Home About us Contact
|
Home About us Contact | ||
|
|
||
Early Miocene (early + miocene)
Selected AbstractsOrigin and geochemistry of Miocene marine evaporites associated with red beds: Great Kavir Basin, Central IranGEOLOGICAL JOURNAL, Issue 1 2007Hossain Rahimpour-Bonab Abstract During the Cenozoic numerous shallow epicontinental evaporite basins formed due to tectonic movements in the Northern Province of the Central Iran Tectonic Zone (the Great Kavir Basin). During the Miocene, due to sea-level fluctuations, thick sequences of evaporites and carbonates accumulated in these basins that subsequently were overlain by continental red beds. Development of halite evaporites with substantial thickness in this area implies inflow of seawater along the narrow continental rift axis. The early ocean basin development was initiated in Early Eocene time and continued up to the Middle Miocene in the isolated failed rift arms. Competition between marine and non-marine environments, at the edge of the encroaching sea, produced several sequences of both abrupt and gradual transition from continental wadi sediments to marginal marine evaporites in the studied area. These evaporites show well-preserved textures indicative of relatively shallow-brine pools. The high Br content of these evaporites indicates marine-derived parent brines that were under the sporadic influence of freshening by meteoric water or replenishing seawater. However, the association of hopper and cornet textures denotes stratified brine that filled a relatively large pool and prevented rapid variations in the Br profile. Unstable basin conditions that triggered modification of parent brine chemistry prevailed in this basin and caused variable distribution patterns for different elements in the chloride units. The presence of sylvite and the absence of Mg-sulphate/chlorides in the paragenetic sequence indicate SO4,depleted parent brine in the studied sequence. Petrographic examinations along with geochemical analyses on these potash-bearing halites reveal parental brines which were a mixture of seawater and CaCl2 -rich brines. The source of CaCl2 -rich brines is ascribed to the presence of local rift systems in the Great Kavir Basin up to the end of the Early Miocene. Copyright © 2007 John Wiley & Sons, Ltd. [source] Evidence for two episodes of volcanism in the Bigadiç borate basin and tectonic implications for western TurkeyGEOLOGICAL JOURNAL, Issue 5 2005Fuat Erkül Abstract Western Turkey has been dominated by N,S extension since the Early Miocene. The timing and cause of this N,S extension and related basin formation have been the subject of much debate, but new data from the Bigadiç borate basin provide insights that may solve this controversy. The basin is located in the Bornova Flysch Zone, which is thought to have formed as a major NE-trending transform zone during Late Cretaceous-Palaeocene collisional Tethyan orogenesis and later reactivated as a transfer zone of weakness, and which separates two orogenic domains having different structural evolutions. Volcanism in the Bigadiç area is characterized by two rock units that are separated by an angular unconformity. These are: (1) the Kocaiskan volcanites that gives K/Ar ages of 23,Ma, and (2) the Bigadiç volcano-sedimentary succession that yields ages of 20.6 to 17.8,Ma. Both units are unconformably overlain by Upper Miocene-Pliocene continental deposits. The Kocaiskan volcanites are related to the first episode of volcanic activity and comprise thick volcanogenic sedimentary rocks derived from subaerial andesitic intrusions, domes, lava flows and pyroclastic rocks. The second episode of volcanic activity, represented by basaltic to rhyolitic lavas and pyroclastic rocks, accompanied lacustrine,evaporitic sedimentation. Dacitic to rhyolitic volcanic rocks, called the S,nd,rg, volcanites, comprise NE-trending intrusions producing lava flows, ignimbrites, ash-fall deposits and associated volcanogenic sedimentary rocks. Other NE-trending olivine basaltic (Gölcük basalt) and trachyandesitic (Kay,rlar volcanites) intrusions and lava flows were synchronously emplaced into the lacustrine sediments. The intrusions typically display peperitic rocks along their contacts with the sedimentary rocks. It is important to note that the Gölcük basalt described here is the first recorded Early Miocene alkali basalt in western Turkey. The oldest volcanic episode occurred in the NE-trending zone when the region was still experiencing N,S compression. The angular unconformity