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An Oligocene microthermal forest dominated by Nothofagus in Sierra Baguales, Chilean Patagonia: Response to global cooling and tectonic events
... The fossil record of the formation, on the Argentinean side, includes silicified woods (Pujana, 2007(Pujana, , 2008(Pujana, , 2009a(Pujana, , 2009b, leaves (Frenguelli, 1941;Césari et al., 2015;Caviglia and Pujana, 2020), fungal decay (Greppi et al., 2018), spores and pollen grains (Barreda et al., 2009). On the Chilean side, it includes silicified woods (Torres et al., 2013;Torre et al., 2016) and leaves (Torres et al., 2013;Torres et al., 2016;Gutiérrez et al., 2019). ...
... A fossil leaf assemblage from the Río Leona Formation in Chilean Patagonia was recently studied by Gutiérrez et al. (2019). The authors used the leaf margin analysis model proposed by Hinojosa et al. (2011) for South America and the global model of Peppe et al. (2011) to estimate MAT. ...
... Analysis of fossil leaves from the Río Leona Formation in Chile made by Gutiérrez et al. (2019) gave an estimated MAP of 93.1 (− 89.1 + 98.1) cm/year (with the Univariate Precipitation Model; Hinojosa, 2005) and 82.2 (±46.9) (with CLAMP; Wolfe, 1993). ...
Patagonia has a rich record of fossil woods that are a unique data store of paleoclimatic information. We studied the wood flora recovered from the Río Leona Formation (early Miocene) of southern Patagonia near El Calafate and Río Turbio localities, Santa Cruz Province, Argentina. The fossil wood assemblage was analyzed using various methodologies (anatomy analysis, Vulnerability and Mesomorphic indices, and the Coexistence Approach) to determine paleoclimate variables including mean annual temperature (MAT) and mean annual precipitation (MAP). The anatomy analysis developed by Wiemann et al. (1998, 1999) is based mostly on woods from the Northern Hemisphere. We applied those equations to extant woods from the southernmost region of South America to test their functionality and to compare them with the results obtained from the fossils. These equations gave limited results. Climate signals from fossil woods suggest a microthermal climate for the region with MAT of 8–12 °C and MAP of 80–170 cm/year. In addition, part of the results points towards an environment with water in abundance (i.e., Coexistence Approach and some wood characters influenced by the environment) and other results suggest wood tolerance to hydric stress (i.e., Vulnerability Index, Mesomorphy Index, and wood characters influenced by the environment). These suggest an environment with rainy and dry seasons, which is also supported by the presence of well-marked growth ring boundaries and false rings. These conditions can be found today in central Chile, a region that shares some vegetation elements with the Río Leona Formation and has a Mediterranean climate.
... Paleobotanists have used fossil plants as proxies for estimating past climate variables at different geological times (Hinojosa et al. 2006a;Arens & Harris 2015;Caviglia 2018;Lowe et al. 2018;Gutiérrez et al. 2019). Estimates of the past climate conditions are derived from present-day calibration data set as close as possible to the climate response of the studied fossil leaves (Wolfe 1993;Jordan 1997;Gregory-Wodzicki 2000;Jacobs 2002;Greenwood et al. 2004 among others). ...
... The early-middle Eocene was characterized by warm and humid conditions with a high diversity of fossil plants (Wilf et al. 2005). During the middle-late Eocene a mixed paleoflora evolved in Patagonia under warmer conditions (Romero 1978(Romero , 1986Hinojosa & Villagrán 1997) composed of paratropical and cold temperate fossil species (Romero 1986;Hinojosa & Villagrán 1997;Iglesias et al. 2011;Vento et al. 2017;Vento & Prámparo 2018;Gutiérrez et al. 2019). ...
... A global climate deterioration with temperate cool conditions in the early Oligocene is reflected by changes in floral composition (Wilf et al. 2003;Bowen 2007;Gutiérrez et al. 2019). The vegetation changed from paratropical to a colder temperate biome with temperate-cool representatives Vento et al. 2017;Gutiérrez et al. 2019). ...
It is widely recognized that fossil leaves are good proxies for paleoclimate estimates, and leaf physiognomy analysis is a traditional technique used to make climate estimates. There are only a few paleoclimate reconstructions for the southern part of South America based on this technique. Here we report climate parameters using fossil leaves from the Río Turbio (Eocene-Oligocene) and Río Guillermo (Oligocene-early Miocene?) formations in southern South America, Cuenca Austral, Argentina. We used univariate (leaf margin and leaf foliar area analysis) and multivariate methods (CLAMP, DiLP) on two datasets from South America, in the Southern Hemisphere. Lower and upper members of the Río Turbio Formation show a mixed paleoflora represented by paratropical as well as cool-temperate taxa such as Nothofagus, with a similar percentage of untoothed fossil leaves. Climate estimates indicate warm and humid conditions for both Río Turbio Formation members. The Río Guillermo Formation is represented by mostly cool-temperate elements, mainly Nothofagus, and most with toothed margins. The paleoclimate analysis indicates a decrease in temperature and precipitation when comparing the two studied formations. Today, temperate forests in southern Argentina have a plant composition and climate more similar to the estimates made for the Río Guillermo Formation.
