Late Early Pliocene Research Articles

The late Neogene Sahabi rivers of the Sahara and the hamadas of the eastern Libya–Chad border area

This paper contributes to the concept that during the late Tortonian, Messinian and early Pliocene ( c. 7.5–4.6 Ma) in addition to the Nile the Sahabi rivers also crossed the Sahara, having originated from tropical Neogene Lake Chad. Examination of two hamadas lying just to the north of the Libya–Chad border using Landsat images and SRTM topographic data enables one of them, Hamada Ibn Battutah West, to be recognised as an uplifted palaeosurface which preserves late Miocene/early Pliocene fluvial activity. This surface is referred to as the Yangara Palaeosurface. Of particular interest on the hamada are two long ( c. 50 km), wide ( c. 4 km) channels, a 50 km 2 relic landscape and a short well defined 5 km channel about 1 km wide. The location of Hamada Ibn Battutah West is significant because the hamada provides evidence of extensive fluvial activity part way between the place of origin of the Sahabi rivers and their preserved record at the Gulf of Sirt. The Yangara Palaeosurface is considered to extend southwards to the adjacent hamada in northeastern Chad. The total palaeosurface extends 165 km in an approximate north–south direction and averages 45 km in width. It lies in the central part of an area of complex post-Miocene uplift involving four hamadas at the Libya–Chad border.

Systematic and biostratigraphic significance of a chinchillid rodent from the Pliocene of eastern Argentina

Fil: Rasia, Luciano Luis. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Division Paleontologia Vertebrados; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

The Neogene transition from C3to C4grasslands in North America: assemblage analysis of fossil phytoliths

The rapid ecological expansion of grasses with C4photosynthesis at the end of the Neogene (8–2 Ma) is well documented in the fossil record of stable carbon isotopes. As one of the most profound vegetation changes to occur in recent geologic time, it paved the way for modern tropical grassland ecosystems. Changes in CO2levels, seasonality, aridity, herbivory, and fire regime have all been suggested as potential triggers for this broadly synchronous change, long after the evolutionary origin of the C4pathway in grasses. To date, these hypotheses have suffered from a lack of direct evidence for floral composition and structure during this important transition. This study aimed to remedy the problem by providing the first direct, relatively continuous record of vegetation change for the Great Plains of North America for the critical interval (ca. 12–2 Ma) using plant silica (phytolith) assemblages.Phytoliths were extracted from late Miocene-Pliocene paleosols in Nebraska and Kansas. Quantitative phytolith analysis of the 14 best-preserved assemblages indicates that habitats varied substantially in openness during the middle to late Miocene but became more uniformly open, corresponding to relatively open grassland or savanna, during the late Miocene and early Pliocene. Phytolith data also point to a marked increase of grass short cells typical of chloridoid and other potentially C4grasses of the PACMAD clade between 8 and 5 Ma; these data suggest that the proportion of these grasses reached up to ∼50–60% of grasses, resulting in mixed C3-C4and highly heterogeneous grassland communities by 5.5 Ma. This scenario is consistent with interpretations of isotopic records from paleosol carbonates and ungulate tooth enamel. The rise in abundance of chloridoids, which were present in the central Great Plains since the early Miocene, demonstrates that the “globally” observed lag between C4grass evolution/taxonomic diversification and ecological expansion occurred at the regional scale. These patterns of vegetation alteration imply that environmental change during the late Miocene-Pliocene played a major role in the C3-C4shift in the Great Plains. Specifically, the importance of chloridoids as well as a decline in the relative abundance of forest indicator taxa, including palms, point to climatic drying as a key trigger for C4dominance.

Evolutionary origins and diversification of dragon lizards in Australia’s tropical savannas

