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PubMed2003

The evolution of body size in extant groups of North American freshwater fishes: speciation, size distributions, and Cope's rule.

Change in body size within an evolutionary lineage over time has been under investigation since the synthesis of Cope's rule, which suggested that there is a tendency for mammals to evolve larger body size. Data from the fossil record have subsequently been examined for several other taxonomic groups to determine whether they also displayed an evolutionary increase in body size. However, we are not aware of any species-level study that has investigated the evolution of body size within an extant continental group. Data acquired from the fossil record and data derived from the evolutionary relationships of extant species are not similar, with each set exhibiting both strengths and weaknesses related to inferring evolutionary patterns. Consequently, expectation that general trends exhibited in the fossil record will correspond to patterns in extant groups is not necessarily warranted. Using phylogenetic relationships of extant species, we show that five of nine families of North American freshwater fishes exhibit an evolutionary trend of decreasing body size. These trends result from the basal position of large species and the more derived position of small species within families. Such trends may be caused by the invasion of small streams and subsequent isolation and speciation. This pattern, potentially influenced by size-biased dispersal rates and the high percentage of small streams in North America, suggests a scenario that could result in the generation of the size-frequency distribution of North American freshwater fishes.

Animals↗

PubMed1997

Molecular systematics of the Canidae.

Despite numerous systematic studies, the relationships among many species within the dog family, Canidae, remain unresolved. Two problems of broad evolutionary significance are the origins of the taxonomically rich canidae fauna of South America and the development in three species of the trenchant heel, a unique meat-cutting blade on the lower first molar. The first problem is of interest because the fossil record provides little evidence for the origins of divergent South American species such as the maned wolf and the bush dog. The second issue is problematic because the trenchant heel, although complex in form, may have evolved independently to assist in the processing of meat. We attempted to resolve these two issues and five other specific taxonomic controversies by phylogenetic analysis of 2,001 base pairs of mitochondrial DNA (mtDNA) sequence data from 23 canidae species. The mtDNA tree topology, coupled with data from the fossil record, and estimates of rates of DNA sequence divergence suggest at least three and possibly four North American invasions of South America. This result implies that an important chapter in the evolution of modern canids remains to be discovered in the fossil record and that the South American canidae endemism is as much the result of extinction outside of South America as it is due to speciation within South America. The origin of the trenchant heel is not well resolved by our data, although the maximum parsimony tree is weakly consistent with a single origin followed by multiple losses of the character in several extant species. A combined analysis of the mtDNA data and published morphological data provides unexpected support for a monophyletic South American canidae clade. However, the homogeneity partition tests indicate significant heterogeneity between the two data sets.

Animals↗

PubMed2005

A Roman correspondence: George Ent and Cassiano dal Pozzo, 1637-55.

George Ent (FRS 1663), a distinguish physician, was in Rome in 1636, visited the notable collector Cassiano dal Pozzo and saw his Paper Museum. After he returned to London he carried on a correspondence with Cassiano in letters of more than ordinary interest. Cassiano had sent Ent specimens of fossil wood and a table made from fossil wood. They had come from the estates at Acquasparta belonging to Prince Federico Cesi, the founder of the Accademia dei Lincie. The specimens and the table were shown to early meetings of The Royal Society and had a significant part in the developing debate on the origin of fossils. The letters also record exchanges of books between London and Rome. Among medical matters there is news of William Harvey and his works.

Correspondence as Topic↗

PubMed2001

Evolution of the angiosperms: calibrating the family tree.

Growing evidence of morphological diversity in angiosperm flowers, seeds and pollen from the mid Cretaceous and the presence of derived lineages from increasingly older geological deposits both imply that the timing of early angiosperm cladogenesis is older than fossil-based estimates have indicated. An alternative to fossils for calibrating the phylogeny comes from divergence in DNA sequence data. Here, angiosperm divergence times are estimated using non-parametric rate smoothing and a three-gene dataset covering ca. 75% of all angiosperm families recognized in recent classifications. The results provide an initial hypothesis of angiosperm diversification times. Using an internal calibration point, an independent evaluation of angiosperm and eudicot origins is performed. The origin of the crown group of extant angiosperms is indicated to be Early to Middle Jurassic (179-158 Myr), and the origin of eudicots is resolved as Late Jurassic to mid Cretaceous (147-131 Myr). Both estimates, despite a conservative calibration point, are older than current fossil-based estimates.