between the two volcanic episodes marks an abrupt transition from N,S collision-related convergence to N,S extension related to retreat of the Aegean subduction zone to the south along an extensional detachment. Thrust faults with top-to-the-north sense of shear and a series of anticlines and synclines with subvertical NE-striking axial planes observed in the Bigadiç volcano-sedimentary succession suggest that NW,SE compression was reactivated following sedimentation. Geochemical data from the Bigadiç area also support the validity of the extensional regime, which was characterized by a bimodal volcanism related to extrusion of coeval alkaline and calc-alkaline volcanic rocks during the second volcanic episode. The formation of alkaline volcanic rocks dated as 19.7,±,0.4,Ma can be related directly to the onset of the N,S extensional regime in western Turkey. Copyright © 2005 John Wiley & Sons, Ltd. [source] Small mammal (rodents and lagomorphs) European biogeography from the Late Oligocene to the mid PlioceneGLOBAL ECOLOGY, Issue 4 2007Olivier Maridet ABSTRACT Aim, To analyse the fossil species assemblages of rodents and lagomorphs from the European Neogene in order to assess what factors control small mammal biogeography at a deep-time evolutionary time-scale. Location, Western Europe: 626 fossil-bearing localities located within 31 regions and distributed among 18 successive biochronological units ranging from c. 27 Ma (million years ago; Late Oligocene) to c. 3 Ma (mid Pliocene). Methods, Taxonomically homogenized pooled regional assemblages are compared using the Raup and Crick index of faunal similarity; then, the inferred similarity matrices are visualized as neighbour-joining trees and by projecting the statistically significant interregional similarities and dissimilarities onto palaeogeographical maps. The inferred biogeographical patterns are analysed and discussed in the light of known palaeogeographical and palaeoclimatic events. Results, Successive time intervals with distinct biogeographical contexts are identified. Prior to c. 18 Ma (Late Oligocene and Early Miocene), a relative faunal homogeneity (high interregional connectivity) is observed all over Europe, a time when major geographical barriers and a weak climatic gradient are known. Then, from the beginning of the Middle Miocene onwards, the biogeography is marked by a significant decrease in interregional faunal affinities which matches a drastic global climatic degradation and leads, in the Late Miocene (c. 11 Ma), to a marked latitudinal pattern of small mammal distribution. In spite of a short rehomogenization around the Miocene/Pliocene boundary (6,4 Ma), the biogeography of small mammals in the mid Pliocene (c. 3 Ma) finally closely reflects the extant situation. Main conclusions, The resulting biogeographical evolutionary scheme indicates that the extant endemic situation has deep historical roots corresponding to global tectonic and climatic events acting as primary drivers of long-term changes. The correlation of biogeographical events with climatic changes emphasizes the prevalent role of the climate over geography in generating heterogeneous biogeographical patterns at the continental scale. [source] Thermal structure of the Alboran Domain in the Rif (northern Morocco) and the Western Betics (southern Spain).JOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2006Constraints from Raman spectroscopy of carbonaceous material Abstract In the Rif (northern Morocco) and the Western Betics (southern Spain), the Alboran Domain forms a complex stack of metamorphic nappes including mantle peridotites (Beni Bousera and Ronda). We present in this paper new temperature data obtained in the Alboran Domain based on Raman spectroscopy of carbonaceous material (RSCM thermometry). In the lower metamorphic nappes of the Alboran Domain (lower Sebtides,Alpujárrides) temperature ranges from > 640 °C at the base of the metapelitic sequence to 500 °C at the top. The relationships between field isotherms and nappe structure show that peak temperatures were reached during strong ductile thinning of these nappes whereas they partly postdate this main episode in the Rif. In the upper nappes of the Alboran Domain (Ghomarides,Maláguides), generally supposed to be only weakly metamorphosed, temperatures range from ,500 °C at their base down to < 330 °C at the top. This temperature gradient is consistent with progressive Cenozoic resetting of K,Ar and 40Ar,39Ar ages. These nappes were thus affected by a