Early Neogene Research Articles

Itaquaquecetuba Formation, São Paulo basin, Brazil: new angiosperm components of Paleogene Taphoflora

Among the various geological formations found in the State of Sao Paulo, the Itaquaquecetuba Formation, located in the Sao Paulo sedimentary basin, is one of the richest in Cenozoic plant fossils, allowing a detailed study of the flora which existed in that region, from the Paleogene to the Early Neogene. The plants identified in this formation, in general, belong to the families Melastomataceae and Fabaceae of the angiosperms group. In this study, one foliar impression of Leandra (Melastomataceae), being this the first fossil record of the genus, and one of Bauhinia (Fabaceae) were identified. These foliar fragments allowed us to observe in detail the leaf architecture and then to carry out the generic assignment. The form assigned to the genus Leandra resembles more the current species L. acutiflora and that assigned to the genus Bauhinia suggests affinity with B. divaricata. However, the ancient registration and the lack of an accuracy of the diagnostic characteristics lead us to use Leandra sp. and Bauhinia aff. B. divaricata designations. Some aspects of the paleogeography of both genera are discussed.

Diversity in neotropical wet forests during the Cenozoic is linked more to atmospheric CO 2 than temperature

Models generally predict a response in species richness to climate, but strong climate-diversity associations are seldom observed in long-term (more than 10(6) years) fossil records. Moreover, fossil studies rarely distinguish between the effects of atmospheric CO2 and temperature, which limits their ability to identify the causal controls on biodiversity. Plants are excellent organisms for testing climate-diversity hypotheses owing to their strong sensitivity to CO2, temperature and moisture. We find that pollen morphospecies richness in an angiosperm-dominated record from the Palaeogene and early Neogene (65-20 Ma) of Colombia and Venezuela correlates positively to CO2 much more strongly than to temperature (both tropical sea surface temperatures and estimates of global mean surface temperature). The weaker sensitivity to temperature may be due to reduced variance in long-term climate relative to in higher latitudes, or to the occurrence of lethal or sub-lethal temperatures during the warmest times of the Eocene. Physiological models predict that productivity should be the most sensitive to CO2 within the angiosperms, a prediction supported by our analyses if productivity is linked to species richness; however, evaluations of non-angiosperm assemblages are needed to more completely test this idea.

Greater past disparity and diversity hints at ancient migrations of European honey bee lineages into Africa and Asia

AbstractAimWe re‐evaluated the proposition based on the present‐day distribution of honey bees (genus Apis) that their centre of origin resides in Asia, with subsequent migration and diversification into Europe and Asia. In our research, we considered the so‐far largely ignored fossils distributed through a variety of late Palaeogene (Oligocene) and early Neogene (Miocene) deposits, aiming at a synthesis of both present‐day and past honey bee distribution.LocationNorthern Hemisphere, Africa, Southeast Asia.MethodsWe examined the morphological diversity (also termed ‘disparity’) and affinities of the full living and fossil diversity of honey bees ranging from their earliest origins to the present day. Based on the fossil record and present‐day distribution of species, considering continental drift from the Oligocene until today, we have established an evolution and migration scenario for the genus Apis.ResultsThe fossil record of Apis demonstrates a diversity that is predominantly European in origin, particularly among the most basal species of the genus. Honey bees exhibited a greater morphological disparity during the Oligocene and, particularly, the Miocene epochs, a time when the principal lineages were established. Contradicting earlier propositions, the geological models allowed a migration via western Europe to north‐western Africa during the Miocene, and the fossil record corroborates such a migration.Main conclusionsFrom the full complement of available data, Apis apparently originated in Europe, spreading from there into Asia, Africa and North America, with subsequent diversification in the former two regions and extinction in the latter. The western honey bee, Apis mellifera, descended from European ancestors that probably migrated from western Europe to Africa during the late Miocene and re‐immigrated into Europe during the Holocene and possibly preceding interglacials.