In the southeastern corner of the Isla Grande of Tierra del Fuego, southernmost Argentina, small
outcrops representing Late Eocene-Early Oligocene sedimentation in fluvial environments, are referred to
the Sloggett Formation. This unit crops out along the shores of Bahía Sloggett, where it is represented by
carbonaceous mudstones, sandstones and conglomerates. A new paleofloristic collection of this site, originally
reported by Andersson at the beginning of the 20th, was collected and analyzed, revealing the presence
of gymnosperm and angiosperm leaves. Conifers are represented by probable Podocarpaceae and
the presence of Araucariaceae is confirmed by leaves with preserved anatomy. Angiosperms, although
fragmentary, have been grouped in morphotypes, which are referred to the Nothofagaceae, Myrtaceae
and Lauraceae. The Sloggett paleoflora is similar in composition to other contemporary floras, described
from southern South America and that originated in temperate to cold-temperate and humid forest.
The origins of South America’s exceptional plant diversity are poorly known from the fossil record. We report on unbiased quantitative collections of fossil floras from Laguna del Hunco (LH) and Río Pichileufú (RP) in Patagonia, Argentina. These sites represent a frost‐free humid biome in South American middle latitudes of the globally warm Eocene. At LH, from 4,303 identified specimens, we recognize 186 species of plant organs and 152 species of leaves. Adjusted for sample size, the LH flora is more diverse than comparable Eocene floras known from other continents. The RP flora shares several taxa with LH and appears to be as rich, although sampling is preliminary. The two floras were previously considered coeval. However, 40Ar/39Ar dating of three ash‐fall tuff beds in close stratigraphic association with the RP flora indicates an age of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $47.46\pm 0.05$ \end{document} Ma, 4.5 million years younger than LH, for which one tuff is reanalyzed here as \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $51.91\pm 0.22$ \end{document} Ma. Thus, diverse floral associations in Patagonia evolved by the Eocene, possibly in response to global warming, and were persistent and areally extensive. This suggests extraordinary richness at low latitudes via the latitudinal diversity gradient, corroborated by published palynological data from the Eocene of Colombia.
Aim
We used fossil and phylogenetic evidence to reconstruct climatic niche evolution in Nothofagus , a Gondwana genus distributed in tropical and temperate latitudes. To assess whether the modern distribution of the genus can be explained by the tropical conservatism hypothesis, we tested three predictions: (1) species from all Nothofagus subgenera coexisted under mesothermal climates during the early Eocene; (2) tolerance to microthermal climates evolved during the Eocene–Oligocene cooling from an ancestor that grew under mesothermal conditions; and (3) the climatic niche in Nothofagus is phylogenetically conserved.
Location
Australia, New Zealand, New Caledonia, Papua‐New Guinea and South America.
Methods
We estimated the palaeoclimate of the Early Eocene, fossil‐bearing Ligorio Marquez Formation ( LMF , Chile), using coexistence and leaf physiognomic analysis. We reconstructed ancestral climatic niches of Nothofagus using extant species distributions and a time‐calibrated phylogeny. Finally, we used the morphological disparity index and phylogenetic generalized least squares to assess whether climatic variables follow a Brownian motion ( BM ) or an Ornstein–Uhlenbeck ( OU ) model of evolution.
Results
Our palaeoclimatic estimates suggest mesothermal conditions for the LMF , where macrofossils associated with subgenera Lophozonia and possibly Fuscospora, and fossil pollen of Brassospora and Fuscospora / Nothofagus were recorded. These results are not supported by our phylogenetic analysis, which instead suggests that the ancestor of Nothofagus lived under microthermal to marginally mesothermal conditions, with tolerance to mesothermal conditions evolving only in the subgenus Brassospor a. Precipitation and temperature dimensions of the realized climatic niche fit with a gradual BM or constrained OU model of evolution.
Main Conclusions
Our results suggest that the use of phylogenetic reconstruction methods based only on present distributions of extant taxa to infer ancestral climatic niches is likely to lead to erroneous results when climatic requirements of ancestors differ from their extant descendants, or when much extinction has occurred.
We present the case that the fossil record of Nothofagaceae, which is much more extensive in terms of species numbers than the living species, cannot be dealt with in a productive way by the recent proposal by Heenan and Smissen to split Nothofagus into four genera (Phytotaxa, vol. 146, http://dx.doi.org/10.11646/phytotaxa.146.1.1). Such a proposal will render the fossil record almost unworkable, and will lead to a major split in the approach taken by palynologists in comparison to other researchers. We believe the case for the new generic names, while valid, is weak, and is far outweighed by the utility of retaining Nothofagus sensu lato.
