Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PALEOBIOLOGY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed2004

Short-wave infrared reflectance investigation of sites of paleobiological interest: applications for Mars exploration.

Rover missions to the rocky bodies of the Solar System and especially to Mars require lightweight, portable instruments that use minimal power, require no sample preparation, and provide suitably diagnostic mineralogical information to an Earth-based exploration team. Short-wave infrared (SWIR) spectroscopic instruments such as the Portable Infrared Mineral Analyser (PIMA, Integrated Spectronics Pty Ltd., Baulkham Hills, NSW, Australia) fulfill all these requirements. We describe an investigation of a possible Mars analogue site using a PIMA instrument. A survey was carried out on the Strelley Pool Chert, an outcrop of stromatolitic, silicified Archean carbonate and clastic succession in the Pilbara Craton, interpreted as being modified by hydrothermal processes. The results of this study demonstrate the capability of SWIR techniques to add significantly to the geological interpretation of such hydrothermally altered outcrops. Minerals identified include dolomite, white micas such as illite-muscovite, and chlorite. In addition, the detection of pyrophyllite in a bleached and altered unit directly beneath the succession suggests acidic, sulfur-rich hydrothermal activity may have interacted with the silicified sediments of the Strelley Pool Chert.

Australia↗
PubMed2000

The evolutionary physiology of animal flight: paleobiological and present perspectives.

Recent geophysical analyses suggest the presence of a late Paleozoic oxygen pulse beginning in the late Devonian and continuing through to the late Carboniferous. During this period, plant terrestrialization and global carbon deposition resulted in a dramatic increase in atmospheric oxygen levels, ultimately yielding concentrations potentially as high as 35% relative to the contemporary value of 21%. Such hyperoxia of the late Paleozoic atmosphere may have physiologically facilitated the initial evolution of insect flight metabolism. Widespread gigantism in late Paleozoic insects and other arthropods is also consistent with enhanced oxygen flux within diffusion-limited tracheal systems. Because total atmospheric pressure increases with increased oxygen partial pressure, concurrently hyperdense conditions would have augmented aerodynamic force production in early forms of flying insects. By the late Permian, evolution of decompositional microbial and fungal communities, together with disequilibrium in rates of carbon deposition, gradually reduced oxygen concentrations to values possibly as low as 15%. The disappearance of giant insects by the end of the Permian is consistent with extinction of these taxa for reasons of asphyxiation on a geological time scale. As with winged insects, the multiple historical origins of vertebrate flight in the late Jurassic and Cretaceous correlate temporally with periods of elevated atmospheric oxygen. Much discussion of flight performance in Archaeopteryx assumes a contemporary atmospheric composition. Elevated oxygen levels in the mid- to late Mesozoic would, however, have facilitated aerodynamic force production and enhanced muscle power output for ancestral birds, as well as for precursors to bats and pterosaurs.

Animals↗
PubMed1996

Paleobiology, community ecology, and scales of ecological pattern.

The fossil record provides a wealth of data on the role of regional processes and historical events in shaping biological communities over a variety of time scales. The Quaternary record with its evidence of repeated climatic change shows that both terrestrial and marine species shifted independently rather than as cohesive assemblages over scales of thousands of years. Larger scale patterns also show a strong individualistic component to taxon dynamics; assemblage stability, when it occurs, is difficult to separate from shared responses to low rates of environmental change. Nevertheless, the fossil record does suggest that some biotic interactions influence large-scale ecological and evolutionary patterns, albeit in more diffuse and protracted fashions than those generally studied by community ecologists. These include: (1) the resistance by incumbents to the establishment of new or invading taxa, with episodes of explosive diversification often appearing contingent on the removal of incumbents at extinction events; (2) steady states of within-habitat and global diversity at longer time scales (10(7)-l0(8) yr), despite enormous turnover of taxa; and (3) morphological and biogeographic responses to increased intensities of predation and substratum disturbance over similarly long time scales. The behavior of species and communities over the array of temporal and spatial scales in the fossil record takes on additional significance for framing conservation strategies, and for understanding recovery of species, lineages, and communities from environmental changes.

Animals↗
PubMed1995

Paleobiology of the Mesoproterozoic Billyakh Group, Anabar Uplift, northern Siberia.