Geodynamics of the Middle East domain since the Oligocene: research summary

Several analogue models were merged to link the post-Oligocene closure of the Neotethys seaway with the break-up of the Gulf of Aden and the Red Sea. The seaway closure since the early Neogene, which was a result of northwards subduction of Neotethyan lithosphere under south–central Eurasia, generated two styles of kinematic convergence. Its western branch forms the Tethyan subduction under south–central Eurasia along the Hellenic deformation front, generating the break-up of the Aegean Sea and the westward migration of Anatolia. The eastern branch comprises the oblique convergence of Arabia with eastern Anatolia and Iran along the Bitlis–Zagros suture, which gradually shifted from subduction to collision. Because the velocity of plate collision is slower than that of subduction, the subducting section of the underthrust slab moves faster than the colliding segment. Consequently, the underthrust Arabian slab rotated counterclockwise, and developed detachment zones. Such extension triggered the resumption of the propagation of the Carlsberg Ridge into the Gulf of Aden, after being stalled for nearly 30 Ma. It is presumed further that the break-up of the Red Sea in the mid-Miocene was superimposed on the regional uplift and exhumation of the Arabo-Nubian Massif, which was caused by a mantle plume in the Oligocene, a plume that subsequently affected the Ethiopian and the East African plateaux in the Neogene.

Spatial migration of magmatic activity within the Caucasian segment of the Alpine belt in the early neogene under the conditions of geotectonic setting change: Isotope-geochronological data

The Miocene epoch is the most important, possiblykey time range in the Cenozoic history of the Eurasian–Arabian collisional zone (EACZ), in which theNeotethys oceanic basin was finally closed, subduction under the folded structures of the Pontic Mountains and Lesser Caucasis was finished, and the “rigid”stage of convergence between the closed lithosphericplates and microplates and, consequently, uplift andthe formation of grandiose mountain chains and largeplateau of the Caucasus segment within the Alpine–Himalayan folded belt (AHB) started. Change in theregional geotectonic setting resulted in the evolutionof the character of volcanic activity in this part of theEarth from supersubduction magmatism of the continental margin to the typical continental intraplatemagmatism.Without detailed analysis of all (more than 10) published petrological models suggested in recent decadesfor explanation of the reasons for the origin of intraplate magmatism within Eastern Anatolia and theCaucasus, we should note that their totality providestwo basic assumptions.(1) The Late Cenozoic volcanic activity on the territory of the Caucasian segment results from activity ofthe asthenospheric and subasthenospheric mantle.Spreading of the Red Sea plume in the northern direction along the zone of the Levantian transform faultunder the EACZ resulted in the formation of a “hotfield” in the mantle, and the geotectonic setting ofconvergence of continental plates does not play a keyrole in the origin and evolution of young volcanismthere [1, 2, and others].(2) Continental collision is the main reason forintraplate volcanic activity on the territory of the considered region in the Neogene–Quaternary period.Interaction between the large plate and a number ofmicroplates and terranes resulted in steepening, breakoff, and melting of a slab of the oceanic part of theArabian plate (delamination of the lithosphere underthe region, decompression melting in the lower part ofthe crust, etc.), which was previously subducted underthe Pontic Mountains and Lesser Caucasus. In turn,this resulted in passive uplift of the asthenosphericmantle under the Caucasian segment of the AHB andthe origin of magmatism with geochemical characteristics of the intraplate type [3 and others].Undoubtedly, establishment of precise age limitsfor the period of change in the type of magmatic activity in the Caucasus and Eastern Anatolia occurringagainst the background of the gradual evolution of thegeodynamic regime and geotectonic setting in thisregion is one of the fundamental tasks during study ofyoung continental volcanism of the Earth. The previous longterm investigations demonstrated that,according to the geochemical and isotope–geochemical characteristics, Late Miocene magmatism in theGreater Caucasus (8.5–6.0 m. y. ago), Lesser Caucasus (9–5 m. y. ago), and Eastern Anatolia (11–5 m. y.ago) were related to the intraplate type [3–5 and others], whereas the Early Oligocene (35–28 m. y. ago)volcanic activity of the Lesser Caucasian–Pontiac arc(LCPA) was undoubtedly developed in the regime ofthe continental margin above the subduction zone(Fig. 1). In this relation it is necessary to mention thatmarine carbonate rocks of the Burdigal stage are abundant in the central part of Eastern Anatolia. This provides evidence for the existence of the Neotethis deepwater basin there until the middle of the Neogene(16–15 Ma) [7].The period from the end of the Oligocene until thesecond half of the Miocene, thus, covering the transformation of magmatism type in the Caucasus region,was usually considered previously as amagmatic or asa time period with a small scale of volcanic activity[6 and others]. Several years ago we obtained thefirst evidence for the fact that in the Middle Miocene