Australia’s monsoonal tropics are dominated by the largest and least modified savanna woodlands in the world, and they are globally significant for their high biodiversity and regional endemism. Despite this, there have been very few molecular studies of the evolutionary origins and diversification of vertebrates in this region. The semi-arboreal dragon lizards of Lophognathus and Amphibolurus are widely distributed in the savanna and dry sclerophyll woodlands of Australasia, including the monsoon tropics. We sequenced a ∼1400bp region of mitochondrial DNA and a ∼1400bp nuclear gene (RAG1) to investigate the phylogenetic relationships and phylogeographic structuring of all seven species of Lophognathus and Amphibolurus. Our analyses show that there is a higher level of species and generic diversity in the monsoon tropics than previously thought, and a full morphological review and taxonomic revision of these genera is required. Relaxed molecular clock analyses indicate that species across both genera originated in the late Miocene and early Pliocene, with significant phylogeographic structure within species. We did not find any evidence that the monsoon tropics species were a monophyletic group that had diversified within the region; instead Amphibolurus and Lophognathus represent at least three independent evolutionary colonizations of the monsoon tropics. It is probable that the origins and phylogeographic patterns of the northern Lophognathus species have evolved under the climatic influence of the Australian monsoon, rather than being either an ancient Gondwanan lineage that pre-dates the monsoon or the result of a more recent dispersal event across Wallace’s Line.

Zullobalanus santamariaensis sp. nov., a new late Miocene barnacle species of the family Archaeobalanidae (Cirripedia: Thoracica), from the Azores

A new species of Archaeobalanidae barnacle is described from the late Miocene and early Pliocene of Santa Maria Island (Azores). Samples were collected primarily from outcrops at Malbusca and “Pedra-que-Pica”. Zullobalanus santamariaensis sp. nov. is endemic to the Azores archipelago and until the discovery of this material, the genus was known only from the Southern Hemisphere. For such a long-range distribution we assume a combination of planktotrophic larval development, sea-surface oceanic currents and transport by cetaceans. This study endorses the elevation of the subgenus Zullobalanus to generic level.

First Alaocybites weevil (Insecta: Coleoptera: Curculionoidea) from the Eastern Palaearctic: a new microphthalmic species and generic relationships

The genus Alaocybites (Coleoptera: Curculionoidea), previously consisting of two eyeless Californian species, is for the fi rst time reported from the East Palaearctic Region. A new microphthalmic species, A. egorovi sp.n., is described from Primor-sky Kray, the Far East of Russia. An early Late Pliocene Alaskan weevil fossil previously attributed to the molytine genus Otibazo is assigned to Alaocybites and found almost undistinguishable from A. egorovi sp.n. Results of preliminary phylo-genetic analyses aimed to clarify phylogenetic affinities of Alaocybites are found controversial and inconclusive. The uncer-tainties of the contemporary classifi cation of orthocerous weevils are briefl y discussed. Alaocybites is provisionally retained in Raymondionymidae, with the absence of tarsomere IV on each leg being the family's most plausible apomorphy. Mono-phyly, geographical distribution and internal relationships of Raymondionymidae are briefl y discussed and compared with other predominantly Mediterranean groups of eyeless beetles. External and genital morphological characters of edaphic weevils with reduced eyes habitually resembling, or thought to be related to, Alaocybites are extensively illustrated.

A magnetostratigraphic record of landscape development in the eastern Ordos Plateau, China: Transition from Late Miocene and Early Pliocene stacked sedimentation to Late Pliocene and Quaternary uplift and incision by the Yellow River

A continuous fluviolacustrine record provides the geochronological framework to reconstruct the fluvial landscape evolution of the middle reach of the Huanghe (Yellow River). Magnetostratigraphic records from six sections at the north of the Jinshaan Gorge indicate that an isolated fluviolacustrine system occupied this gorge from 8.3 to 3.7 Ma. Local fluvial incision initiated at the lake margin around 5.3-4.9 Ma, and concomitant fluvial deposits intruded laterally into fine lacustrine strata increasing the sedimentation rate (ca. 3.1 cm/ky) within the isolated lake. The temporal coincidence of the onset of uplift-driven valley incision at 3.7 Ma along the Yellow River and the onset of basin excavation suggest that uplift possibly played an important role in the late Pliocene-Quaternary drainage evolution. Consequently, incision of the Yellow River upstream in the Jinshaan Gorge initiated at 3.7 Ma.