A floral change occurring in northern South America at the Paleocene/Eocene boundary is analysed using palynological data. The sequence studied is an outcrop from the Venezuelan Maracaibo basin, deposited in shallow marine to coastal environments without apparent stratigraphic breaks. Significant pollen and spore counts from 237 samples were studied stratigraphically and statistically in order to compare Paleocene and Eocene palaeofloras and palaeoecological trends. The Late Paleocene/Early Eocene transition is the boundary between two floras which differ both qualitatively and quantitatively. However, the change is not sudden but stepped and gradual. Paleocene taxa seem to be of pantropical distribution, whereas Eocene assemblages are more restricted to the Neotropics. The global warming well documented elsewhere is proposed as the major cause for these changes. Trends in sporomorph diversity in this record appear to track changes in temperature documented in isotopic records from temperate regions. The extinct parent plant of Echitriporites trianguliformis is tentatively proposed to be intolerant to high temperatures, because of its absence during the Early Eocene warm phase. Palaeoecologically, although marsh and back-mangrove swamps dominated both Late Paleocene and Early Eocene assemblages, their taxonomic compositions were different, especially in the inland marsh forests. Mangrove components are scarce or absent through the whole sequence studied, suggesting the absence of these communities during the time-interval analysed. A palaeoecological subdivision into assemblage zones was not possible; instead, a recurrent pattern suggesting palynological cycles was observed. However, palynocycles could not be studied in detail due to the lack of knowledge of botanical affinities for many of the taxa involved and the apparent absence of mangrove assemblages.
Synthesis of the stratigraphy and geology of the southern Andes (47 -. 51 S lat.)
A late Oligocene plant macrofossil assemblage is described from the Río Leona Formation, Argentinian Patagonia. This includes a fern, “Blechnum” turbioense Frenguelli, one species of conifer, and sixteen angiosperm taxa. Rosaceae, Myrtaceae, Proteaceae, Lauraceae, Anacardiaceae and Typhaceae are represented by one species in each family. Five species are considered to be members of the Fabales. Three leaf taxa together with Carpolithus seeds are placed in the Nothofagaceae. Palynomorphs and permineralized woods complete the floral record of the Río Leona Formation, which is considered early late Oligocene based on radiometric dating and palynofloras.
A late Oligocene plantmacrofossil assemblage is described fromthe Río Leona Formation, Argentinian Patagonia. This includes a fern, “Blechnum” turbioense Frenguelli, one species of conifer, and sixteen angiosperm taxa. Rosaceae, Myrtaceae, Proteaceae, Lauraceae, Anacardiaceae and Typhaceae are represented by one species in each family. Five species are considered to be members of the Fabales. Three leaf taxa together with Carpolithus seeds are placed in the Nothofagaceae. Palynomorphs and permineralized woods complete the floral record of the Río Leona Formation,which is considered early late Oligocene based on radiometric dating and palynofloras. http://dx.doi.org/10.1016/j.revpalbo.2015.01.002
The statistical analysis of published Paleocene–Late Miocene palynological data from Patagonia supports several major stages of vegetation. These stages represent distinctive floral assemblages, both in composition and structure. Detrended correspondence analysis shows that during the Paleocene, southern South America was dominated by Australasian, Neotropical and Pantropical phytogeographical elements (Gondwanic paleoflora). The climate was warm and very humid. The Early Eocene was dominated by Neotropical and Pantropical taxa (Subtropical Gondwanic Paleoflora) and a reduced proportion of Australasian and a low proportion of Antarctic elements. The Middle Eocene and Oligocene were characterized by the ‘Mixed Paleoflora’ with the exception of the Sloggett Formation. The climate was less humid due to the onset of the Antarctic glaciation. The presence of Antarctic palynomorphs (Nothofagaceae, Podocarpaceae, Proteaceae) in Patagonia is consistent with the global cooling trend during the Late Eocene and Early Oligocene. By the Late Oligocene–Early Miocene, warm climates allowed the southward dispersal of Neotropical elements (palms, Cupania, Alchornea, Rubiaceae, Combretaceae), adding megathermal elements to the local Gondwanic floras. The appearance of some Neotropical families (Symplocaceae, Euphorbiaceae Alchornea) may indicate the Late Oligocene global warming event. The rise of xerophytic and halophytic shrubby-herbaceous elements (Convolvulaceae, Asteraceae, Poaceae, Chenopodiaceae and Ephedraceae) during the Late Oligocene, becoming more abundant during the Early Miocene began to give a modern appearance to plant communities. The Early–Middle Miocene corresponds to the Transitional Paleophytogeoprovince of central and southeastern Argentina, defined by a mix of Neotropical and Austral components. The Middle–Late Miocene was characterized by the final demise of megathermal elements in Patagonia, coupled with an increasing diversity and abundance of xerophytic adapted taxa, including Asteraceae, Chenopodiaceae and Convolvulaceae. Late Miocene vegetation was similar to the present vegetation, with the steppe expanded across extra-Andean Patagonia and the forest restricted to western areas where rainfall was still abundant.
