。依据放射虫属种的出现和消失,可得到两个放射虫带,即Chi带(老)和Psi带(新)。Chi带的顶部以Saturnalis cir-culariHaeckel ,Cycladophora pliocenicaHays的最后出现和Triceraspyris antarcticaHaecker的首次出现为标志。Psi带的顶部以Stylatractus universusHay和Antarctissa cylindricaPetrushevskaya的最后出现为标志。这些放射虫带可与浮游生物的有孔虫Globorotalia ( G.) truncatulinoides带进行对比。     

Miocene biochronology and paleoceanography of the North Pacific

Biostratigraphic correlation based on microfossil datum levels, directly or indirectly tied to the paleomagnetic time scale, provides a high resolution time control for the Miocene in the equatorial and middle latitude North Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen isotope record of foraminifers, reveal the paleoclimatic and paleoceanographic history. The planktic foraminiferal assemblage change in the early Miocene, extinction of Oligocene fauna and rise of a highly diverse Neogene fauna, appears to be related to increased water mass stratification in the world oceans presumably resulting from the establishment of circum-Antarctic circulation. An increase in the siliceous productivity in the eastern equatorial Pacific region between 20 and 18 Ma suggests that the vertical and horizontal circulation was intensified at that time. Climates cooled rapidly during the middle Miocene between 14 and 13 Ma suggesting the growth of a major east Antarctic ice sheet. Paleoclimatic conditions remained generally cool, although oscillating, during the late Miocene. In the late early to middle Miocene faunal provincialism developed between low and middle latitudes, and by late Miocene time a distinct provincialism similar to the present was established.     

Regional patterns of evolutionary turnover in Neogene coral reefs from the central Indo-West Pacific Ocean

The Indo-Pacific is an area of intense ecological interest, not least because of the region’s rich biodiversity. Important insights into the origins, evolutionary history, and maintenance of Indo-Pacific reef faunas depend upon the analysis of faunal occurrences derived from detailed stratigraphic sections. We investigated Neogene origination and extinction patterns derived from a combination of new coral occurrences and previously published records from the central Indo-West Pacific Ocean (cIWP, Indonesia, Papua New Guinea and Fiji). Two faunal turnover events were observed. In the first, an increase in generic richness of Scleractinia from the cIWP during the middle Miocene (17–14 Ma) coincided with both large-scale sea level fluctuations and the great Mid-Miocene collision event. We raise the hypothesis that Mid-Miocene origination was facilitated by habitat and population fragmentation associated with tectonism and sea level fall. The second, subsequent, turnover event was characterized by an overall lowering of generic diversity throughout the late Miocene and Pliocene (7–3 Ma), and was followed by a pronounced pulse of extinction at the Pliocene–Pleistocene boundary (~2.6 Ma). With the exception of the onset of Pleistocene sea-level cycles and the onset of northern hemisphere glaciation around 2.5 Ma, which might explain increased extinction during this time interval, there are no tectonic, eustatic, climatic or oceanographic events that neatly coincide with this second episode of Neogene coral taxonomic turnover. Our results reveal a total of 62 genera, including synonyms, from the Miocene to the Pleistocene. Neither episode of turnover among coral genera is exactly coincident with turnover in the Atlantic thus regional environmental change is found to drive Neogene reef dynamics.     

Permian and Triassic Radiolaria from Northwest Thailand: paleogeographical implications

Well-preserved radiolarians were recovered from seven sections in the Mae Hong Son-Mae Sariang area, northwestern Thailand. 51 species assigned to 34 genera are identified, including 1 new species (Triassospongosphaera erici Feng sp. nov.) and 19 unidentified species. They are divided into the Late Permian, late Ladinian and middle Carnian radiolarian assemblages. Newly identified radiolarian assemblages, together with the published radiolarian biostratigraphic data from this region, indicate that there was a pelagic basin during the Late Paleozoic and Triassic. This basin was joined to the Chiang Dao and Changning-Menglian oceanic basins, and they represent the main oceanic basin of the Paleotethyan Archipelago Ocean. This main oceanic basin was situated in the traditional “Shan-Thai Block”. Therefore, “the Shan-Thai Block” was not a single block during that stage, but composed of the Paleotethyan Ocean and two continental terranes that were affiliated with the Gondwana and Cathaysian domains, respectively.     