Calibration↗

PubMed2004

Studying the effect of environmental change on biotic evolution: past genetic contributions, current work and future directions.

Evolutionary geneticists currently face a major scientific opportunity when integrating across the rapidly increasing amount of genetic data and existing biological scenarios based on ecology, fossils or climate models. Although genetic data acquisition and analysis have improved tremendously, several limitations remain. Here, we discuss the feedback between history and genetic variation in the face of environmental change with increasing taxonomic and temporal scale, as well as the major challenges that lie ahead. In particular, we focus on recent developments in two promising genetic methods, those of 'phylochronology' and 'molecular clocks'. With the advent of ancient DNA techniques, we can now directly sample the recent past. We illustrate this amazing and largely untapped utility of ancient DNA extracted from accurately dated localities with documented environmental changes. Innovative statistical analyses of these genetic data expose the direct effect of recent environmental change on genetic endurance, or maintenance of genetic variation. The 'molecular clock' (assumption of a linear relationship between genetic distance and evolutionary time) has been used extensively in phylogenetic studies to infer time and correlation between lineage divergence time and concurrent environmental change. Several studies at both population and species scale support a persuasive relationship between particular perturbation events and time of biotic divergence. However, we are still a way from gleaning an overall pattern to this relationship, which is a prerequisite to ultimately understanding the mechanisms by which past environments have shaped the evolutionary trajectory. Current obstacles include as-yet undecided reasons behind the frequent discrepancy between molecular and fossil time estimates, and the frequent lack of consideration of extensive confidence intervals around time estimates. We suggest that use and interpretation of both ancient DNA and molecular clocks is most effective when results are synthesized with palaeontological (fossil) and ecological (life history) information.

Animals↗

PubMed2006

Quantitative analysis of dental microwear in threespine stickleback: a new approach to analysis of trophic ecology in aquatic vertebrates.

1. The threespine stickleback Gasterosteus aculeatus is an important model organism in studies of genomic and phenotypic evolution, adaptation and speciation. Fossil Gasterosteus offer the potential to test models derived from studies of extant fishes over true evolutionary time-scales. Competition for food resources, for example, plays an important part in stickleback speciation, causing divergence in food gathering traits and ecological character displacement, but it is not possible to test this model in fossils because evidence of diet is almost never preserved. 2. We demonstrate here that quantitative analysis of dental microwear, a technique previously applied only to mammals, provides a reliable guide to the dietary preferences of stickleback. Teeth from stickleback raised under laboratory conditions exhibit microwear patterns that vary systematically according to substrate coarseness and whether fishes feed on Daphnia within the water column, or on chironomid larvae from the bottom. Furthermore, microwear data exhibit a progressive shift in their distribution that tracks differences in experimental feeding treatments. 3. Microwear in wild populations also exhibits a relationship with feeding. In blind assessments of trophic niche based on microwear patterns we were able to correctly assign all but one equivocal population to trophic group. Microwear data from wild stickleback exhibit a shift in distribution comparable with that observed across the range of treatments in the laboratory and these allow populations to be ranked according to the degree to which they approach fully benthic or fully limnetic feeding. 4. Our results demonstrate that microwear has the potential to be a powerful tool in the analysis of fish trophic ecology, particularly in the analysis of species pairs and niche differentiation. It has advantages over the trophic snapshot provided by analysis of stomach contents in that microwear reflects feeding and food preferences over a longer period of time, and can be applied where these data are unavailable. Furthermore, it is applicable to extinct organisms and fossils, allowing the role of trophic ecology, niche partitioning and competition over evolutionary time-scales to be investigated for the first time.

Animals↗

PubMed1976

Affinites of tertiary hominoid femora.

Uni- and multivariate analyses of 244 extant and 4 fossil primate femora indicate that none of the Tertiary hominoid fossil femora resembles the great apes. The dryopithecine femur from Moboko, Kenya, is most like Nasalis. Pliopithecus and the fossil from Eppelsheim are similar to one another and to Hylobates, but unlike the African dryopithecine. A new specimen from the Miocene deposits of Songhor, Kenya, is very similar to Hylobates and is probably a member of the hylobatine taxon, Lomnopithecus macinnesi. The lack of similarity between the African dryopithecine femur and the femora of the extant great apes in further evidence that the typical hominoid postcranial morphology evolved after the middle Miocene period.