Tectono-sedimentary events and geodynamic evolution of the Mesozoic and Cenozoic basins of the Alpine Margin, Gulf of Tunis, north-eastern Tunisia offshore

The structural pattern, tectono-sedimentary framework and geodynamic evolution for Mesozoic and Cenozoic deep structures of the Gulf of Tunis (north-eastern Tunisia) are proposed using petroleum well data and a 2-D seismic interpretation. The structural system of the study area is marked by two sets of faults that control the Mesozoic subsidence and inversions during the Paleogene and Neogene times: (i) a NE-SW striking set associated with folds and faults, which have a reverse component; and (ii) a NW–SE striking set active during the Tertiary extension episodes and delineating grabens and subsiding synclines. In order to better characterize the tectono-sedimentary evolution of the Gulf of Tunis structures, seismic data interpretations are compared to stratigraphic and structural data from wells and neighbouring outcrops. The Atlas and external Tell belonged to the southernmost Tethyan margin record a geodynamic evolution including: (i) rifting periods of subsidence and Tethyan oceanic accretions from Triassic until Early Cretaceous: we recognized high subsiding zones (Raja and Carthage domains), less subsiding zones (Gamart domain) and a completely emerged area (Raouad domain); (ii) compressive events during the Cenozoic with relaxation periods of the Oligocene-Aquitanian and Messinian-Early Pliocene. The NW–SE Late Eocene and Tortonian compressive events caused local inversions with sealed and eroded folded structures. During Middle to Late Miocene and Early Pliocene, we have identified depocentre structures corresponding to half-grabens and synclines in the Carthage and Karkouane domains. The north–south contractional events at the end of Early Pliocene and Late Pliocene periods are associated with significant inversion of subsidence and synsedimentary folded structures. Structuring and major tectonic events, recognized in the Gulf of Tunis, are linked to the common geodynamic evolution of the north African and western Mediterranean basins.

Structural analysis of the coseismic shear zone of the 2008 M w 7.9 Wenchuan earthquake, China

Field investigations reveal that the surface rupture of the 2008 M w 7.9 Wenchuan earthquake, China, occurred along a pre-existing shear zone in the Longmen Shan Thrust Belt. Structural analyses of the coseismic fault zone and fault rocks show that i) the main coseismic shear zone consists of a fault core that includes a narrow fault gouge zone of <15 cm in width (generally 1–2 cm) and a fault breccia zone of <∼3 m in width, and a wide damage zone of >5 m in width that is composed of cataclastic rocks including fractures and subsidiary faults; ii) the foliations developed in the fault core and damage zones indicate a dominantly thrust slip sense, consistent with that indicated by the coseismic surface rupture; and iii) coseismic slip was largely localized to within a narrow fault gouge zone of <2–3 mm in width. The structural characteristics of the coseismic shear zone and cataclastic rocks indicate that the location of coseismic slip zone associated with the 2008 Wenchuan earthquake was controlled by a pre-existing shear zone and that the main active fault of the Longmen Shan Thrust Belt has moved as a thrust since the formation of cataclastic rocks along the fault during the late Miocene or early Pliocene.

Plio-Pleistocene paleoclimate in the Southwest Pacific as reflected in clay mineralogy and particle size at ODP Site 1119, SE New Zealand

Clay mineralogical and particle size data from Ocean Drilling Program (ODP) Site 1119 reflect processes associated with the deposition of the Canterbury Drifts and the evolution of the New Zealand south-eastern shelf, and are strongly correlated with Pliocene–Pleistocene climatic and oceanographic fluctuations. Elevated smectite contents at the base of Site 1119 (latest Early Pliocene ∼ 3.9–3.5 Ma) also occur regionally in the Southern Ocean and point towards an alternative sediment source other than nearby New Zealand terranes. The abrupt reduction in smectite content at ∼ 3.5 Ma and replacement by dominant chlorite–illite assemblages corresponds to the onset of Late Pliocene cooling climate conditions and more intense onland physical weathering. High illite contents in Late Pliocene–Early Pleistocene (∼ 3.0–1.7 Ma) sediments suggest a more southern terrane (e.g. Haast Schist) source influence and widened shelf conditions. An upward increase in clay content reflects an increased supply of glacier-derived detrital sediment, concurrent with global climate deterioration during the Late Pliocene–Pleistocene. Grainsize fining of the background mean sortable silt (mss) signal indicates reduced Southland Current flow, consistent with its forced seaward migration across Site 1119 over time due to continual eastward shelf progradation. Clay mineralogy and particle size data at ODP Site 1119 exhibit a relationship with both global climatic conditions and with Southwest Pacific paleoceanographic and paleoclimatic regimes.