A goose-sized anseriform bird from the late Oligocene of France: the youngest record and largest species of Romainvilliinae

We describe a new anseriform bird from the late Oligocene of Saint-Andre, Marseille, in southern France. Saintandreachenoides, gen. et sp. nov. is the first avian species reported from the locality, which is well known for its mammalian fossils. The new species belongs to the extinct Romainvilliinae and represents the latest occurrence of the taxon, which was before only known from the late Eocene and early Oligocene of Europe. S.chenoides is also the largest species of Romainvilliinae and increases the known morphological diversity of the taxon. The identification of a goose-sized representative of the Romainvilliinae in the late Oligocene of Europe raises the possibility that some of the large late Paleogene or early Neogene Anseriformes with uncertain phylogenetic affinities also belong to this taxon.

Early Miocene chondrichthyans from the Culebra Formation, Panama: A window into marine vertebrate faunas before closure the Central American Seaway

The newly described chondrichthyan fauna of the early Miocene Culebra Formation of Panama provides insight into the marine vertebrates occupying shallow seas adjacent to the Central American Seaway, prior to the rise of the Isthmus of Panama. This study takes advantage of a time-limited and unique opportunity to recover fossil from renewed excavations of the Panama Canal. The chondrichthyan fauna of the Culebra Formation is composed of teeth and vertebral centra representing 12 taxa. The species found possessed a cosmopolitan tropical and warm-temperate distribution during the early Neogene and are similar to other assemblages of the tropical eastern Pacific and southern Caribbean. The taxa described suggest a neritic environment, and is in contrast with other interpretations that proposed bathyal water depths for the upper member of the Culebra Formation. The wide depth range of the most common species, Carcharocles chubutensis, and the habitat preference of Pristis sp., suggests varied marine environments, from deep, to shallow waters, close to emerged areas of the evolving isthmus.

A multilocus molecular phylogeny of boxfishes (Aracanidae, Ostraciidae; Tetraodontiformes)

Boxfishes (superfamily Ostracioidea, order Tetraodontiformes) are comprised of 37 species within the families Aracanidae (13 sp.) and Ostracidae (24 sp.). These species are characterized by several dramatic reductive trends in their axial and appendicular skeleton, and by the presence of a carapace formed by enlarged and thickened scale plates. While strong support exists for the monophyly of both families, interspecific relationships remain unclear as no species-level molecular phylogeny currently exists for either of these two clades, and the only hypotheses of relationships are based on morphological studies that were mostly restricted to generic-level relationships. Here we present the results of a new phylogenetic study of a dataset composed of 9 loci for 26 species of boxfishes using both likelihood and Bayesian methods. Our topology strongly supports the monophyly of both groups, and additionally provides strongly supported resolution for the vast majority of species-level interrelationships. Based on this new phylogeny, we suggest changing the taxonomic status of the species Lactoria fornasini to Tetrasomus fornasini, and Rhynchostracion nasus to Ostracion nasus. Using a Bayesian approach to divergence time estimation we inferred a Paleocene origin of the Ostracioidea, with an estimated origin of the reef-associated ostraciids spanning the Eocene and Oligocene, and a Miocene/Pliocene origin of the aracanids.

The oldest Odontostomidae (Mollusca: Gastropoda): Bahiensis priscus n. sp. (Paleocene, Uruguay)

The land snail family Odontostomidae has a poor fossil record, mainly from the middle Paleogene and early Neogene of Argentina. In this paper a new species of Odontostomidae from the Paleocene of Uruguay (Queguay Formation) is described. Bahiensis priscus n. sp. represents the first record of the genus Bahiensis Jousseaume 1877, and the oldest record for an Odontostomidae. The new species is characterized by a pupoid fusiform shell and an oval aperture with a single axial columellar fold. Present distribution of the genus indicates a tropical–subtropical environment, in high humidity rate areas.