significant thermal metamorphism, and the available age data in the underlying Sebtides,Alpujárrides show that this metamorphism is related to the metamorphic evolution of the whole Alboran Domain during the Late Oligocene,Early Miocene. Such thermal structure and metamorphic evolution can be explained by generalized extension in the whole Alboran Domain crustal sequence. At a larger scale, the present thermal structure of the Alboran Domain is roughly spatially consistent around the Beni Bousera peridotites in the Rif, but much more affected by late brittle tectonics around the Ronda peridotites in the Western Betics. Therefore, on the basis of the observed thermal structure, the metamorphic evolution of the Alboran Domain can be interpreted as the result of the ascent of hot mantle units contemporaneous with thinning of the whole lithosphere during an Oligo-Miocene extensional event. The resulting structure has however been dismembered by late brittle tectonics in the Western Betics. [source] The radiation of the Cape flora, southern AfricaBIOLOGICAL REVIEWS, Issue 4 2003H. P. LINDER ABSTRACT The flora of the south-western tip of southern Africa, the Cape flora, with some 9000 species in an area of 90 000 km2 is much more speciose than can be expected from its area or latitude, and is comparable to that expected from the most diverse equatorial areas. The endemism of almost 70%, on the other hand, is comparable to that found on islands. This high endemism is accounted for by the ecological and geographical isolation of the Cape Floristic Region, but explanations for the high species richness are not so easily found. The high species richness is accentuated when its taxonomic distribution is investigated: almost half of the total species richness of the area is accounted for by 33,Cape floral clades'. These are clades which may have initially diversified in the region, and of which at least half the species are still found in the Cape Floristic Region. Such a high contribution by a very small number of clades is typical of island floras, not of mainland floras. The start of the radiation of these clades has been dated by molecular clock techniques to between 18 million years ago (Mya)(Pelargonium) and 8 Mya (Phylica), but only six radiations have been dated to date. The fossil evidence for the dating of the radiation is shown to be largely speculative. The Cenozoic environmental history of southern Africa is reviewed in search of possible triggers for the radiations, climatic changes emerge as the most likely candidate. Due to a very poor fossil record, the climatic history has to be inferred from larger scale patterns, these suggest large-scale fluctuations between summer wet (Palaeocene, Early Miocene)and summer dry climates (Oligocene, Middle Miocene to present). The massive speciation in the Cape flora might be accounted for by the diverse limitations to gene flow (dissected landscapes, pollinator specialisation, long flowering times allowing much phenological specialisation), as well as a richly complex environment providing a diversity of selective forces (geographically variable climate, much altitude variation, different soil types, rocky terrain providing many micro-niches, and regular fires providing both intermediate disturbances, as well as different ways of surviving the fires). However, much of this is based on correlation, and there is a great need for (a)experimental testing of the proposed speciation mechanisms, (b)more molecular clock estimates of the age and pattern of the radiations, and (c)more fossil evidence bearing on the past climates. [source] A New Fossil Termite (Isoptera, Stolotermitidae, Stolotermes) from the Early Miocene of Otago, New ZealandACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2010Uwe KAULFUSS Abstract: The forewing of a termite from Early Miocene lake sediments in Otago, southern New Zealand is figured and described. It exhibits the generic characters of the damp-wood termite Stolotermes Hägen, but differs from forewings of the known species in size and venation pattern and is described as Stolotermes kupe sp. nov. S. hupe represents the first confident record of fossil Stolotermitidae and extends the fossil record of the family back to the Early Miocene. It also is the first direct evidence of fossil Isoptera from New Zealand, though silicified termite faecal pellets, referable to Kalotermes brauni, have been previously described. S. kupe indicates that Stolotermitidae has been present in the Australasian region since