Animals↗

PubMed2005

Late Quaternary loss of genetic diversity in muskox (Ovibos).

BACKGROUND: The modern wildherd of the tundra muskox (Ovibos moschatus) is native only to the New World (northern North America and Greenland), and its genetic diversity is notably low. However, like several other megafaunal mammals, muskoxen enjoyed a holarctic distribution during the late Pleistocene. To investigate whether collapse in range and loss of diversity might be correlated, we collected mitochondrial sequence data (hypervariable region and cytochrome b) from muskox fossil material recovered from localities in northeastern Asia and the Arctic Archipelago of northern North America, dating from late Pleistocene to late Holocene, and compared our results to existing databases for modern muskoxen. RESULTS: Two classes of haplotypes were detected in the fossil material. "Surviving haplotypes" (SHs), closely similar or identical to haplotypes found in modern muskoxen and ranging in age from approximately 22,000 to approximately 160 yrbp, were found in all New World samples as well as some samples from northeastern Asia. "Extinct haplotypes" (EHs), dating between approximately 44,000 and ~18,000 yrbp, were found only in material from the Taimyr Peninsula and New Siberian Islands in northeastern Asia. EHs were not found in the Holocene muskoxen specimens available for this study, nor have they been found in other studies of extant muskox populations. CONCLUSION: We provisionally interpret this evidence as showing that genetic variability was reduced in muskoxen after the Last Glacial Maximum but before the mid-Holocene, or roughly within the interval 18,000-4,000 yrbp. Narrowing this gap further will require the recovery of more fossils and additional genetic information from this interval.

Animals↗

PubMed1979

Atmospheric CO2 consequences of heavy dependence on coal.

Accurate and regular measurements of the concentration of CO2 in the atmosphere during the past 20 years show an accelerating increase. Although clearing of tropical forests has released large amounts of carbon to the atmosphere, evidence is strong that a major contributor is the combustion of fossil fuels. Future energy demands of the world will require extensive further exploitation of fossil fuels, and projections show that without major development of nonfossil fuel alternatives, the atmospheric concentration will double within the next 75 years. Four issues require serious attention. The developing countries will require vastly increased amounts of energy. Major efforts to develop suitable (inexpensive) nonfossil energy sources to meet at least a portion of this demand are required. The distribution of carbon released from fossil fuels and from other anthropogenic sources among the reservoirs of the carbon cycle must be better defined. Uncertainties regarding the effect of the increased concentration of CO2 in the atmosphere on global climate must be reduced. Possible political and social responses to a substantial climate change must be studied in order to more fully understand all of the implication of increased atmospheric CO2.

Air Pollution↗

PubMed1983

Community and occupational studies of lung cancer and polycyclic organic matter.

Finland is used as a model in attempts to study the possible association of the incidence of lung cancer and exposure of population to fossil fuel combustion products. Unfortunately because of great geographical variation of unknown origin in the incidence of lung cancer in Finland, detailed studies of the possible role of an individual exposure in the lung cancer risk are not possible. This background variation in the incidence is much greater than variation carried by any known etiological factor and does not clearly correlate with the degree of urbanization, industrialization, regional use of fossil fuels, number of motor vehicles or smoking habits. To get more precise information on the possible association of lung cancer incidence with exposure to fossil fuel combustion products, occupational studies serve as powerful tools. The definition of population is more reliable and the measurement of exposures can be done more precisely; moreover the management of confounding and modifying factors is more effective than in community studies. So far the studies carried out among the Finnish working population exposed to PAH compounds reveal an association between the lung cancer risk and exposure to PAHs.

Adult↗

PubMed2001

Virtual anthropology: the digital evolution in anthropological sciences.