Biogeography of Cedrela (Meliaceae, Sapindales) in Central and South America

Dated phylogenies have helped clarify the complex history of many plant families that today are restricted to the world's tropical forests, but that have Eocene, Oligocene, and Miocene fossils from the northern hemisphere. One such family is the Meliaceae. Here we infer the history of the neotropical Meliaceae genus Cedrela (17 species), the sister clade of which today is restricted to tropical Asia. Sequences from the nuclear ribosomal spacer region and five plastid loci obtained for all ingroup species and relevant outgroups were used to infer species relationships and for molecular-clock dating under two Bayesian relaxed clock models. The clock models differed in their handling of rate autocorrelation and sets of fossil constraints. Results suggest that (1) crown group diversification in Cedrela started in the Oligocene/Early Miocene and intensified in the Late Miocene and Early Pliocene, and (2) Central American Cedrela species do not form a clade, implying reentry into Central America after the closure of the Panamanian Isthmus. At present, Cedrela is distributed in both dry and humid habitats, but morphological features suggest an origin in dry forest under seasonal climates, fitting with Miocene and Pliocene Cedrela fossils from deciduous forests.

Diatomaceous sedimentation in late Neogene lacustrine basins of western Macedonia, Greece

Several lacustrine basins were formed by late Miocene tectonic processes in western Macedonia, Greece. These were occupied by a series of lakes and wetland swamps during the late Miocene and early Pliocene giving rise to diatomaceous claystones, siltstones and diatom-bearing tufa deposits. Diatoms are rare or fragmentary in sandstones and chemical sediments, and are absent in conglomerates. The Fe2+-rich phosphate minerals anapaite and vivianite are present in parts of the diatomaceous siltstones. Six major diatom groups were identified using cluster and correspondence analyses, each of which tends to be associated with a particular lithofacies. The floras are indicative of mildly acidic to alkaline water of varying depths. The dominant taxa include Aulacoseira ambigua, A. distans, Cyclotella iris and several of its varieties, C. aegeae, C. castracanei, C. elymaea, C. ocellata, and two unidentified Cyclotella. Fragilariaceae are common, consisting mainly of Fragilaria bituminosa, Pseudostaurosira brevistriata, P. zeilleri, Staurosira construens, Staurosirella leptostauron, and S. pinnata. Locally, chysophycean stomatocysts are common, suggesting more oligotrophic conditions. Nine diatom stages are recognized in the Lower Neogene Series at Kariditsa (Kozani basin), reflecting shallow swamps, small alkaline lakes, and terrestrial settings. The Upper Neogene Series rocks are characterized by Mg-rich carbonates such as hydromagnesite, huntite and magnesite. A detailed stratigraphy was developed for Mio-Pliocene deposits in the Florina basin at Klidi. Parts of this sequence show clear cyclicity in both the sediments and the diatom floras, with shallow-water diatoms repeatedly giving way to taxa indicative of deeper conditions. Larger-scale, shallow-deep cycles are also present and may be related to precession- and eccentricity-forced climate change.

Evidence for iceberg armadas from East Antarctica in the Southern Ocean during the late Miocene and early Pliocene

Abstract Sediments from Ocean Drilling Program Site 1165 in the Indian Ocean sector of the Southern Ocean (off Prydz Bay) contain a series of layers that are rich in ice-rafted debris (IRD). Here we present evidence that IRD-rich layers at Site 1165 at 7, 4.8, and 3.5 Ma record short-lived, massive discharges of icebergs from Wilkes Land and Adelie Land, more than 1500 kilometers to the east of the depositional site. This distant source of icebergs is clearly defined by the presence of IRD hornblende grains with 40Ar/39Ar ages of 1200–1100 Ma and 1550–1500 Ma, ages that are not found on the East Antarctic continent in locations closer to Site 1165. This observation requires enormous amounts of detritus-carrying drifting icebergs, most likely in the form of large icebergs. These events probably reflect destabilization, surge, and break-up of ice streams on the Wilkes Land and Adelie Land margins of the East Antarctic Ice Sheet, in the vicinity of the low-lying Aurora and Wilkes Basins. They occurred under warming conditions, but each coast seems to have produced ice-rafting events independently, at different times. The data presented here constitute the first evidence of far-traveled icebergs from specific source areas around the East Antarctic perimeter. Launch of these icebergs may have happened during quite dramatic events, perhaps analogous to “Heinrich Events” in the North Atlantic.