Silicified peritidal carbonates of the Mesoproterozoic Kotuikan and Yusmastakh Formations, Anabar Uplift, northeastern Siberia, contain exceptionally well-preserved microfossils. The assemblage is dominated by ellipsoidal akinetes of nostocalean cyanobacteria (Archaeoellipsoides) and problematic spheroidal unicells (Myxococcoides); both are allochthonous and presumably planktonic. The assemblage also includes distinctive mat-forming scytonematacean and entophysalidacean cyanobacteria, diverse short trichomes interpreted as cyanobacterial hormogonia or germinated akinetes, rare longer trichomes, and several types of colonial unicells. Although many taxa in the Kotuikan-Yusmastakh assemblage are long-ranging prokaryotes, the overall character of the assemblage is distinctly Mesoproterozoic, with its major features shared by broadly coeval floras from Canada, China, India, and elsewhere in Siberia. Microfossils also occur in middle to inner shelf shales of the Ust'-Il'ya and lower Kotuikan Formations. Leiosphaerid acritarchs (up to several hundred microns in diameter) characterize this facies. As in other Mesoproterozoic acritarch assemblages, acanthomorphic and other complex forms that typify Neoproterozoic assemblages are absent. The combination in Billyakh assemblages of exceptional preservation and low eukaryotic diversity supports the hypothesis that nucleated organisms diversified markedly near the Mesoproterozoic-Neoproterozoic boundary. The assemblages also demonstrate the antiquity of cyanobacteria capable of cell differentiation and suggest the importance of both changing peritidal substrates and evolving eukaryotes in determining stratigraphic patterns of Proterozoic prokaryotes. The permineralized assemblage contains 33 species belonging to 17 genera. Ten new species or new combinations are proposed: Archaeoellipsoides costatus n. sp., A. elongatus n. comb., A. dolichos n. comb., A. minor n. nom., A. crassus n. comb., A. major n. comb., A. bactroformis n. sp., Veteronostocale medium n. sp., Filiconstrictosus cephalon n. sp., and Partitiofilum yakschinii n. sp.

Bacteria↗
PubMed1987

Paleobiology of distinctive benthic microfossils from the upper Proterozoic Limestone-Dolomite "Series," central East Greenland.

Populations of Polybessurus bipartitus Fairchild ex Green et al., a large morphologically distinctive microfossil, occur in silicified carbonates of the Upper Proterozoic (700-800 Ma) Limestone-Dolomite "Series," central East Greenland. Large populations of well-preserved individuals permit reconstruction of P. bipartitus as a coccoidal unicell that "jetted" upward from the sediment by the highly unidirectional secretion of extracellular mucopolysaccharide envelopes. Reproduction by baeocyte formation is inferred on the basis of clustered envelope stalks produced by small cells. Sedimentological evidence indicates that P. bipartitus formed surficial crusts locally within a shallow peritidal carbonate platform. Among living microorganisms a close morphological, reproductive, and behavioral counterpart to Polybessurus is provided by populations of an as yet underscribed cyanobacterium found in coastal Bahamian environments similar to those in which the Proterozoic fossils occur. In general morphology and "jetting" behavior, this population resembles species of the genus Cyanostylon, Geitler (1925), but reproduces via baeocyte formation. Polybessurus is but one of the more than two dozen taxa in the richly fossiliferous biota of the Limestone-Dolomite "Series." This distinctive population, along with co-occurring filamentous cyanobacteria and other microfossils, contributes to an increasingly refined picture of ecological heterogeneity in late Proterozoic oceans.

Calcium Carbonate↗
PubMed1992

Peopling of the Americas: paleobiological evidence.

A subjective and bivariate analysis of 8500-10,000-year-old human fossil remains from North America substantiates that the fossils' closest affinities are with Asian populations. Within North American prehistoric Indian populations, increasing brachycephalization and the possible development of a larger, broader face are two structural trends that can be identified. In those respects where Paleo-Indian specimens differ from modern northern Asians and North American Indians, they tend to resemble southern Asian and European populations. These assessments generally support the inference that populations entered the New World relatively recently but before the modern northern Asian and North American features were fully developed. Based on the data examined, no date can be specified for time of entrance of the first populations, nor can the number of founding populations be discerned.

Anthropology, Physical↗
PubMed1995

Reverse transcriptase: mediator of genomic plasticity.