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Premise of study:
Have Gondwanan rainforest floral associations survived? Where do they occur today? Have they survived continuously in particular locations? How significant is their living floristic signal? We revisit these classic questions in light of significant recent increases in relevant paleobotanical data.•
Methods:
We traced the extinction and persistence of lineages and associations through the past across four now separated regions-Australia, New Zealand, Patagonia, and Antarctica-using fossil occurrence data from 63 well-dated Gondwanan rainforest sites and 396 constituent taxa. Fossil sites were allocated to four age groups: Cretaceous, Paleocene-Eocene, Neogene plus Oligocene, and Pleistocene. We compared the modern and ancient distributions of lineages represented in the fossil record to see if dissimilarity increased with time. We quantified similarity-dissimilarity of composition and taxonomic structure among fossil assemblages, and between fossil and modern assemblages.•
Key results:
Strong similarities between ancient Patagonia and Australia confirmed shared Gondwanan rainforest history, but more of the lineages persisted in Australia. Samples of ancient Australia grouped with the extant floras of Australia, New Guinea, New Caledonia, Fiji, and Mt. Kinabalu. Decreasing similarity through time among the regional floras of Antarctica, Patagonia, New Zealand, and southern Australia reflects multiple extinction events.•
Conclusions:
Gondwanan rainforest lineages contribute significantly to modern rainforest community assembly and often co-occur in widely separated assemblages far from their early fossil records. Understanding how and where lineages from ancient Gondwanan assemblages co-occur today has implications for the conservation of global rainforest vegetation, including in the Old World tropics.
In this chapter we use the plant macrofossil record as evidence of past ecosystems, and in particular the record from south-eastern Australia. We provide background on the evolution of Australian tropical rainforests over the Tertiary Period (65 to 1.8 million years ago), and we consider the origin of Australian tropical rainforests, how they responded to climatic and other environmental factors over geological time, and the ecological processes that have shaped them in the crucible of continental drift and climatic deterioration.
The age of the Navidad Formation in central Chile has always been controversial, mainly due to the conflicting age ranges indicated by its macro- and microfossils. Macrofossils are generally interpreted as having been reworked from older, Early to Middle Miocene strata, whereas a Late Miocene-Pliocene age has been accepted on the basis of planktonic foraminifer index species. The results of this study, however, indicate that the macrofossils occur in situ, which necessitates a complete revision of the geochronological data. It is concluded that the evidence for an Early to Middle Miocene age is overwhelming, and that the planktonic foraminifer index species must have appeared in the SE Pacific earlier than elsewhere. These include Globoturborotalia apertura, Globorotalia puncticulata (Deshayes), Globorotalia spheriomizea (Walters), Neogloboquadrina pachyderma (Ehrenberg), and Neogloboquadrina acostaensis (Blow). An Early to Middle Miocene age for the Navidad Formation correlates well with a reinterpretation of its depositional environment as a continental shelf instead of a deepwater continental slope, global and regional paleoclimatic events, and the tectonic development of the Andes Range.
The generic taxonomy of the Nothofagaceae is revised. We present a new phylogenetic analysis of morphological
characters and map these characters onto a recently published phylogenetic tree obtained from DNA sequence data. Results of these and previous analyses strongly support the monophyly of four clades of Nothofagaceae that are currently treated as subgenera of Nothofagus. The four clades of Nothofagaceae are robust and well-supported, with deep stem divergences, have evolutionary equivalence with other genera of Fagales, and can be circumscribed with morphological characters. We argue that these morphological and molecular differences are sufficient for the four clades of Nothofagaceae to be recognised at the primary rank of genus, and that this classification will be more informative and efficient than the currently circumscribed Nothofagus with four subgenera.
Nothofagus is recircumscribed to include five species from southern South America, Lophozonia and Trisyngyne are reinstated, and the new genus Fuscospora is described. Fuscospora and Lophozonia, with six and seven species respectively, occur in New Zealand, southern South America and Australia. Trisyngyne comprises 25 species from New Caledonia, Papua New Guinea and Indonesia. New combinations are provided where necessary in each of these genera.
Estimates of past precipitation are of broad interest for many areas of inquiry, including reconstructions of past environments and topography, climate modeling, and ocean circulation studies. The shapes and sizes of living leaves are highly sensitive to moisture conditions, and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators. Most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations. However, when tested on extant forests, this method has consistently overestimated precipitation. We present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set. The significant relationship that results, in addition to having value for paleoclimatic reconstruction, refines understanding of the long-observed positive relationship between leaf area and precipitation. Seven precipitation estimates for the Eocene of the Western United States are revised as lower than previously published but remain far wetter than the same areas today. Abundant moisture may have been an important factor in maintaining warm, frost-free conditions in the Eocene because of the major role of water vapor in retaining and transporting atmospheric heat.