at least the Early Miocene. [source] A complex, young subduction zone imaged by three-dimensional seismic velocity, Fiordland, New ZealandGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Donna Eberhart-Phillips Summary The Fiordland subduction zone, where subduction developed in the late Miocene, has been imaged with P and S,P arrival-time data from 311 earthquakes in a simultaneous inversion for hypocentres and 3-D VP and VP/VS models. The three-month microearthquake survey, recorded with 24 portable seismographs, provides excellent coverage, and, since earthquakes to depths of 130 km are included, parts of the model are well-resolved to depths of 100 km. The crustal features are generally consistent with geology. The low velocity in the upper 10 km is associated with the Te Anau and Waiau basins. The Western Fiordland Orthogneiss is associated with a prominent feature from near-surface to over 40 km depth, which includes the residue from the basaltic source rocks. It is defined by high VP (7.4 km s,1 at 15 km depth) and slightly low VP/VS, and has distinct boundaries on its southern and eastern margins. Adjacent to the deepest earthquakes, there is high-velocity Pacific mantle below 80 km depth, inferred to be the mantle expression of ongoing shortening since the early Miocene. As the subducting slab moves down and northeast, it is hindered by the high-velocity body and bends to near-vertical. Bending is accommodated by distributed fracturing evidenced by high VP/VS and persistent deep earthquake activity. Buckling of the subducted plate pushes up the Western Fiordland Orthogneiss. In the transition to the Alpine fault in northern Fiordland, a prominent low-velocity crustal root is consistent with ductile thickening in combination with downwarp of the subducted plate. [source] A dwarf species of the Phalacrocoracoidea (cormorants and anhingas) from the early Miocene of GermanyIBIS, Issue 2 2009GERALD MAYR A tarsometatarsus of a diminutive representative of the Phalacrocoracoidea, the clade including the Phalacrocoracidae (cormorants) and Anhingidae (anhingas), is described from the early Miocene of Germany. The fossil is assigned to a new species Limicorallus (?) carbunculus, and closely resembles the tarsometatarsus of extant Phalacrocoracidae in overall morphology. Limicorallus (?) carbunculus is the smallest representative of the Phalacrocoracoidea, reaching only two-thirds the size of the extant Pygmy Cormorant Phalacrocorax pygmeus. By significantly lowering the minimum size of the Phalacrocoracoidea, this new species adds to our knowledge of the early diversity of this clade. [source] Phylogeography of Cape Verde Island skinks (Mabuya)MOLECULAR ECOLOGY, Issue 6 2001R. P. Brown Abstract The Cape Verde Islands are of volcanic origin with most having appeared between the early Miocene and mid-Pleistocene. They contain six known species of Mabuya skinks. Phylogeographical relationships within and among the relatively widespread taxa M. stangeri, M. spinalis and M. delalandii were inferred, based on , 1 kbp of the cytochrome b gene (mitochondrial DNA). Reciprocal monophyly of M. spinalis and M. stangeri was established, which may have arisen from an early Pliocene/late Miocene cladogenetic event. Considerable between-island sequence divergence was detected among M. spinalis, which appears to have colonized the older islands (Sal and Boavista) first. Much lower sequence divergence was found in M. delalandii, indicating a more recent range expansion. Here, evidence points to colonization of the younger islands of Brava and Fogo soon after appearance. There are similarities between some of the described patterns and those seen in lizards from the Canary Islands. [source] Opisthobranch molluscs from the Tertiary of the Aquitaine Basin (south-western France), with descriptions of seven new species and a new genusPALAEONTOLOGY, Issue 3 2000Ángel Valdés An exceptionally well-preserved collection of Tertiary opisthobranch molluscs from the Aquitaine Basin, France, includes species of the order Notaspidea [Umbraculum sanctipaulensis sp. nov., Tylodina perversa (Gmelin), Spiricella unguiculus Rang and Des Moulins, Berthella aquitaniensis sp. nov., Berthella ateles sp. nov.], of the order Anaspidea [Akera cf. bullata Mu¨ller, Floribella corrugata (Cossmann), Floribella cossmanni sp. nov., Floribella rozieri sp. nov., Limondinia ornata gen. et sp. nov.] and of the order Sacoglossa [Volvatella faviae sp. nov.]