Reverse transcription has been an important mediator of genomic change. This influence dates back more than three billion years, when the RNA genome was converted into the DNA genome. While the current cellular role(s) of reverse transcriptase are not yet completely understood, it has become clear over the last few years that this enzyme is still responsible for generating significant genomic change and that its activities are one of the driving forces of evolution. Reverse transcriptase generates, for example, extra gene copies (retrogenes), using as a template mature messenger RNAs. Such retrogenes do not always end up as nonfunctional pseudogenes but form, after reinsertion into the genome, new unions with resident promoter elements that may alter the gene's temporal and/or spatial expression levels. More frequently, reverse transcriptase produces copies of nonmessenger RNAs, such as small nuclear or cytoplasmic RNAs. Extremely high copy numbers can be generated by this process. The resulting reinserted DNA copies are therefore referred to as short interspersed repetitive elements (SINEs). SINEs have long been considered selfish DNA, littering the genome via exponential propagation but not contributing to the host's fitness. Many SINEs, however, can give rise to novel genes encoding small RNAs, and are the migrant carriers of numerous control elements and sequence motifs that can equip resident genes with novel regulatory elements [Brosius J. and Gould S.J., Proc Natl Acad Sci USA 89, 10706-10710, 1992]. Retrosequences, such as SINEs and portions of retroelements (e.g., long terminal repeats, LTRs), are capable of donating sequence motifs for nucleosome positioning, DNA methylation, transcriptional enhancers and silencers, poly(A) addition sequences, determinants of RNA stability or transport, splice sites, and even amino acid codons for incorporation into open reading frames as novel protein domains. Retroposition can therefore be considered as a major pacemaker for evolution (including speciation). Retroposons, with their unique properties and actions, form the molecular basis of important evolutionary concepts, such as exaptation [Gould S.J. and Vrba E., Paleobiology 8, 4-15, 1982] and punctuated equilibrium [Elredge N. and Gould S.J. in Schopf T.J.M. (ed). Models in Paleobiology. Freeman, Cooper, San Francisco, 1972, pp. 82-115].

Animals↗
PubMed2005

Stable isotopes (delta13C and delta15N) of organic matrix from coral skeleton.

The evolutionary success of reef-building corals in nutrient-poor tropical waters is attributed to endosymbiotic dinoflagellates. The algae release photosynthetic products to the coral animal cells, augment nutrient flux, and enhance the rate of coral calcification. Natural abundance of stable isotopes (delta13C and delta18O) provides answers to modern and paleobiological questions about the effect of photosymbiosis on sources of carbon and oxygen in coral skeletal calcium carbonate. Here we compare 17 species of symbiotic and nonsymbiotic corals to determine whether evidence for photosymbiosis appears in stable isotopes (delta13C and delta15N) of an organic skeletal compartment, the coral skeletal organic matrix (OM). Mean OM delta13C in symbiotic and nonsymbiotic corals was similar (-26.08 per thousand vs. -24.31 per thousand), but mean OM delta15N was significantly depleted in 15N in the former (4.09 per thousand) relative to the latter (12.28 per thousand), indicating an effect of the algae on OM synthesis and revealing OM delta15N as a proxy for photosymbiosis. To answer an important paleobiological question about the origin of photosymbiosis in reef-building corals, we applied this proxy test to a fossil coral (Pachythecalis major) from the Triassic (240 million years ago) in which OM is preserved. Mean OM delta15N was 4.66 per thousand, suggesting that P. major was photosymbiotic. The results show that symbiotic algae augment coral calcification by contributing to the synthesis of skeletal OM and that they may have done so as early as the Triassic.

Animals↗
PubMed2005

Geologic constraints on the macroevolutionary history of marine animals.

The causes of mass extinctions and the nature of taxonomic radiations are central questions in paleobiology. Several episodes of taxonomic turnover in the fossil record, particularly the major mass extinctions, are generally thought to transcend known biases in the geologic record and are widely interpreted as distinct macroevolutionary phenomena that require unique forcing mechanisms. Here, by using a previously undescribed compilation of the durations of sedimentary rock sequences, I compare the rates of expansion and truncation of preserved marine sedimentary basins to rates of origination and extinction among Phanerozoic marine animal genera. Many features of the highly variable record of taxonomic first and last occurrences in the marine animal fossil record, including the major mass extinctions, the frequency distribution of genus longevities, and short- and long-term patterns of genus diversity, can be predicted on the basis of the temporal continuity and quantity of preserved sedimentary rock. Although these results suggest that geologically mediated sampling biases have distorted macroevolutionary patterns in the fossil record, preservation biases alone cannot easily explain the extent to which the sedimentary record duplicates paleobiological patterns. Instead, these results suggest that the processes responsible for producing variability in the sedimentary rock record, such as plate tectonics and sea-level change, may have been dominant and consistent macroevolutionary forces throughout the Phanerozoic.

Animals↗
PubMed1996

Dental microwear and microstructure in early oligocene primates from the Fayum, Egypt: implications for diet.