Late Cretaceous to recent plate motions in western South America revisited

The Andean Cordillera has evolved since the Late Cretaceous in the context of subduction of oceanic lithosphere beneath continental lithosphere, making the kinematics between South America and its adjacent oceanic plates in the Pacific basin valuable to analyze the development of the Andean orogen. The latest Cretaceous–Cenozoic convergence history in western South America may be divided into three stages. The youngest Stage 1 (25–0Ma) is characterized by ENE directed convergence of the Nazca plate toward most of South America, and by ~E–W subduction of the Antarctic plate beneath southern Patagonia. The Nazca–South America convergence rate in Stage 1 shows a continuous decrease from the highest values in the Cenozoic (~15cm/yr) to the present day values from GPS measurements (~7cm/yr). Stage 2 (47–28Ma) is characterized by NE directed subduction of Farallon with the convergence rate remaining almost constant during the entire interval. In those times obliquity was dextral in Chile, sinistral in southern Peru, while almost head-on convergence occurred in central and northern Peru. During latest Cretaceous to Early Eocene times (Stage 3) the Farallon plate was subducted beneath Perú and the Phoenix plate was subducted farther south, where a triple junction migrated southward along the Chilean margin. The subduction of the Farallon plate was rather slow with variable direction imposed by the position of the triple junction, whereas subduction of the Phoenix plate was rapid (>10cm/yr) and ESE directed. We present a working hypothesis suggesting no major changes in the age of subducted lithosphere in the Chile trench from Middle Eocene to Late Oligocene, followed by subduction of progressively older oceanic lithosphere in the early Neogene and progressively younger lithosphere during the late Neogene and the Quaternary. In addition, it is shown that South American motion as predicted by available hotspot models has insufficient resolution to be applied to the analysis of Cenozoic Andean deformation.

Structural control on Meso-Cenozoic tectonic reactivation and denudation in the Siberian Altai: Insights from multi-method thermochronometry

The Siberian Altai forms part of the Central Asian Orogenic Belt and currently is an active intracontinental mountain belt. This Siberian Altai orogen was shaped during multiple phases of intense mountain building and associated denudation throughout the Mesozoic and Cenozoic. We performed a multi-method thermochronometric study on the Altai basement in Siberia in order to distinguish these denudation episodes and to place them in an absolute time-frame. Our data shows that inherited suture zones, such as the Charysh–Terekta–Ulagan–Sayan suture, played a dominant role during this episodic deformation in the Altai. Titanite fission track results reveal Late Triassic–Early Jurassic cooling, which is best expressed in intrusions close to the suture zone. Apatite fission track (AFT) results reveal a second phase of steady basement cooling during the Late Jurassic and Cretaceous. In the suture, AFT and additional apatite (U–Th–Sm)/He (AHe) data reveal a consistent Late Cretaceous–Early Palaeogene phase of fast cooling. We interpret the Mesozoic cooling signals as far-field effects of the Mongol-Okhotsk orogeny. The intense Late Cretaceous–Palaeogene basement cooling signal in the suture zone can be explained as a result of fault-reactivation during the collapse of this orogen and the subsequent re-organization of crustal blocks. During most of the Palaeogene and Early Neogene, basement cooling stagnated, indicating tectonic quiescence. Neogene AHe ages for the Kurai Range, directly adjacent to the suture may reflect renewed rapid cooling as a result of denudation of the present-day Altai mountains. We interpret this most recent cooling as an indirect consequence of stress-propagation from the India–Eurasia collision into the CAOB interior, which thus reached as far as southern Siberia. This study further demonstrates the importance of thermochrological studies on intrusions along major fault-zones in order to date and distinguish fault-reactivation episodes.