En este trabajo se estudió la hibridación entre Nothofagus pumilio y N. antarctica mediante análisis de morfología foliar y de electroforesis isoenzimática en la población de altura de Laguna Negra en el noroeste de la Patagonia, Argentina. Muestras colectadas en esta población para análisis morfológicos y genéticos fueron comparadas con poblaciones puras de N. antarctica y N. pumilio. Las especies puras resultaron estadísticamente diferentes entre sí para las variables morfológicas, y el análisis multivariado mostró un patrón de agrupamiento de los híbridos con N. antarctica. El polimorfismo para 13 loci en Laguna Negra fue del 61% y resultó mayor que el de N. antarctica y N. pumilio (58 y 43% respectivamente). Se encontraron alelos diagnósticos de las especies puras y los híbridos resultaron más similares a N. antarctica. Estos resultados indican que ocurre hibridación natural entre N. antarctica y N. pumilio en la población Laguna Negra y la existencia de posibles eventos de introgresión hacia N. antarctica.
Geochronology and paleotopographic reconstruction of the porphyry-copper deposit at La Escondida, Chile, are used to calculate long-term erosion rates and to deduce the timing of Tertiary climatic change for a portion of the Atacama Desert region. Hypogene hydrothermal alteration and protore mineralization at La Escondida took place between 33.7 ± 1.4 and 31.0 ± 1.4 Ma based on K-Ar dating of hydrothermal biotite and sericite. Supergene weathering and copper-sulfide en-richment processes were active from 18.0 ± 0.7 to 14.7 ± 0.6 Ma based on K-Ar dating of supergene alunite, distinguished from hypogene alunite by grain size, color, and sulfur isotopic composition. Reworked lenses of volcanic ash in the vicinity of La Escondida provide useful time-stratigraphic markers at 8.7 ± 0.4, 6.5 ± 0.2, and 4.2 ± 0.2 Ma within present soil profiles. Long-term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at La Escondida using mass-balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid-inclusion geobarometry at similar deposits. The observed trend of decreasing long-term average erosion rates with time is consistent with arid to semiarid conditions in the early Miocene changing to hyperarid conditions during the middle Miocene. This climatic desiccation caused termination of significant supergene copper-suffide enrichment at La Escondida and elsewhere in the Atacama region and preservation of surficial features, including the ash horizons and the leached capping. Middle Miocene climatic desiccation in northern Chile and southern Peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral Humboldt Current and an increase in upwelling intensity as the Antarctic ice cap became established at approximately 15 to 13 Ma. The Central Andes Cordillera, which now provides a rain shadow protecting the Atacama region from precipitation from the east, must have attained at least half its present elevation prior to about 15 Ma to have played a similar role in the middle Miocene.
Few South American macrofloras of Paleocene age are known, and this
limits our knowledge of diversity and composition between the
end-Cretaceous event and the Eocene appearance of high floral diversity.
We report new, unbiased collections of 2516 compression specimens from
the Paleocene Salamanca Formation (ca. 61.7 Ma) from two localities in
the Palacio de los Loros exposures in southern Chubut, Patagonia,
Argentina. Our samples reveal considerably greater richness than was
previously known from the Paleocene of Patagonia, including 36 species
of angiosperm leaves as well as angiosperm fruits, flowers, and seeds;
ferns; and conifer leaves, cones, and seeds. The floras, which are from
siltstone and sandstone channel-fills deposited on low-relief floodplain
landscapes in a humid, warm temperate climate, are climatically and
paleoenvironmentally comparable to many quantitatively collected
Paleocene floras from the Western Interior of North America. Adjusted
for sample size, there are >50% more species at each Palacio de los
Loros quarry than in any comparable U.S. Paleocene sample. These results
indicate more vibrant terrestrial ecosystems in Patagonian than in North
American floodplain environments ˜4 m.y. after the end-Cretaceous
extinction, and they push back the time line 10 m.y. for the evolution
of high floral diversity in South America. The cause of the dis parity
is unknown but could involve reduced impact effects because of greater
distance from the Chicxulub site, higher latest Cretaceous diversity, or
faster recovery or immigration rates.
A cladistic analysis of Nothofagus is presented. Comparison of potential outgroups (Fagus and Betulaceae) suggests that Fagus is most satisfactory, but clear morphological differences between it and Nothofagus support the placement of the latter in the monogeneric family Nothofagaceae. The cladistic analysis supports the four subgenera and four extant pollen groups proposed in the most recent revisions and is consistent with the extensive fossil record, although not especially supported by it. The evolution of the deciduous or evergreen habit. so long considered a singular event of importance in Nothofagus, probably occurred several times, and is an example of parallel evolution. Resolution within subgenera is not high in most cases, but subgenus Lophozonia offers a particularly interesting insight into the relationship among extant species and the role of rare long distance dispersal across significant ocean barriers in Nothofagus biogeography. More data are required to refine the phylogeny.