. BerthellaaquitaniensisB. atelesV. faviae are the first fossil records of the families Volvatellidae and Pleurobranchidae. Floribella plicifera (Cossmann) and F.corrugata, originally assigned to the genus Philine, belong to the genus Floribella and constitute the oldest records of this genus. The fossil evidence indicates that in Umbraculum laudunensis and U. sanctipaulensis the shell probably covered most of the animal, whereas in the Recent U. umbraculum the shell only covers the central portion of the body. Tylodina perversa could be an old species that appeared during the early Miocene, more than 21 Ma. The Recent shells of Akera bullata are indistinguishable from fossils as old as the mid Eocene, but it may be biologically unrealistic to consider them to be the same species. The European species of Floribella evolved from the bullomorph shells of the early Eocene forms to the elongate shells of the early Miocene. The genus Volvatella is another example of marine tropical disjoint distributions and an excellent ecological indicator. [source] Olfactory fossa of Tremacebus harringtoni (platyrrhini, early Miocene, Sacanana, Argentina): Implications for activity patternTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 1 2004Richard F. Kay Abstract CT imaging was undertaken on the skull of , 20-Myr-old Miocene Tremacebus harringtoni. Here we report our observations on the relative size of the olfactory fossa and its implications for the behavior of Tremacebus. The endocranial surface of Tremacebus is incomplete, making precise estimate of brain size and olfactory fossa size imprecise. However, olfactory fossa breadth and maximum endocranial breadth measured from CT images of one catarrhine species and eight platyrrhine species for which volumes of the olfactory bulb and brain are known show that the osteological proxies give a reasonably accurate indication of relative olfactory bulb size. Nocturnal Aotus has the largest relative olfactory fossa breadth and the largest olfactory bulb volume compared to brain volume among extant anthropoids. Tremacebus had a much smaller olfactory fossa breadth and, by inference, bulb volume,within the range of our sample of diurnal anthropoids. Variations in the relative size of the olfactory bulbs in platyrrhines appear to relate to the importance of olfaction in daily behaviors. Aotus has the largest olfactory bulbs among platyrrhines and relies more on olfactory cues when foraging than Cebus, Callicebus, or Saguinus. As in other examples of nocturnal versus diurnal primates, nocturnality may have been the environmental factor that selected for this difference in Aotus, although communication and other behaviors are also likely to select for olfactory variation in diurnal anthropoids. Considering the olfactory fossa size of Tremacebus, olfactory ability of this Miocene monkey was probably not as sensitive as in Aotus and counts against the hypothesis that Tremacebus was nocturnal. This finding accords well with previous observations that the orbits of Tremacebus are not as large as nocturnal Aotus. © 2004 Wiley-Liss, Inc. [source] Insights in the exhumation history of the NW Zagros from bedrock and detrital apatite fission-track analysis: evidence for a long-lived orogenyBASIN RESEARCH, Issue 5 2010Stéphane Homke ABSTRACT We present the first fission-track (FT) thermochronology results for the NW Zagros Belt (SW Iran) in order to identify denudation episodes that occurred during the protracted Zagros orogeny. Samples were collected from the two main detrital successions of the NW Zagros foreland basin: the Palaeocene,early Eocene Amiran,Kashkan succession and the Miocene Agha Jari and Bakhtyari Formations. In situ bedrock samples were furthermore collected in the Sanandaj-Sirjan Zone. Only apatite fission-track (AFT) data have been successfully obtained, including 26 ages and 11 track-length distributions. Five families of AFT ages have been documented from analyses of in situ bedrock and detrital samples: pre-middle Jurassic at ,171 and ,225 Ma, early,late Cretaceous at ,91 Ma, Maastrichtian at ,66 Ma, middle,late Eocene at ,38 Ma and Oligocene,early Miocene at ,22 Ma. The most widespread middle,late Eocene cooling phase, around ,38 Ma, is documented by a predominant grain-age population in Agha Jari sediments and by cooling ages of a granitic boulder sample. AFT ages document at least three cooling/denudation periods linked to major geodynamic events related to the Zagros orogeny, during the late Cretaceous oceanic obduction event, during the middle and late Eocene and during the