The discovery and explanation of differences among organisms is a major concern for evolutionary and systematic biologists. In physical anthropology, the discrimination of taxa and the qualitative and quantitative description of ontogenetic or evolutionary change require, of course, the analysis of morphological features. Since the 1960s, a remarkable amount of fossil material was excavated, some of it still awaiting a detailed first analysis, some of it requiring re-examination by more developed methods. While the fossil record grew continuously, a revolution in anthropological research took place with advances in computer technology in the 1980s: a handful of innovative researchers working in specialized anthropology laboratories or medical departments developed the methodological inventory needed to extract critical information from subjects in vivo and from fossilized remains. A considerable part of this information is preserved in the physically heretofore inaccessible interior of anatomical structures. Virtual Anthropology (VA) is a means of making them visible and measurable. Thus, VA also allows access to 'hidden' landmarks; in addition, the large number of semilandmarks accessible on the form enhances the power of Geometric Morphometrics analysis. Furthermore, the density information in volume data allows manipulations such as segmentation, impossible with the real, physical object. Moreover, metric body measurements generally, and cranial measurements specifically, are also an important source of information for the analysis of the ontogenetic development of the skeletal system, and--last but not least--for clinical use (e.g., operation planning, operation simulation, prosthetics). Thus, there developed a fruitful interdisciplinary cooperation between statistics, medicine, and physical anthropology.

Anthropology, Physical↗

PubMed2001

Habitat-related error in estimating temperatures from leaf margins in a humid tropical forest.

Leaf margin characters are strong predictors of mean annual temperature (MAT) in modern plant communities and widely used tools for reconstructing paleoclimates from fossil floras. However, the frequency of nonentire-margined species may vary dramatically between different habitats of the same forest. In this paper we explore the potential for this habitat variation to introduce error into temperature reconstructions, based on field data from a modern lowland forest in Amazonian Ecuador.The data show that the provenance of leaves can influence temperature estimates to an important degree and in a consistent direction. Woody plants growing along lakes and rivers underestimated MAT by 2.5°-5°C, while those in closed-canopy forest provided very accurate predictions. The high proportion of liana species with toothed leaves in lakeside and riverside samples appears to be responsible for a large part of the bias. Samples from closed-canopy forest that included both lianas and trees, however, were more accurate than tree-only or liana-only samples.We conclude that paleotemperature reconstructions based on leaf margin characters will be misleading to the extent that fossilization provides a better record of certain habitats than others. The preponderance of lake and river deposits in the angiosperm fossil record suggests that underestimation of mean annual paleotemperature may be common.

Journal Article↗

PubMed2001

Compound pollen cone in a Paleozoic conifer.

A rich fossil biota from a Pennsylvanian age deposit of eastern North America contains numerous vegetative and fertile specimens that conform to a single species of primitive walchian conifers. Among the specimens is a compound pollen cone that comprises closely spaced, helically arranged, leaf-like bracts with axillary dwarf shoots. The specimen looks superficially similar to an ultimate vegetative conifer shoot, but there are small appendages in the axil of each bract that represent the fertile dwarf shoots. Dwarf shoots consist of an axis that bears sterile scales and sporophylls with erect pollen sacs. Pollen found in the sacs is monosaccate and conforms to the sporae dispersae genus Potonieisporites Bhardwaj. This cone is a compound shoot system that is morphologically equivalent to the ovulate cones of conifers and to the pollen cones of Paleozoic cordaitaleans and modern gnetophytes. Therefore, it is fundamentally different from the simple pollen cones of other fossil and modern conifers. Discovery of this specimen unexpectedly supports molecular studies that predict a close relationship between Coniferales and Gnetales, and provides fossil evidence to help reconcile the discordant phylogenetic hypotheses of seed plant systematics that have been developed from morphological and molecular data.

Journal Article↗

PubMed2001

Dipteronia (Sapindaceae) from the Tertiary of North America and implications for the phytogeographic history of the Aceroideae.

The fossil record of Dipteronia, the sister genus of Acer, is reviewed based on diagnostic winged fruits from the Tertiary of western North America. Today the genus is endemic to eastern Asia with two extant species in central and southern China, but it is well represented in the Tertiary of western North America, ranging from the Paleocene to the Oligocene with the greatest number of occurrences in the middle to late Eocene. There are no known fossil occurrences outside of North America. The fossil fruits, assigned to the new species D. brownii sp. nov., are smaller than those of both living species and were tricarpellate as well as bicarpellate in contrast to the modern species, which are almost exclusively bicarpellate. The tricarpellate condition may be plesiomorphic for Dipteronia and perhaps Aceroideae. The area of origin for Dipteronia is unknown, but it seems likely to have been either Asia or North America, with the genus crossing Beringia in the Paleogene.