Sea-surface temperature changes in the North Pacific during the Late Miocene

Twenty-seven radiolarian species and species groups are identified and used in this study. Their stratigraphic ranges span from Late Miocene to modern times and they appear to have distributions which have changed little over this interval of time. Census data for these 27 taxa in surface sediment samples are used to define six assemblages (Q-mode factors). The distribution of these assemblages are similar to modern water-mass distributions and can be statistically related to modern sea-surface temperatures.Census data on these same 27 taxa have been collected in the Upper Miocene intervals of six Pacific sites. These faunal data are described in terms of the modern radiolarian assemblages; and based on the multiple regression equations relating the modern assemblages to modern temperatures, estimates of Late Miocene temperatures are made. The estimated temperatures indicate that there is an overall cooling trend in the later part of the Miocene (magnetic Chron 8 to Chron 5), punctuated by several distinct cooling events. In August the low-latitude sites appear to be slightly cooler, and the mid-latitude sites warmer than in modern times. In February both the low- and mid-latitude sites appear to be warmer than modern temperatures at the same locations. The relatively warm temperatures near the base of the interval studied may be associated with the passage of warm tropical Atlantic waters into the eastern Pacific via the Isthmus of Panama. The general cooling trend seen in these records is thought to be associated with the gradual closure of these straits and the increased influence of the high southern latitudes.     

Late Miocene—early Pliocene planktonic foraminiferal biostratigraphy and paleoceanography of low-latitude marine sequences

Plate reorganization and development of polar glaciation are closely associated with the changing climatic conditions of the Cenozoic. The planktonic foraminiferal fauna in three low-latitude DSDP sites (224, Ninety East Ridge; 317B, Manihiki Plateau; 366A, Sierra Leone Rise) has been examined to determine how these regions responded to the late Miocene climatic cooling that has been previously observed in high-latitude regions. It has been proposed that an expansion of Antarctic glaciation and a resultant eustatic regression are associated with this cooling, with the latter being at least partially responsible for the Messinian “salinity crisis” in the Mediterranean.Only one of the sites, 366A, shows any significant faunal change during the late Miocene and early Pliocene (approximately 8-3 Ma). During the late Miocene, there is a decrease in the abundance of species considered to be tropical-subtropical, suggesting the incursion of a cool water mass into the Sierra Leone Rise region during this time. The lack of any major faunal changes at Sites 214 and 317B indicates that the water masses of the low-latitude regions of the Indo-Pacific were relatively unaffected by this cooling in the late Miocene.The three sites also show no evidence for a change in the level of the CCD between the late Miocene and early Pliocene; however, this is most likely due to their equatorial position and shallow water depth. Higher-latitude sites from both the Atlantic and the Pacific reveal a definite shoaling of the CCD during the late Miocene.     

Late neogene biostratigraphy and stable isotope stratigraphy of a drilled core from the Gulf of Mexico

Late Neogene stable isotope stratigraphy and planktonic foraminiferal biostratigraphy have been examined in a high sedimentation rate core (E67-135, Shell Oil Co.) drilled at 725 m water depth in the De Soto Canyon, Gulf of Mexico. The 305 m core contains sections that are Late Miocene, Early Pliocene, Late Pliocene, and Quaternary in age, and is rich in well-preserved assemblages of planktonic foraminifera.A biostratigraphy has been established based on the ranges of 34 selected species of foraminifera. The core 3orrelates with sections from the Gulf of Mexico, the Caribbean Sea, and the subtropical North and South Atlantic Oceans using, as datums, the evolutionary appearances of Globorotalia miocenica Palmer and Globorotalia margaritae evoluta Cita, the extinction of Globorotalia miocenica and the first appearance of Globorotalia truncatulinoides (d'Orbigny).Oxygen and carbon isotope stratigraphy is based on analysis of the benthonic foraminifer, Uvigerina d'Orbigny. Isotopic trends are similar to those observed in the Pacific and Atlantic Oceans. From Early Pliocene to Late Pleistocene time, average δ¹⁸O values increase (2.42‰ to 3.36‰) and exhibit a wider range of values (0.71‰ in Early Pliocene compared to 1.65‰ in Late Pleistocene sediments), probably reflecting Late Neogene climatic deterioration. The ratio ${}^{13}\text{C}{}^{12}\text{C}$ decreases significantly by ?0.21‰ from the Late Miocene to the Early Pliocene. A decrease in δ¹³C is observed in other cores and is probably related to changing oceanic circulation patterns in Late Miocene time.     