Textbook descriptions usually portray the Fayum anthropoideans as frugivores, with Parapithecus grangeri including a folivorous component in its diet and Apidium a component of hard-object feeding. Recent work with modern mammals has shown that analyses of both dental microwear and dental microstructure may yield insights into diet and tooth use. The purpose of this study was to combine these two techniques to gain a better perspective on the paleobiology of the Fayum higher primates. Dental microwear analyses involved the use of high resolution epoxy casts of Aegyptopithecus, Parapithecus, and Apidium housed in the Duke University Primate Center. Scanning electron micrographs were taken at x500, and all microwear features in each micrograph were digitized. For microstructure analyses, molar teeth were sectioned in a variety of planes, lightly etched, and photographed in the SEM. Results of the dental microwear analyses indicate that the three Fayum anthropoideans all clustered with modern primate frugivores but that there were also significant differences between Aegyptopithecus and the other two Fayum genera. By contrast, dental microstructure analyses showed important differences between Apidium and the other two genera. The reason for these differences probably lies in a combination of body size and dietary differences, with Aegyptopithecus occasionally feeding on hard objects and Apidium maximizing wear resistance through a unique emphasis of radial (rather than decussating) enamel.

Animals↗
PubMed1999

Incisor microwear, diet, and tooth use in three Amerindian populations.

Incisor microwear patterns have been shown to reflect aspects of diet and ingestive behaviors in a wide range of nonhuman primates. While some studies have suggested that anterior dental microwear might be used to infer unusual front tooth use practices in archaeological populations, quantitative work on modern human incisors has thus far been limited. In this study we examined dental microwear on the maxillary central incisors of three groups of humans: Aleutian Islanders (n = 16), Arikara from the Mobridge Site in South Dakota (n = 15), and a Late Woodland Bluff sample from Jersey County, Illinois (n = 17). High-resolution replicas were prepared and examined by scanning electron microscopy following conventional procedures. Photomicrographs were taken at consistent locations on the labial surface, and microwear was quantified using Microware 3.0 (Ungar, 1997). Statistical test results revealed significant differences among the groups in microwear feature densities, sizes, and shapes. The Aleut, Arikara, and Illinois Bluff samples showed a gradient of increasing microwear density, increasing linearity in feature shape, and decreasing feature size. These differences evidently correspond to amount of meat consumption, and apparently to degree of use of the incisors in heavy loading. No differences were observed between groups in heterogeneity of feature orientations, and no sex-related differences were found. Associations between incisor microwear on the one hand and subsistence practice and anterior tooth use on the other likely have important implications for the study of hominid paleobiology.

Fossils↗
PubMed2002

Ontogenetic study of the skull in modern humans and the common chimpanzees: neotenic hypothesis reconsidered with a tridimensional Procrustes analysis.

Heterochronic studies compare ontogenetic trajectories of an organ in different species: here, the skulls of common chimpanzees and modern humans. A growth trajectory requires three parameters: size, shape, and ontogenetic age. One of the great advantages of the Procrustes method is the precise definition of size and shape for whole organs such as the skull. The estimated ontogenetic age (dental stages) is added to the plot to give a graphical representation to compare growth trajectories. We used the skulls of 41 Homo sapiens and 50 Pan troglodytes at various stages of growth. The Procrustes superimposition of all specimens was completed by statistical procedures (principal component analysis, multivariate regression, and discriminant function) to calculate separately size-related shape changes (allometry common to chimpanzees and humans), and interspecific shape differences (discriminant function). The results confirm the neotenic theory of the human skull (sensu Gould [1977] Ontogeny and Phylogeny, Cambridge: Harvard University Press; Alberch et al. [1979] Paleobiology 5:296-317), but modify it slightly. Human growth is clearly retarded in terms of both the magnitude of changes (size-shape covariation) and shape alone (size-shape dissociation) with respect to the chimpanzees. At the end of growth, the adult skull in humans reaches an allometric shape (size-related shape) which is equivalent to that of juvenile chimpanzees with no permanent teeth, and a size which is equivalent to that of adult chimpanzees. Our results show that human neoteny involves not only shape retardation (paedomorphosis), but also changes in relative growth velocity. Before the eruption of the first molar, human growth is accelerated, and then strongly decelerated, relative to the growth of the chimpanzee as a reference. This entails a complex process, which explains why these species reach the same overall (i.e., brain + face) size in adult stage. The neotenic traits seem to concern primarily the function of encephalization, but less so other parts of the skull. Our results, based on the discriminant function, reveal that additional structural traits (corresponding to the nonallometric part of the shape which is specific to humans) are rather situated in the other part of the skull. They mainly concern the equilibrium of the head related to bipedalism, and the respiratory and masticatory functions. Thus, the reduced prognathism, the flexed cranial base (forward position of the foramen magnum which is brought closer to the palate), the reduced anterior portion of the face, the reduced glabella, and the prominent nose mainly correspond to functional innovations which have nothing to do with a neotenic process in human evolution. The statistical analysis used here gives us the possibility to point out that some traits, which have been classically described as paedomorphic because they superficially resemble juvenile traits, are in reality independent of growth.

Animals↗