Precise estimates of past temperatures are critical for understanding the evolution of organisms and the physical biosphere, and data from continental areas are an indispensable com- plement to the marine record of stable isotopes. Climate is considered to be a primary selective force on leaf morphology, and two widely used methods exist for estimating past mean annual temperatures from assemblages of fossil leaves. The first approach, Leaf Margin Analysis, is uni- variate, based on the positive correlation in modern forests between mean annual temperature and the proportion of species in a flora with untoothed leaf margins. The second approach, known as the Climate-Leaf Analysis Multivariate Program, is based on a modern data set that is multivariate. I argue here that the simpler, univariate approach will give paleotemperature estimates at least as precise as the multivariate method because (1) the temperature signal in the multivariate data set is dominated by the leaf-margin character; (2) the additional characters add minimal statistical precision and in practical use do not appear to improve the quality of the estimate; (3) the predictor samples in the univariate data set contain at least twice as many species as those in the multivariate data set; and (4) the presence of numerous sites in the multivariate data set that are both dry and extremely cold depresses temperature estimates for moist and nonfrigid paleofloras by about 2 8C, unless the dry and cold sites are excluded from the predictor set. New data from Western Hemisphere forests are used to test the univariate and multivariate meth- ods and to compare observed vs. predicted error distributions for temperature estimates as a func- tion of species richness. Leaf Margin Analysis provides excellent estimates of mean annual tem- perature for nine floral samples. Estimated temperatures given by 16 floral subsamples are very close both to actual temperatures and to the estimates from the samples. Temperature estimates based on the multivariate data set for four of the subsamples were generally less accurate than the estimates from Leaf Margin Analysis. Leaf-margin data from 45 transect collections demonstrate that sampling of low-diversity floras at extremely local scales can result in biased leaf-margin per- centages because species abundance patterns are uneven. For climate analysis, both modern and fossil floras should be sampled over an area sufficient to minimize this bias and to maximize re- covered species richness within a given climate.
Precise estimates of past temperatures are critical for understanding the evolution of organisms and the physical biosphere, and data from continental areas are an indispensable complement to the marine record of stable isotopes. Climate is considered to be a primary selective force on leaf morphology, and two widely used methods exist for estimating past mean annual temperatures from assemblages of fossil leaves. The first approach, Leaf Margin Analysis, is univariate, based on the positive correlation in modern forests between mean annual temperature and the proportion of species in a flora with untoothed leaf margins. The second approach, known as the Climate-Leaf Analysis Multivariate Program, is based on a modern data set that is multivariate. I argue here that the simpler, univariate approach will give paleotemperature estimates at least as precise as the multivariate method because (1) the temperature signal in the multivariate data set is dominated by the leaf-margin character; (2) the additional characters add minimal statistical precision and in practical use do not appear to improve the quality of the estimate; (3) the predictor samples in the univariate data set contain at least twice as many species as those in the multivariate data set; and (4) the presence of numerous sites in the multivariate data set that are both dry and extremely cold depresses temperature estimates for moist and nonfrigid paleofloras by about 2°C, unless the dry and cold sites are excluded from the predictor set. New data from Western Hemisphere forests are used to test the univariate and multivariate methods and to compare observed vs. predicted error distributions for temperature estimates as a function of species richness. Leaf Margin Analysis provides excellent estimates of mean annual temperature for nine floral samples. Estimated temperatures given by 16 floral subsamples are very close both to actual temperatures and to the estimates from the samples. Temperature estimates based on the multivariate data set for four of the subsamples were generally less accurate than the estimates from Leaf Margin Analysis. Leaf-margin data from 45 transect collections demonstrate that sampling of low-diversity floras at extremely local scales can result in biased leaf-margin percentages because species abundance patterns are uneven. For climate analysis, both modern and fossil floras should be sampled over an area sufficient to minimize this bias and to maximize recovered species richness within a given climate.
The Sierra Baguales, situated north of the Torres Del Paine National Park in the Magallanes region of southern Chile, shows a well-exposed stratigraphic sequence ranging from the Late Cretaceous to late Pliocene, which presents a unique opportunity to study the evolution of sedimentological styles and trends, palaeoclimate changes, and tectonic events during this period. The depositional environment changed from a continental slope and shelf during the Cenomanian-Campanian (Tres Pasos Formation) to deltaic between the Campanian-Maastrichtian (Dorotea Formation) and estuarine in the Lutetian-Bartonian (Man Aike Formation). During the Rupelian, a continental environment with meandering rivers and overbank marshes was established (Río Leona Formation). This area was flooded in the early Burdigalian (Estancia 25 de Mayo Formation) during the Patagonian Transgression, but emerged again during the late Burdigalian (Santa Cruz Formation). Measured palaeocurrent directions in this Mesozoic-Cenozoic succession indicate source areas situated between the northeast and east-southeast during the Late Cretaceous, east-southeast during the middle Eocene, and southwest during the early Oligocene to early Miocene. This is confirmed by detrital zircon age populations in the different units, which can be linked to probable sources of similar ages in these areas. The east-southeastern provenance is here identified as the Antarctic Peninsula or its northeastern extension, which is postulated to have been attached to Fuegian Patagonia during the Eocene. The southwestern and western sources were exhumed during gradual uplift of the Southern Patagonian Andes, coinciding with a change from marine to continental conditions in the Magallanes-Austral Basin, as well as a decrease in mean annual temperature and precipitation indicated by fossil leaves in the Río Leona Formation. The rain shadow to the east of the Andes thus started to develop here during the late Eocene-early Oligocene (~ 34 Ma), long before the “Quechua Phase” of Andean tectonics (19–18 Ma) that is generally invoked for its evolution at lower latitudes.