Late Quaternary history of atmospheric and oceanic circulation in the eastern equatorial Pacific

Four radiolarian assemblages have been defined in recent seafloor sediments of the equatorial Pacific Ocean. The distribution of these assemblages corresponds to the modern pattern of oceanic circulation and water mass structure in this region: the eastern Pacific shallow permanent thermocline and the Equatorial Undercurrent; Peru Current upwelling and the oxygen minimum; the subtropical water mass; warm western tropical water and the North Equatorial Countercurrent. In twelve cores chosen to transect the region both longitudinally and latitudinally, the distribution of these four assemblages has been reconstructed for six time-intervals during the last 127,000 years: 18,000 B.P. (glacial Stage 2); 36,000 B.P. and 52,000 B.P. (interstadial Stage 3); 65,000 B.P. (glacial Stage 4); 82,000 B.P. and 120,000 B.P. (interglacial Stage 5). Atmospheric and oceanic circulation changes through time have been inferred from the reconstructed microfossil assemblage distributions. Changes in assemblage distributions indicate that variations in intensity, direction and mean position of the tradewinds caused marked changes in the oceanic circulation patterns through the last glacial cycle.Near the end of interglacial Stage 5, the disappearance of the North Equatorial Countercurrent from the eastern Pacific suggests that the mean position of the tradewinds was shifted to the south approximately 5° of latitude relative to the modern position, so that the Northeast trades prevented the flow of the North Equatorial Countercurrent into the eastern Pacific. Near the end of interstadial Stage 3, a change in wind direction occurred from predominantly zonal winds, which enhance equatorial divergence and surfacing of the Equatorial Undercurrent, to more meridional winds, which enhance coastal upwelling associated with the Peru Current.In the tropical Pacific Ocean, late Quaternary changes in atmospheric and oceanic circulation are linked with times of continental ice sheet growth in the Northern Hemisphere (i.e., the interglacial-to-glacial transitions across oxygen isotope stage boundaries $\text{5}\text{4}$ and $\text{3}\text{2}$). The major changes in circulation seem to occur a few thousand years in advance of the glacial episodes, at or near periods of ice sheet growth. This relationship indicates that changes in atmospheric circulation in the tropics led and influenced the development of conditions suitable for polar and continental ice sheet growth in the Northern Hemisphere.     

Ancient Divergence in the Trans-Oceanic Deep-Sea Shark Centroscymnus crepidater

Unravelling the genetic structure and phylogeographic patterns of deep-sea sharks is particularly challenging given the inherent difficulty in obtaining samples. The deep-sea shark Centroscymnus crepidater is a medium-sized benthopelagic species that exhibits a circumglobal distribution occurring both in the Atlantic and Indo-Pacific Oceans. Contrary to the wealth of phylogeographic studies focused on coastal sharks, the genetic structure of bathyal species remains largely unexplored. We used a fragment of the mitochondrial DNA control region, and microsatellite data, to examine genetic structure in C. crepidater collected from the Atlantic Ocean, Tasman Sea, and southern Pacific Ocean (Chatham Rise). Two deeply divergent (3.1%) mtDNA clades were recovered, with one clade including both Atlantic and Pacific specimens, and the other composed of Atlantic samples with a single specimen from the Pacific (Chatham Rise). Bayesian analyses estimated this splitting in the Miocene at about 15 million years ago. The ancestral C. crepidater lineage was probably widely distributed in the Atlantic and Indo-Pacific Oceans. The oceanic cooling observed during the Miocene due to an Antarctic glaciation and the Tethys closure caused changes in environmental conditions that presumably restricted gene flow between basins. Fluctuations in food resources in the Southern Ocean might have promoted the dispersal of C. crepidater throughout the northern Atlantic where habitat conditions were more suitable during the Miocene. The significant genetic structure revealed by microsatellite data suggests the existence of present-day barriers to gene flow between the Atlantic and Pacific populations most likely due to the influence of the Agulhas Current retroflection on prey movements.     