Timing, controls and consequences of compression in the Rockall-Faroe area of the NE Atlantic Margin

Abstract The simplest models of passive margins would suggest that they are characterized by tectonic quiescence as they experienced gentle thermal subsidence following the extensional events that originally formed them. Analysis of newly acquired and pre-existing 2D seismic data from the Rockall Plateau to the Faroe Shelf, however, has confirmed that the NE Atlantic Margin was the site of significant active deformation. Seismic data have revealed the presence of numerous compression-related Cenozoic folds, such as the Hatton Bank, Alpin, Ymir Ridge and Wyville–Thomson Ridge Anticlines. The distribution, timing of formation and nature of these structures have provided new insights into the controls and effects of contractional deformation in the region. Growth of these compressional features occurred in five main phases: Thanetian, late Ypresian, late Lutetian, Late Eocene (C30) and Early Oligocene. Compression has been linked to hotspot-influenced ridge push, far-field Alpine and Pyrenean compression, asthenospheric upwelling and associated depth-dependent stretching. Regional studies make it clear that compression can have a profound effect on seabed bathymetry and consequent bottom-water current activity. Bottom-water currents have directly formed the early Late Oligocene, late Early Miocene (C20), Late Miocene–Early Pliocene, and late Early Pliocene (C10) unconformities. The present-day Norwegian Sea Overflow (NSO) from the Faroe–Shetland Channel into the Rockall Trough is restricted by the Wyville–Ymir Ridge Complex, and takes place via the syncline (Auðhumla Basin) between the two ridges. The Auðhumla Basin Syncline is now thought to have controlled the path of the NSO into the Rockall Trough and the resulting unconformity formation and sedimentation therein, no later than the Mid Miocene.

Low-latitude northern hemisphere oceanographic andclimatic responses to early shoaling of the Central American Seaway

The opening and closing of ocean gateways has played a major role in shaping global climate by altering oceanic and atmospheric circulation. This study uses planktonic foraminifer assemblage-based sea surface temperature (SST) estimates (Modern Analog Technique) to examine the eastern tropical Pacific (ETP) and subtropical Northwest Atlantic (NWA) during the early stages of shoaling of the Central American Seaway (CAS). In the subtropical NWA (DSDP 103 and ODP 1006), the 5.2 to 5.1 Ma interval is characterized by an increase in SST and sea surface salinity, indicating a strengthening of the Florida Current (FC) and Gulf Stream (GS). Sea surface temperature in the ETP Warm Pool (DSDP Site 84) remained relatively stable between 6.9 and 5.1 Ma, during which El Niño-like conditions persisted. A slight cooling is observed after this interval (with synchronous warming in the NWA), followed by the onset of major cooling at ∼3.2 Ma, both of which are preceded by a shallowing of the thermocline. Stepwise cooling is attributed to enhanced Atlantic meridional overturn cicrulation (AMOC), which caused a shoaling of the main tropical thermocline, thereby strengthening the Walker Circulation and weakening the Pacific North Equatorial Counter Current. Antithetical changes in surface current strength in the NWA and ETP suggest a southward migration of the Intertropical Convergence Zone ∼4.3 Ma. During the mid-Pliocene, SST in the Panama Basin was ∼0.8°C cooler than today, while the subtropical NWA was only ∼1.1°C warmer. This corroborates evidence for reduced meridional SST gradients during the mid-Pliocene as well as the hypothesis that more vigorous ocean circulation-particularly in the NWA-was critical during this period. The timing of SST changes in the ETP and NWA (∼5.1 Ma) suggest that the termination of permanent El Niño and enhanced AMOC did not contribute significantly to the onset of major Northern Hemisphere glaciation (NHG), as both of these events occur well before the beginning of the glacial cycles. However, these processes may have contributed to the development of the small ice sheets of the late Miocene and early Pliocene, but were most likely only preconditioning factors for the onset of major NHG. However, changes in SST and relative thermocline position suggest that high-latitude processes and global cooling may have influenced thermal structure in the ETP. The SST estimates provided indicate that even in its early stages, the shoaling of the CAS had significant implications for low-latitude ocean circulation and thermal structure, as well as for some of the most significant global climate events of the late Neogene.