The horizontal distribution and vertical structure of orographic rain are discussed. It is shown that orographic rain is difficult to measure by means of raingage networks or by radar. The observational evidence reviewed supports the widespread applicability of a conceptual model by Bergerson, according to which small droplets in a low level orographic 'feeder cloud' located mainly below the O C level are washed out by raindrops falling from a pre-existing 'seeder cloud'. -from STAR, 18(24), 1980
The western margin of southern South America bears cool temperate rainforest over a narrow landmass of some 17.5° of latitude, encompassing great physiographic diversity. The South American rainforest zone constitutes a remarkable forest island, widely separated from the closest wet, closed forest types on the South American continent by 1500 km to 2000 km. To the north, it is bound by seasonal, mediterranean-type climate scrublands and one of the driest deserts on earth, the Atacama. To the east, the rainforest intergrades with a narrow band of deciduous Nothofagus or Austrocedrus chilensis coniferous forest, followed by dry Patagonian steppe. Southward is the Antarctica continent, and westward the Pacific Ocean. In this forest island are found high productivity levels (Schmidt & Lara, 1985), the second-longest-living tree in the world—Fitzroya cupressoides attaining more than 3600 years (Lara, 1993), and many obligately outbred woody species (Riveros, 1991).
CORRESPONDENCE analysis of dicot leaf physiognomy of modern vegetational samples from a wide range of environments indicates that >70% of physiognomic variation corresponds to water or temperature factors, or both. Despite wide variation in single physiognomic characters, overall trends can be used to distinguish between samples from different climates. Some climate parameters are well correlated with changes in physiognomy, so that climate characteristics can be inferred from physiognomic analyses. Here I apply this climate-leaf analysis multivariate program (CLAMP) to leaf assemblages from the Cretaceous/Tertiary boundary. The results indicate a fourfold increase in precipitation at the boundary and an increase in mean annual temperature of 10°C. These levels persisted for 0.5-1.0 Myr, after which precipitation decreased to about three times the values for the latest Cretaceous, and the mean annual temperature decreased to 5-6°C above latest Cretaceous values.
PALAEOFLORISTIC ANALYSIS OF THE RIO GUILLERMO FORMATION (LATE EOCENE-EARLY OLIGOCENE?), SANTA CRUZ, ARGENTINA. Macrofloristic Paleogene units of southernmost Patagonia have few palaeobotanical studies. In this paper a new fossil leaf collection recovered from the Río Guillermo Formation (late Eocene—early Oligocene?) is analyzed. The palaeobotanical analysis reveals the presence of 10 fossil species, most of them related to Nothofagus Blume (Nothofagaceae), being the specimens of “Myrcia” bagualensis (Myrtaceae) the most abundant in the collection. Specimens referred to the families Rosaceae, Anacardiaceae, Lauraceae and Fagaceae were also recognized. The palaeofloristic assemblage from the Río Guillermo Formation is dominated by cold temperate taxa suggesting the presence of subantarctic paleofloras in this area. The great similarities between the Río Guillermo flora and that of the Oligocene Loreto Formation, coupled with the palaeoclimatic inferences, might indicate a younger age than previously suggested for the Río Guillermo Formation.
Paleogene, Maastrichtian, and Miocene floras are reviewed. They are located on continental margins, where several sedimentary basins developed. The affinities of the fossil genera to living ones allow the recognition of three paleofloras: Neotropical, Mixed, and Antarctic. These could be the forerunners, respectively, of the presently more humid dominions in Neotropical Region (Caribbean, Amazonic, and Guayano), of the drier ones (Chaqueno and Andino-Patagonico), and of the Subantarctic Dominion of the Antarctic Region. The South American climate, as indicated by the fossil floras, showed a trend to higher temperatures during the Paleocene and Lower Eocene, and a deterioration through the Middle and Upper Eocene.
To test multiple regression models developed to predict seven variables of climate from leaf margin and size characters, leaf character data were collected from modern woodland and rainforest plant communities in Uganda. These localities were chosen for their structural similarity to two fossil sites for which climate values were desired. The test indicated that for these communities, the model accurately predicts mean annual temperature. However, the multiple regression models overestimate seasonality of temperature and mean annual and seasonal precipitation amounts for the two modern communities. Reasons for the models' inaccuracies may include, no African analog in the non-African database on which the model is based, too much intraspecific variability in leaf size (an important character in precipitation models), and relationships between leaf form and climate that may not be well defined by multiple regression. Mean annual temperatures were reconstructed for two Miocene paleobotanical localities from the Tugen Hills of the eastern rift valley, Kenya, using leaf form data (primarily margin characters). The results indicate that mean annual temperatures at Kabarsero (12.6 Ma), and Kapturo (6.7–7.2 Ma), were essentially equivalent to temperatures at those localities today and differed little from one another. The Kapturo paleofloral assemblage is a deciduous woodland interpreted as indicating less available or more seasonal moisture than the Kabarsero paleofloral assemblage, a wet forest with West African floral affinities.Laser-fusion 40Ar39Ar dating of volcanic materials at Kapturo provides the first control of this paleoflora, bracketed by a 7.2 Ma trachyte at the base of the sedimentary sequence, and an age of 6.7 Ma on a reworked tuff overlying the fossiliferous horizon. The chronologic data places the paleofloral assemblage in stratigraphic context relative to other Tugen Hills units containing paleofloras and abundant vertebrate remains including hominoids.