Palaeoecology and palaeoenvironment of the Aquitanian locality Ulm-Westtangente (MN2, Lower Freshwater Molasse, Germany)

The mammalian fauna of the German locality Ulm-Westtangente from the Aquitanian Lower Freshwater Molasse is investigated. The fauna is compared to other rich European localities of the same time period. It is shown to be one of the richest localities for fossil mammals and brings interesting insights into the composition of the Aquitanian European faunas. Sixty-one species are identified and high affinities with the French central region are confirmed. Body mass distributions of insectivores, herbivores, omnivores and carnivores are analysed. Altogether, they showed that the environment at Ulm-Westtangente was probably a warm-temperate forest with grassland habitats, although temperature was still difficult to assess. Ulm-Westtangente lies between the Late Oligocene warm-temperate to subtropical conditions prevailing in Europe and the late Early to Middle Miocene very warm subtropical to tropical conditions of the Miocene Climatic Optimum. It thus represents an intermediate stage in the overall climatic evolution of the late Palaeogene–early Neogene of Europe. The comparison of its body mass distribution with a dataset of extant faunas indicates affinities with community structures found in nowadays temperate forests. However, the record of certain types of ectothermic vertebrates at Ulm-Westtangente precludes the presence of a typical temperate climate. The range of carnivore body masses is similar to what is known in extant communities, with species distributed in a restricted size range (small to middle sizes) in comparison to the insectivore/herbivore/omnivore species.

A reappraisal of the brissid echinoid Schizobrissus insignis (Duncan & Sladen) from the middle Eocene of Kachchh, India

The brissid echinoid Schizobrissus insignis (Duncan & Sladen, 1883) is described from the Fulra Limestone (late middle Eocene), in Kachchh, India. Formerly assigned to Peripneustes or to Meoma it is shown that the species possesses a complete subanal fasciole throughout ontogeny, a characteristic feature of Schizobrissus. Eocene species of Schizobrissus and Meoma show several morphological similarities, but diverged during the late Paleogene and early Neogene.

Early Neogene Radiolarian faunal turnover in the northern Indian Ocean: Evidence from Andaman-Nicobar

Two intervals of faunal turnover are revealed by the study of radiolarians from the Early to Middle Miocene sequence of Andaman-Nicobar belonging to Stichocorys wolffii - Calocycletta costata - Dorcadospyris alata zones. These faunal changes are reflected in the values of species diversity, change in abundance of taxa, origination and extinction events and change in radiolarian assemblages. One such faunal change is identified in the latest Early Miocene. The time of this faunal change is marked by the extinction of species like Carpocanopsis cingulata and appearance of Calocycletta costata , Giraffospyris toxaria , Acrocubus octopylus and Liriospyris parkerae , an increasing trend in percentage of cold water species and a decreasing trend in species diversity upwards. The interval coincides with the time of initiation of cooling of sea surface water. Another, and the most prominent faunal turnover of radiolarians is recognized in the Middle Miocene Dorcadospyris alata Zone at about 14.8-12.7 Ma and is characterized by almost complete disappearance of an earlier dominant assemblage and an increase in abundance of an assemblage that was practically absent in the older sequence. The time of this turnover can be correlated with the time of Middle Miocene cooling identified in the examined sequence.

Geothermal regime and hydrocarbon kitchen evolution of the offshore Bohai Bay Basin, North China