Pleistocene fish otoliths from the Mediterranean Basin: a synthesis

An overview of upper pPliocene and pleistocene otolith assemblages is compiled on the basis of both literature data and newly collected material from several sections located mainly in southern Italy. One hundred and five taxa are listed. Additional comments are provided for taxa subject to discussion. The composition and affinities of the Mediterranean Pleistocene otolith associations (consisting mainly of deep sea fishes) is checked against the available data for Pre-Messinian, Pliocene, and Recent Mediterranean fishes. This analysis is based on the recorded nominal species, but some taxa that could be identified at the generic level only are also included when they are relevant from a biogeographic point of view. Some new data on Piacenzian (middle Pliocene) and Gelasian (upper Pliocene) otoliths are also provided because this time interval still constitutes a major gap in the knowledge of the stratigraphic range of Plio-Pleistocene fish taxa. The Pleistocene deepwater fish fauna of the Mediterranean shows a markedly more oceanic character than the present-day one, a tendency that was all ready observed from early Oligocene till Pliocene times. Starting from the late Piacenzian, an increasing number of Atlantic taxa progressively invaded the Mediterranean including several subpolar and temperate forms. This invasion became stronger in the Gelasian. From this period up to the middle and late Pleistocene, the Mediterranean deepwater fish fauna (mesopelagic and benthopelagic) is enriched by taxa which today are typical for the north Atlantic cold deep water. This faunal shift seems to be correlated with the evolution of the Plio-Pleistocene Mediterranean paleoceanographic setting as well as with the global climatic deterioration.     

Fish otoliths from the pre-evaporitic (Early Messinian) sediments of northern Italy: their stratigraphic and palaeobiogeographic significance

The study of otolith assemblages from the pre-evaporitic Messinian deposits allows the reconstruction of a fauna of 79 taxa of which 35 could be identified at the specific level. Three of these are new: Diaphus rubus, Myctophum coppa, and Uranoscopus ciabatta. The assemblages reflect mainly a neritic environment influenced by the oceanic realm. Analysis of the global present-day geographic distribution of 42 of the recognised Messinian genera indicates that 88% of these are still living in the Mediterranean, 98% in the Atlantic and 78% in the Indo-Pacific realm. These results are in good agreement with the evolutionary trends documented for the Oligocene and Miocene teleost fauna, specifically an increase in percentage of genera inhabiting the modern Mediterranean, a very high percentage of Atlantic and Indo-Pacific genera, and a slight fall of the importance of present-day Indo-Pacific genera from the Rupelian up to the Late Miocene. Analysing the composition of the Early Messinian fauna at the level of nominal species indicates that about 53% of the species represented in the assemblages are still living in the Recent Mediterranean, and that a significant number of these were already present in the Tortonian. It is interesting that these species are mainly neritic. This seems to confirm that the close affinity of the fossil assemblage with the present-day Mediterranean neritic fauna, which was already recorded at the genus level for the Rupelian fauna, persists during the Neogene and continues until the Pleistocene.     

Late Pleistocene molluscan assemblages from the coral reefs of the Kenya coast

Since the Last Interglacial, there have been profound changes in the nature of the fringing reef along the Kenya coast. These are most apparent in the back-reef region where a marked decline in habitat diversity has led to a significant reduction in the variety of molluscan assemblages. Despite dramatic changes in the composition of these assemblages, very few species have become extinct. The four late Pleistocene species apparently missing from the Recent fauna of the Kenya coast still occur further east in the Indonesia-West Pacific region. There is evidence to suggest that range retractions from the periphery to the core region occurred at the same time in other parts of the Indo-Pacific province too. The province's margins may well have been more susceptible to fluctuations in certain environmental parameters, such as temperature, during the Pleistocene climatic cycles.     