early Miocene. Both late Cretaceous and early Miocene orogenic processes produced bending of the Arabian plate and concomitant foreland deposition. Between the two major flexural foreland episodes, the middle,late Eocene phase mostly produced a long-lasting slow- or nondepositional episode in the inner part of the foreland basin, whereas deposition and tectonics migrated to the NE along the Sanandaj-Sirjan domain and its Gaveh Rud fore-arc basin. As evidenced in this study, the Zagros orogeny was long-lived and multi-episodic, implying that the timing of accretion of the different tectonic domains that form the Zagros Mountains requires cautious interpretation. [source] Evolution of basin architecture in an incipient continental rift: the Cenozoic Most Basin, Eger Graben (Central Europe)BASIN RESEARCH, Issue 3 2009Michal Rajchl ABSTRACT The Oligo-Miocene Most Basin is the largest preserved sedimentary basin within the Eger Graben, the easternmost part of the European Cenozoic Rift System (ECRIS). The basin is interpreted as a part of an incipient rift system that underwent two distinct phases of extension. The first phase, characterised by NNE,SSW- to N,S-oriented horizontal extension between the end of Eocene and early Miocene, was oblique to the rift axis and caused evolution of a fault system characterised by en-échelon-arranged E,W (ENE,WSW) faults. These faults defined a number of small, shallow initial depocentres of very small subsidence rates that gradually merged during the growth and linkage of the normal fault segments. The youngest part of the basin fill indicates accelerated subsidence caused probably by the concentration of displacement at several major bounding faults. Major post-depositional faulting and forced folding were related to a change in the extension vector to an orthogonal position with respect to the rift axis and overprinting of the E,W faults by an NE,SW normal fault system. The origin of the palaeostress field of the earlier, oblique, extensional phase remains controversial and can be attributed either to the effects of the Alpine lithospheric root or (perhaps more likely because of the dominant volcanism at the onset of Eger Graben formation) to doming due to thermal perturbation of the lithosphere. The later, orthogonal, extensional phase is explained by stretching along the crest of a growing regional-scale anticlinal feature, which supports the recent hypothesis of lithospheric folding in the Alpine,Carpathian foreland. [source] Carbonate seismic stratigraphy of the Gulf of Papua mixed depositional system: Neogene stratigraphic signature and eustatic controlBASIN RESEARCH, Issue 2 2008Evgueni N. Tcherepanov ABSTRACT The Eocene,Miocene carbonate deposition in the Gulf of Papua (GoP) corresponds to the carbonate evolution phase of this continental margin mixed depositional system. Global sea-level (eustatic) fluctuations appear to have been the most important factor influencing the mixed depositional system development during its carbonate phase. Development of the major carbonate system in the Gulf was initiated during the Eocene. Subsequent to an early Oligocene hiatus, the carbonate system expanded its surface area, vertically aggraded, then systematically backstepped, and finally partially drowned during the late Oligocene,early part of the early Miocene. During the late early Miocene,early middle Miocene, the carbonate system continued its vertical growth in most platform areas, where it was able to keep up with sea-level rise. At the early middle/late middle Miocene (Langhian/Serravallian) boundary, carbonate deposition shifted downward during a long-term sea-level regression, exposing most of the early middle Miocene platform tops. Following this downward shift, active carbonate production became restricted during the late middle Miocene to only the northeastern part of the study area, and carbonate accumulation was characterized by four systematically prograding units. At the very beginning of the late Miocene, the platform tops were re-flooded. The carbonate system was partially drowned, systematically backstepped, and locally aggraded during part of the late Miocene, the early Pliocene, and the Quaternary. The overall organization of the carbonate sequence geometries, observed in the GoP, display a clear pattern, often referred to as the Oligocene,Neogene stratigraphic signature. This pattern is identical to contemporaneous sedimentary patterns observed in pure carbonate systems such as in the Maldives and in the Bahamas, and