"Measuring Biological Diversity assumes no specialist mathematical knowledge and includes worked examples and links to web-based software. It will be essential reading for all students, researchers, and managers who need to measure biological diversity."--BOOK JACKET.
Oceanic conditions around southern South America and the Antarctic Peninsula have a major influence on climate patterns in these subcontinents. During the Tertiary, changes in ocean water temperatures and currents also strongly affected the continental climates and seem to have been controlled in turn by global tectonic events and sea-level changes. During periods of accelerated sea-floor spreading, an increase in the mid-ocean ridge volumes and the outpouring of basaltic lavas caused a rise in sea-level and mean ocean temperature, accompanied by the large-scale release of CO2. The precursor of the South Equatorial Current would have crossed the East Pacific Rise twice before reaching the coast of southern South America, thus heating up considerably during periods of ridge activity. The absence of the Antarctic Circumpolar Current before the opening of the Drake Passage suggests that the current flowing north along the present western seaboard of southern South American could have been temperate even during periods of ridge inactivity, which might explain the generally warm temperatures recorded in the Southeast Pacific from the early Oligocene to middle Miocene. Along the east coast of southern South America, water temperatures also fluctuated between temperate-cool and warm until the early Miocene, when the first incursion of temperate-cold to cold Antarctic waters is recorded. The cold Falkland/Malvinas Current initiated only after the middle Miocene. After the opening of the Drake Passage, the South Equatorial Current would have joined the newly developed, cold Antarctic Circumpolar Current on its way to Southern South America. During periods of increased sea-floor spreading, it would have contributed heat to the Antarctic Circumpolar Current that caused a poleward shift in climatic belts. However, periods of decreased sea-floor spreading would have been accompanied by diminishing ridge volumes and older, cooler and denser oceanic plates, causing global sea-level falls. This would have resulted in a narrowing of the Drake Passage, an intensification of the Antarctic Circumpolar Current that enhanced the isolation of Antarctica from warmer northern waters, and increased glaciation on the Antarctic Peninsula. Colder ocean surface waters would also have trapped more CO2, enhancing climate cooling on the adjacent continents. During these periods the atmospheric belts shifted equatorward and increased the latitudinal thermal gradient, leading to higher wind velocities and enhanced oceanic upwelling along the western seaboard of Southern South America.
Fossil floras are an important source of quantitative terrestrial paleoclimate data. Many paleoclimate estimates are based on relationships observed in modern vegetation between leaf morphology and climate, such as the increase in the percentage of entire-margined species with increasing temperature and the increase in leaf size with increasing precipitation. An important question is whether these observed relationships are universal or regional; for example, recent stud- ies suggest that significant differences exist between floras from three domains: the Northern Hemi- sphere, New Zealand/Australia, and subalpine zones. Also, debate exists over which statistical models of modern data sets, univariate or multivariate, provide the most accurate estimates of pa- leoclimate. In this study, 12 foliage samples from living Bolivian forests are compared with data sets from different regions. Models based on data sets from North America and Japan, namely the Climate-Leaf Analysis Multivariate Program (CLAMP) data set of J. A. Wolfe, and from east Asia produce reasonably accurate estimates of temperature and precipitation, suggesting that the cli- mate-leaf morphology relationships for Bolivian vegetation do not differ significantly from those for Northern Hemisphere vegetation. The mean leaf size for a given mean annual precipitation is smaller than for a data set from the Western Hemisphere and Africa, but this difference is most likely due to different sampling methods. As for estimating climate from fossil floras, these results, along with the analysis of four other regional data sets, imply that the most accurate climate es- timates will be produced by the predictor data set with the most similar climate-leaf morphology relationships. Unfortunately, our present lack of understanding of why climate-morphology rela- tionships vary between the North America/Japan, New Zealand/Australia, and subalpine domains makes it difficult to identify data sets similar to paleofloras. Until we learn more, it is probably best to compare fossil floras to predictor data sets from the same domain. The performance of the var- ious statistical methods depends on the nature of the predictor data set. Multiple regression anal- ysis tends to produce the most accurate estimates for small data sets with a narrow range of en- vironmental variation that have similar relationships to the flora, and linear regression or canonical correspondence analysis for the larger and more varied CLAMP data set. If a similar predictor data set is not available, then nearest-neighbor analysis can still produce accurate paleoclimate esti- mates.