Radiolarian assemblages in surface sediments along longitude 175°E in the Pacific Ocean

This study of 24 surface sediment samples along longitude 175°E between latitudes 48°N and 14°S in the western Pacific Ocean documents the relationship between the modern distribution of radiolarian assemblages and present oceanographic conditions. Ninety-two species were classified into eight clusters by using R-mode cluster analysis. Q-mode cluster analysis was used to distinguish five geographical zones, which were interpreted to represent the Tropical, Southern Subtropical, Northern Subtropical, Transitional, and Subarctic climatic zones. Species richness, diversity, and equitability are highest in the Tropical and Transitional Zones. We attempted to formulate new regression equations considering ecological information on the vertical distribution of radiolarian species. Transfer functions were derived from regression analysis of radiolarian assemblages to observed Sea Surface Temperature (SST) values. The transfer functions have a standard error of 1.16 °C in the estimate of winter SST, 0.81 °C in that of summer SST.     

Biostratigraphic and paleoclimatic significance of a new Pliocene foraminiferal fauna from the central Arctic Ocean

A Pliocene benthic foraminiferal fauna containing a previously unknown species association was found in the basal section of a piston core collected from the crest of Northwind Ridge (NWR) in the central Arctic Ocean. The fauna is dominated by Epistominella exigua, Cassidulina reniforme, Eponides tumidulus, Cibicides scaldisiensis, Lagena spp., Cassidulina teretis, Eponides weddellensis, Bolivina arctica, and Patellina corrugata. The presence of Cibicides scaldisiensis in the assemblage and the occurrence of Cibicides grossus higher in the core are indicative of an early Pliocene age. The morphologically distinctive species Cibicidoides sp. 795 of McNeil (in press) which occurs in the NWR core sample was previously known only from Oligocene through Miocene deposits in the Beaufort-Mackenzie Basin of Arctic Canada. Ehrenbergina sp. A and Cibicidoides aff. C. sp. 795, also present in the core, are new and endemic to the Arctic late Miocene and early Pliocene. These species, and possibly others, are survivors of the late Miocene (Messinian) sea-level crisis, which caused a significant faunal turnover in the Arctic Ocean. The predominantly calcareous assemblage indicates deposition above the calcium carbonate compensation depth in an upper bathyal environment. Paleogeographic affinities for the bulk of the assemblage indicate probable connections between the Arctic and the North Atlantic Oceans, but the endemic species identify environmental differences or partial isolation of the western Arctic Ocean. The species association suggests a cold but milder paleoclimate than that which existed during Pleistocene glacial intervals.     

Distribution of living polycystine radiolarians in the Gulf of Mexico and Caribbean Sea,and comparison with the sedimentary record

Plankton tows and bottom samples from the Gulf of Mexico and Caribbean Sea were examined to study the distribution, ecology, and preservation of modern radiolarians. Abundances of radiolarians from this region, an area of low primary productivity, are low. Diversities are variable in the surface waters; diversity indices decrease with increasing water depth, indicating that fewer niches are occupied by radiolarians in deep water. Living radiolarians are confined to specific water masses, some species ranging between two masses, and can be used as indicators of these water masses in ecologic or paleo-oceanographic studies.The record of radiolarian tests present in the sediment is dissimilar to the record of living radiolarians in the water column, but is similar to the record of empty tests falling through the water column. This indicates that a considerable length of time is involved in the settling of radiolarian tests. It also confirms the validity of ecologic interpretations based on a study of sediments only.     