The offshore Bohai Bay Basin, located in the central Bohai Bay Basin, north China, one of the most petroliferous basins in China. In this article, based on formation-testing temperature, drill-stem tests, and bottom-hole temperature data, 80 thermal gradient values at the depth interval of 0 to approximately 3000 m (~9843 ft) in the offshore Bohai Bay Basin were obtained. The basinwide average thermal gradient is 31.8 4.6C/km. Based on the above thermal gradient data and the corresponding average weighted thermal conductivity data, 80 measured terrestrial heat flow values were obtained. These values range from 33.5 to 84.0 mW/m2, with an average value of 60.8 8.7 mW/m2. The heat flow and thermal gradient distribution in this region generally show higher values in the uplifts and lower ones in the sags. A thermal history, derived from vitrinite reflectance and apatite fission-track) data, indicates that Paleogene cooling occurred after a period of much higher paleogeothermal gradient (3854C/km). Tectonic subsidence analysis reveals that the area experienced initial synrift subsidence during the Paleogene followed by subsequent thermal subsidence since the Neogene. Thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of petroleum source rock maturation. The maturation and hydrocarbon expulsion histories of the Paleogene Shahejie 3 Formation (E2s3), which is the most important source rock in the offshore Bohai Bay Basin, are modeled. Results show that the Shahejie 3 Formation is in a high mature stage at the present day, and the Bozhong and Qikou sags are the most important kitchens. The Huanghekou sag became the third most important hydrocarbon kitchen in the early Neogene. Based on this hydrocarbon kitchen evolution, oil and gas mainly accumulated after 12 Ma. The evolution of kitchen areas may provide new insights for the understanding of the oil and gas exploration potential of the offshore Bohai Bay Basin.

Geomorphic and cosmogenic nuclide constraints on escarpment evolution in an intraplate setting, Darling Escarpment, Western Australia

AbstractThe ∼900 km long Darling Scarp in Western Australia is one of the most prominent linear topographic features on Earth. Despite the presence of over‐steepened reaches in all westerly flowing streams crossing the scarp, and significant seismic activity within 100 km of the scarp, there is no historical seismicity and no reported evidence for Quaternary tectonic displacements on the underlying Darling Fault. Consequently, it is unclear whether the scarp is a rapidly evolving landform responding to recent tectonic and/or climatic forcing or a more slowly evolving landform. In order to quantify late Quaternary rates of erosion and scarp relief processes, we obtained measurements of the cosmic‐ray produced nuclide beryllium‐10 (10Be) from outcropping bedrock surfaces along the scarp summit and face, in valley floors, and at stream knickpoints. Erosion rates of bedrock outcrops along the scarp summit surface range from 0·5 to 4·0 m Myr−1. These are in the same range as erosion rates of 2·1 to 3·6 m Myr−1 on the scarp face and similar to river incision rates of 2·6 to 11·0 m Myr−1 from valley floor bedrock straths, indicating that the Darling Scarp is a slowly eroding ‘steady state’ landform, without any significant contemporary relief production over the last several 100 kyr and possibly several million years. Knickpoint retreat rates determined from 10Be concentrations at the bases of two knickpoints on small streams incised into the scarp are 36 and 46 m Myr−1. If these erosion rates were sustained over longer timescales, then associated knickpoints may have initiated in the mid‐Tertiary to early Neogene, consistent with early‐mid Tertiary marginal uplift. Ongoing maintenance of stream disequilibrium longitudinal profiles is consistent with slow, regional base level lowering associated with recently proposed continental‐scale tilting, as opposed to differential uplift along discrete faults. Cosmogenic 10Be analysis provides a useful tool for interpreting the palaeoseismic history of intraplate near‐fault landforms over 105 to 106 years. Copyright © 2010 John Wiley & Sons, Ltd.

Miocene ocean circulation inferred from marine carbon cycle modeling combined with benthic isotope records

In a modeling sensitivity study we investigate the evolution of the ocean circulation and of marine carbon isotope (δ13C) records during the Miocene (about 23–5 million years ago). For this purpose we ran an ocean‐circulation carbon cycle model of intermediate complexity (Large Scale Geostrophic– Hamburg Ocean Carbon Cycle Model, version 2s) exploring various seaway configurations. Our investigations confirm that the Central American Seaway played a decisive role in the history of the Miocene ocean circulation. In simulations with a deep Central American Seaway (depth range 1–3 km), typical for the early to middle Miocene, deep water production in the North Atlantic is absent or weak, while the meridional overturning circulation is dominated by water mass formation in the Southern Ocean. Deep water formation in the North Atlantic begins when the Central American Seaway shoals to a few hundreds of meters, which is typical for the late Miocene. Our results do not support ideas that the mid‐Miocene closing of the Eastern Tethys contributed to Antarctic glaciation. On the other hand, we find some water exchange between the Indian Ocean and the Atlantic via the Eastern Tethys during the early Miocene. Our model results for the Atlantic meridional overturning circulation and for Atlantic δ13C during the late Miocene are largely independent from depth variations of the Greenland‐Scotland Ridge. To a large extent, the evolution of Miocene deep‐sea δ13C records can be explained with large‐scale ocean circulation changes. Our model‐data comparison for the middle and early Miocene suggests that during the early Neogene the seaway effect on benthic δ13C may have been superimposed by further factors such as climate regime shifts and/or terrestrial carbon cycle changes.