Neogene Decapod Crustacea from Southern Chile

ABSTRACT Twelve species of Neogene decapod crustaceans are described from late Miocene and early Pliocene deposits in the Valdivia, Osomo-Llanquihue, and Chiloe basins as well as from Mocha Island, offshore from the Temuco Basin, southern Chile. New species of thalassinideans include Ctenocheles notialis and Axianassa? chilensis. Axianassa Schmitt, 1924, has not been reported previously in the fossil record. New species of brachyurans include Trichopeltarion frassinetti. Pirulella antipodea, Chaceon quadrata, Geryon manningi, Phenophthalmus mochaensis, and Chasmocarcinus chiloeensis. Pirulella and Phenophthalmus are new genera and Geryon Kroyer, 1837, is noted in the fossil record for the first time. Extant congeners are primarily known from lower latitude regions. Only Chaceon Manning and Holthuis, 1989, is known from the Chilean coast at present.

Palynostratigraphy and vegetation characteristics of Neogene continental deposits interbedded with the Cappadocia ignimbrites (Central Anatolia, Turkey)

A palynological analysis of the Late Miocene and Early Pliocene successions of the Cappadocian Volcanic Province (Central Anatolia, Turkey) has been carried out with the aim of reconstructing the palaeovegetation and palaeoclimatic conditions. The samples are collected from outcrop sections from three different localities (A: Akdag, B: Bayramhacili and G: Guzeloz). The pollen spectra reveals the existence of a steppe vegetation dominated by Amaranthaceae–Chenopodiaceae and Artemisia, typical of present day arid and semi-arid continental areas (i.e. Middle East), and Asteraceae Asteroideae in the A section (Late Miocene) developed in arid climatic conditions. The flora of the G (Early Pliocene) and lower part of the B (Late Miocene) sections reflects steppes on which Asteraceae Asteroideae was dominant. This flora also indicates arid conditions. The development of trees in the upper part of the B section was possibly related to local paleoenvironmental conditions rather than a climatic change. This study provides the first palynological data to reveal the presence of an Amaranthaceae–Chenopodiaceae and Artemisia steppe already during the Late Miocene in Turkey.

Siliciclastic influx and burial of the Cenozoic carbonate system in the Gulf of Papua

An extensive carbonate system in the Gulf of Papua (GoP), developed in the late Oligocene–middle Miocene, was buried by huge influx of siliciclastics originated from Papua New Guinea. Major episodes of siliciclastic influx in the carbonate system are related to tectonic activity in the fold and thrust belt during the Oligocene Peninsular Orogeny, late Miocene Central Range Orogeny, and late Pliocene renewed uplift and exhumation of peninsular region. Siliciclastics did not influence the carbonate deposition during the late Oligocene–middle Miocene, since they were accumulated in the Aure Trough, proximal foreland basin protecting the carbonate system. The most significant burial of the carbonate system started during the late Miocene–early Pliocene in the result of the Central Range Orogeny. However, the largest influx was related to the renewed uplift of the Papuan Peninsula during the early late Pliocene. The shelf edge prograded ∼150 km and formed more than 80% of the modern shelf. This high siliciclastic influx was also enhanced by the “mid” Pliocene global warmth period and intensified East Asian monsoons at 3.6–2.9 Ma. Although many publications exist on carbonate–siliciclastic mixing in different depositional environments, this study helps understand the carbonate–siliciclastic interactions in space and time, especially at basinal scale, and during different intervals of the carbonate system burial by siliciclastic sediments.

Phylogenetic Systematics of the North American Fossil Caninae (Carnivora: Canidae)