Journal Article↗

PubMed2004

Biogeochemical features of lipids in endolithic microbial communities in the Ross Desert (McMurdo Dry Valleys), Antarctica.

Endolithic microbial communities inhabiting porous rocks in the cold, dry mountainous regions of Antarctica have been studied extensively as examples of life's adaptations to extreme environments. Here, we examine hydrocarbons and fatty acids occurring in these communities in order to clarify their biogeochemical features with respect to source organisms, microbial activity, fossilization processes and the influence of Gondwanaland sediments. Unusually, long-chain (>C19) n-alkanes and anteiso-alkanes were often the major hydrocarbons in the samples. A suite of n-alkanoic acids (n-C9-n-C32) and long-chain anteiso-alkanoic acids (a-C20-a-C30) were found, along with short-chain iso- and anteiso-alkanoic acids, and n-alkenoic acids. The relationship between long-chain n-alkanoic acids (n-C20-n-C32) and long-chain anteiso-alkanoic acids suggests that these compounds probably originated from the same group of microorganisms, such as bacteria or endolithic lichens, under moderate pH conditions (pH 3-5). Relatively high trans/cis-C16:1 alkenoic acid ratios suggest the presence of unfavorable environmental conditions in the endolithic microbial habitat. Normal-alkenoic/alkanoic acid ratios may be a useful marker for the fossilization of endolithic microbial communities. Thermally matured triterpanes and steranes from fossilized associations on Mount Fleming strongly suggest the presence of Gondwanaland sediments formed during Devonian and Jurassic (400-180 million years ago).

Alkanes↗

PubMedDate not supplied

Preliminary study on the age of Yuanmou man by palaeomagnetic technique.

Since the discovery of the fossil teeth of Yuanmou man (Homo erectus yuanmouensis) on May 1, 1965 from Yuanmou county, Yunnan Province, the Institute of Geomechanics, relying on the local poor and lower-middle peasants and co-operating with other units concerned, has been conducting intensive researches on the fossil man-bearing strata as well as Quaternary glaciation. Palaeomagnetic technique lately used in the study has for the first time shown that the Yuanmou man appeared around 1.7 million years ago, earlier than both Peking man and Lantien man. Hence the age formerly assigned to the earliest fossil man in China has to be increased by more than a million years. Furthermore, as the age of Yuanmou formation is fixed at 1.5--3.1 million years, the length of Quaternary has to be extended by more than two million years. Of special interest is that under the Yuanmou formation there occur glacial traces which prove beyond doubt the existence of glaciation over 3 million years ago. This is a new discovery in the Quaternary history of China, and provides a new approach to the future study of this period.

China↗

PubMed1978

The energy cost of overweight in the United States.

We have calculated the total fossil energy equivalent of the food calories saved by reducing the present degree of overweight (2.3 billion pounds for the adult United States population) to optimum body weight and the annual fossil energy reduction once all Americans reached their optimum weight. The energy saved by dieting to reach optimal weight is equivalent to 1.3 billion gallons of gasoline and the annual energy savings would more than supply the annual residential electrical demands of Boston, Chicago, San Francisco, and Washington, DC.

Adolescent↗

PubMed1996

Brief communication: new primate remains from the Miocene of Namibia, southern Africa.

Miocene primates from southern Africa are extremely rare. For this reason we wish to place on record several interesting new fossil primate specimens recently recovered from the Miocene sites of Berg Aukas and Harasib in the Otavi Mountain region of northern Namibia. The new finds consist of a virtually complete atlas vertebra from Berg Aukas attributable to the hominoid Otavipithecus namibiensis and two teeth and four postcranial fragments from Harasib referrable to Cercopithecoidea. The atlas vertebra exhibits anatomical characteristics intermediate between those of modern cercopithecoids and hominoids which may be indicative of a transition from pronograde to orthograde postures. The cercopithecoid remains show that the earliest Old World monkeys known from southern Africa were small, approximately the size of vervet monkeys. These new specimens are important because they provide the first evidence relating to possible positional behaviors of Otavipithecus and the earliest fossil record of cercopithecoids from southern Africa.

Animals↗