also in some siliciclastic systems. Because this pattern is observed in several globally distributed locations, the recognition of the Oligocene,Neogene stratigraphic signature in the GoP demonstrates that the depositional evolution during the late Oligocene,Miocene and the early Pliocene must have been dominantly controlled by eustatic fluctuations. [source] Molecular phylogeny of icefish Salangidae based on complete mtDNA cytochrome b sequences, with comments on estuarine fish evolutionBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2007JIE ZHANG Phylogenetic relationships among 15 species in the family Salangidae were constructed based on the complete cytochrome b sequence (1141 bp). We confirmed the monophyly of the family Salangidae and defined four primitive lineages within this family: (I) Protosalanx, Neosalanx anderssoni, Neosalanx tangkahkeii, and Neosalanx argentea; (II) Neosalanx reganius, Neosalanx jordani, Neosalanx oligodontis, and Neosalanx sp.; (III) Hemisalanx, Salanx, Leucosoma, and Salangichthys ishikawae; and (IV) Salangichthys microdon. A major finding of our study is the key basal placement of Sg. microdon. According to the tentative estimation, the divergence of the four lineages appears to have been initiated in the early Miocene (21 Mya), with most speciation events occurring 1.05,9.90 Mya. Taxonomic revisions on subfamilial, generic, and specific levels were carried out based on phylogenetic relationships and genetic distance, taking into account some key morphological characters. The speciation mechanism in Salangidae is also discussed, and the evidence shows that geographical isolation, water mass, as well as some ecological factors, may not always play important roles in the speciation of temperate estuarine fish. In the most cases, sympatric salangids are not monophyletic, indicating that their coexistence reflects secondary contact rather than sympatric speciation. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 327,342. [source] Innovation and evolution at the edge: origins and fates of gastropods with a labral toothBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2001GÉERAT J. VERMEIJ I combined data from the taxonomy, phytogeny, functional morphology, biogeography, and fossil record of gastropods to probe the origins, distribution, and fates of predatory gastropod clades characterized by the presence of a labral tooth, a downwardly projecting tooth or spine formed at the edge of the outer lip of the shell. A labral tooth occurs in at least 608 species, of which 251 are Recent. Studies of the type and position of the labral tooth, along with other characters, indicate that the labral tooth has evolved independently at least 58 times, beginning in the Campanian epoch of the late Cretaceous. The labral tooth plays a more or less active part in predation on relatively large prey animals that are protected by a hard skeleton. In the Recent fauna, tooth-bearing species are overwhelmingly warm-temperate to tropical in distribution (240 of 251 species; 96%). Within Muricidae (excluding Coralliophilinae), however, there is no discernible latitudinal gradient in the number of tooth-bearing species relative to total regional diversity. First appearances of clades with a labral tooth are overwhelmingly concentrated in the late Oligocene to Pleistocene interval, with the largest number appearing during the early Miocene (12 clades). The temporal pattern differs significantly from that expected on the basis of the number of faunas available per time interval, and is therefore not an artifact of sampling or fossil preservation. The most consistent factor associated with, and permitting the repeated evolution of, the labral tooth is high planktonic primary productivity. Two factors may account for the link between primary productivity and the evolution of labral téeth: (1) the general economic opportunity afforded by ready availability of an access to nutrients, and (2) the greater abundance and sizes range of available suspension-féeding prey animals. Incumbency,the presence of already well-adapted species,often controls evolutionary opportunity. The complementary distributions of major tooth-bearing clades in many parts of the world point to the role of well-adapted incumbents in limiting the adaptive exploration by other clades that could in principle evolve a labral tooth. The elimination of incumbents by extinction, however, does not provide opportunities for other clades to fill the adaptive void. [source] | |||||||||||||