The canid subfamily Caninae includes all the living canids and their most recent fossil relatives. Their sister taxon is the Borophaginae with which they share an important modification of the lower carnassial, namely the presence of a bicuspid talonid, which gives this tooth an additional function in mastication. Contributing to this function is the enlargement of the posterolingual cingulum of M1 and development of a hypocone. The Caninae diverged from the Borophaginae in the narrowing and elongation of the premolars separated by diastemata and placed in a shallow ramus and narrow muzzle. These latter features allow the Caninae to be recognized in the fossil record as early as the beginning of the Oligocene (34 Ma) and constitute evidence that they represent a monophyletic group.In striking contrast to the history of the Borophaginae, the Caninae remain confined to a closely similar group of fox-sized species (Leptocyon spp.) throughout the Oligocene and showing very limited cladogenesis into the end of the medial Miocene (12 Ma), a span that saw marked adaptive divergence in the Borophaginae and the origin of all its major clades. By 12 Ma (beginning of the Clarendonian Land Mammal age) few fox-sized borophagines remained and most of those held hypocarnivorus adaptations. At that point the Vulpini appear both as mesocarnivores (Vulpes spp.) and hypocarnivores (Metalopex spp.) reproducing, on a much smaller scale, the range of adaptations shown in the initial radiation of the Borophaginae.By the end of the Clarendonian (9 Ma) the first members of the tribe Canini appear. Initially this group was represented by the genus Eucyon, largely by a single widespread North American species E. davisi. Our cladistic analysis predicts that the roots of the South American clade subtribe Cerdocyonina, sister taxon to E. davisi and Canis species (together, subtribe Canina), must also have been present, but taxa representing this group do not appear in the North America record until the earliest Pliocene (latest Hemphillian, 5 Ma). Species of three genera (Cerdocyon, Chrysocyon, and possibly Theriodictis), now confined to South America, appear in the fossil record of the southern United States and northern Mexico prior to and just after the opening of the Panamanian Isthmus (ca. 3 Ma), indicating that important cladogenesis within the South American clade took place in North America. Species of Eucyon make their appearance in the Old World in the late Miocene, and E. davisi has a Pliocene record in Asia. Species of this genus undergo a modest adaptive radiation in Eurasia during the Pliocene.In the late Miocene and early Pliocene two species of Canis appear in North America (C. ferox and C. lepophagus), representing the initial cladogenesis within the genus. These animals are all coyote-sized and represent a broadening of body size range within a mesocarnivorous dental adaptation. Toward the end of the Pliocene and into the Pleistocene in North America a curious and rare group of jackal-like species (C. thöoides, C. feneus, and C. cedazoensis) seem to form an endemic clade arising near C. lepophagus. These taxa are dentally similar to jackals, especially C. aureus, but share no synapomorphies with them.The early cladogenesis of Canis in the Pliocene of North America produced a somewhat larger form, C. edwardii, that appears in the late Blancan at ca. 3 Ma. It also seems to have a sister relationship with C. lepophagus and with the coyote C. latrans, which appears much later in the record (late Irvingtonian) and quickly becomes distributed across the United States. The golden jackal (C. aureus) shares synapomorphies with the coyote and C. edwardii but does not appear in the fossil record until the early Pleistocene of North Africa. Canis edwardii is extinct by the end of the Irvingtonian.Large wolflike species of Canis seem to be the products of evolution in Eurasia. They appear early in the North American record as immigrants of the crown g

Increasing long-wavelength relief across the southeastern flank of the Sierra Nevada, California

A high degree of correlation between present-day relative rock uplift measured using continuous GPS geodesy and spatially averaged surface elevations suggests that long-wavelength topographic relief is presently increasing along the southeastern flank of the Sierra Nevada range and within an adjacent portion of the northern Basin and Range province. Current estimates for erosion rate are an order of magnitude smaller than the relative rates determined by geodesy. Thus, although the uplift serves to enhance long-wavelength relief, it cannot be explained entirely as an isostatic response to erosion. If uplift rates have been constant through time, the duration over which the uplift could have been active (<1.6 Myrs) is shorter than expected based on our current understanding of the geodynamic history of the region. One possible explanation for the observed present-day uplift pattern is that it represents an ongoing isostatic response to gradual reduction of the equivalent elastic thickness (EET) of the lithosphere under temporally constant loads. Another explanation is that the loads currently supporting the high elevations of the southern Sierra are evolving with time. According to either hypothesis, vertical surface motions may have slowly accelerated since ~mid-Pliocene time. Several possible mechanisms for progressive reduction of EET may be attributable to thermo-mechanical disequilibrium that began with the removal of an ultramafic root from the Sierran batholith during late Miocene or early Pliocene time. Specific mechanisms for ongoing enhancement of loads are less obvious. Based on these results, we suggest that dense networks of long-running continuous GPS stations around the world currently represent an underutilized resource for studies of orogenesis and upper mantle processes.