Oldest cingulate skulls provide congruence between morphological and molecular scenarios of armadillo evolution

The cingulates of the mammalian order Xenarthra present a typical case of disagreement between molecular and morphological phylogenetic studies. We report here the discovery of two new skulls from the Late Oligocene Salla Beds of Bolivia (approx. 26 Ma), which are the oldest known well-preserved cranial remains of the group. A new taxon is described: Kuntinaru boliviensis gen. et sp. nov. A phylogenetic analysis clusters K. boliviensis together with the armadillo subfamily Tolypeutinae. These skulls document an early spotty occurrence for the Tolypeutinae at 26 Ma, in agreement with the temporal predictions of previous molecular studies. The fossil record of tolypeutines is now characterized by a unique occurrence in the Late Oligocene, and a subsequent 12 Myr lack in the fossil record. It is noteworthy that the tolypeutines remain decidedly marginal in the Late Palaeogene and Early Neogene deposits, whereas other cingulate groups diversify. Also, the anatomical phylogenetic analysis herein, which includes K. boliviensis, is congruent with recent molecular phylogenetic analyses. Kuntinaru boliviensis is the oldest confident calibration point available for the whole Cingulata.

The use of MSR (Minimum Sample Richness) for sample assemblage comparisons

Minimum Sample Richness (MSR) is defined as the smallest number of taxa that must be recorded in a sample to achieve a given level of inter-assemblage classification accuracy. MSR is calculated from known or estimated richness and taxonomic similarity. Here we test MSR for strengths and weaknesses by using 167 published mammalian local faunas from the Paleogene and early Neogene of the Quercy and Limagne area (Massif Central, southwestern France), and then apply MSR to 84 Oligo-Miocene faunas from Riversleigh, northwestern Queensland, Australia. In many cases, MSR is able to detect the assemblages in the data set that are potentially too incomplete to be used in a similarity-based comparative taxonomic analysis. The results show that the use of MSR significantly improves the quality of the clustering of fossil assemblages. We conclude that this method can screen sample assemblages that are not representative of their underlying original living communities. Ultimately, it can be used to identify which assemblages require further sampling before being included in a comparative analysis.

Tectonic and sedimentary evolution of the frontal part of an ancient subduction complex at the transition from accretion to erosion: The case of the Ligurian wedge of the northern Apennines, Italy

Subduction can be associated either with accretion or with removal of material from the overriding plate. These two processes can either coexist or alternate in time along the same margin. Their inception has the potential to change the dynamic equilibrium of a marginal wedge resulting in the development of out-of-sequence thrusts, normal and strike-slip faults, or large submarine landslides in the frontal part of the subduction zone. In this work we investigate the effects of the transition from frontal accretion to frontal erosion on the stability of a subduction complex through the study of an ancient example from the northern Apennines (Ligurian subduction complex). New structural data suggest that in the early Neogene (Aquitanian), the removal and underthrusting of the toe of the wedge, formed by both the accreted oceanic sediments and the overlying wedge-top basin fill (i.e., the Subligurian units), implied a process of frontal tectonic erosion. The presence, on top of the subduction complex, of a complete succession of mid-late Eocene to late Miocene slope-apron sediments—i.e., the Epiligurian succession—facilitates a reconstruction of the sedimentary response to this event. In the Aquitanian, large areas of the wedge were denuded from the lower-slope sedimentary cover through extensive gravitational mass movements. The subsequent deposition of a thick body of submarine debris flows is documented. The mass-wasting deposits are interpreted as the sedimentary response to the underthrusting of the frontal part of the Ligurian subduction complex formed by the Subligurian units.