Tethyan changes shaped aquatic diversification

The Tethys Ocean existed between the continents of Gondwana and Laurasia from the Triassic to the Pliocene. Analyses of multiple biogeographic and phylogenetic histories reveal that the subsequent breakup of the Tethys greatly influenced the distributions of many species. The ancestral Tethyan realm broke into five biogeographic provinces, including the present‐day East Pacific, West Atlantic, East Atlantic, Mediterranean Sea, and Indo‐West Pacific. Palaeogeographic maps illustrate the Mesozoic Atlantic opening, the Cenozoic closure of the Tethys, the Messinian Salinity Crisis, the mid‐Miocene closure of the Central American Seaway, and Quaternary geological changes. Further, we consider Cenozoic sea‐level changes and the formation of freshwater habitats. These reconstructions allow assessment of patterns of aquatic diversification for marine and freshwater animals, and comparison of vicariance and dispersal processes. Estimated divergence times indicate that fragmentation of the Tethys was responsible for the vicariant speciation of aquatic animals because these dates are consistent with associated tectonic events. The opening of the Atlantic Ocean during the Cretaceous is responsible for the earliest isolation between the West and East Atlantic. The mid‐Miocene closure of the Tethys, which blocked global equatorial currents, appears to have isolated the Atlantic/Mediterranean Sea and Indo‐West Pacific. Finally, formation of the Isthmus of Panama isolated East Pacific and West Atlantic marine organisms. Dispersals related to the Messinian Salinity Crisis and Quaternary sea‐level changes influenced population structuring. Tethyan changes affected marine habitats, created new freshwater habitats, inland caves and ancient lakes along the Alps and Himalayas, and influenced anchialine caves at the edge of the ancient sea. The extensive new habitats provided opportunities for colonisation and rapid diversification. Future work should focus on testing the biological impact of the series of Tethyan changes.     

Influences of past climatic changes on historical population structure and demography of a cosmopolitan marine predator,the common dolphin (genus Delphinus)

Climatic oscillations during the Pleistocene have greatly influenced the distribution and connectivity of many organisms, leading to extinctions but also generating biodiversity. While the effects of such changes have been extensively studied in the terrestrial environment, studies focusing on the marine realm are still scarce. Here we used sequence data from one mitochondrial and five nuclear loci to assess the potential influence of Pleistocene climatic changes on the phylogeography and demographic history of a cosmopolitan marine predator, the common dolphin (genus Delphinus). Population samples representing the three major morphotypes of Delphinus were obtained from 10 oceanic regions. Our results suggest that short‐beaked common dolphins are likely to have originated in the eastern Indo‐Pacific Ocean during the Pleistocene and expanded into the Atlantic Ocean through the Indian Ocean. On the other hand, long‐beaked common dolphins appear to have evolved more recently and independently in several oceans. Our results also suggest that short‐beaked common dolphins had recurrent demographic expansions concomitant with changes in sea surface temperature during the Pleistocene and its associated increases in resource availability, which differed between the North Atlantic and Pacific Ocean basins. By proposing how past environmental changes had an effect on the demography and speciation of a widely distributed marine mammal, we highlight the impacts that climate change may have on the distribution and abundance of marine predators and its ecological consequences for marine ecosystems.     

Change in diversity,ecological significance and biogeographical relationships of the Mediterranean Miocene toothed whale fauna

The main evolutionary trend in the Mediterranean Miocene toothed whale fauna is related (1) to the change in diversity and (2) to the turnover in community structure. Diversity increases from Upper Aquitanian–Lower Burdigalian to Burdigalian–Langhian, when it reaches its maximum. Starting from this time, diversity decreases progressively. The Early Miocene (Upper Aquitanian–Lower Burdigalian) Mediterranean toothed whale fauna, as well as the extramediterranean ones, is characterised by a high number of endemic taxa and by the prevalence of longirostral forms living in estuarine-neritic environments. A more diversified fauna spreading in neritic and pelagic environments characterises the Burdigalian–Langhian age, while an increase in pelagic forms and the nearly complete disappearance of some archaic longirostral taxa is typical of the Serravallian–Messinian fauna. Decrease in diversity and disappearance of archaic longirostral taxa are also recorded, at more general scale, in the Late Miocene extramediterranean fossil bearing deposits. These events can be related to the progressive global climatic deterioration, starting from Middle Miocene. From a biogeographic point a view, we can outline some relationships between the Mediterranean and western North Atlantic Miocene faunas. Closer affinities are observed between the Baltringen fauna and the northern Atlantic one, because of the presence of the genera Pomatodelphis and Zarhachis (platanistids) in both areas. In the Miocene Mediterranean and in North Atlantic, the delphinids are apparently absent as well as other extant delphinoid groups even if erroneously recorded in the past.