SEARCH · PubMed Health

Results for “FOSSILS”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 127 records · Page 7Linked to original sources

PubMed2000

New fossil materials of the earliest new world monkey, Branisella boliviana, and the problem of platyrrhine origins.

Branisella boliviana, from the Late Oligocene of Salla, Bolivia, is the oldest fossil platyrrhine monkey discovered. To date, several fossil specimens of Branisella have been obtained, but most of them are fragmentary dentitions, so the animals craniodental morphology is still obscure. During the 1996 field season a pair of upper and lower jaw fragments and another nearly complete mandible were recovered. These new fossil materials reveal the following morphological features in Branisella: 1) P(2) is much smaller than P(3,4), whereas P(2) is relatively small but probably sexually dimorphic; 2) the zygomatic arch protrudes smoothly posterolaterally from the maxillary bone, as in extant Callicebus; 3) the mandibular arcade is nearly V-shaped and the symphysial angle, which is formed by the horizontal plane and the anterior face of mandibular symphysis, is about 40 degrees, i.e., it neither leans as far anteriorly as in callitrichines nor does it stand as vertically as Cebus; 4) upper and lower molars wore down rapidly in life, suggesting a herbivorous diet and the possibility of terrestriality; and 5) dental eruptive sequence is the same as in extant Aotus. As a whole, the dentition of Branisella is very similar to that of Proteopithecus from the Late Eocene of Fayum, Egypt, except in the lower canine morphology, suggesting a close phyletic relationship between them. The origin and early diversification of platyrrhine monkeys might have occurred on the African continent before crossing the Atlantic Ocean.

Animals↗

PubMed2004

Role of carnivores in the accumulation of the Sterkfontein Member 4 hominid assemblage: a taphonomic reassessment of the complete hominid fossil sample (1936-1999).

New taphonomic data on the Sterkfontein Member 4 (South Africa) fossil hominid assemblage are presented. The previous estimate of hominid individuals represented in the deposit (45) is increased to 87. New minimum numbers of hominid skeletal elements are provided, and incidences of bone surface damage inflicted by prehistoric biological agents are summarized. The hominid sample from Member 4 is composed predominately of gnathic remains and has a paucity of postcrania. This dearth of postcrania limits, to some extent, inferences about the formation of the Sterkfontein assemblage. However, carnivore tooth marks on some fossil specimens and an overall broad similarity in patterns of skeletal part representation between Sterkfontein and primate bone assemblages created by extant carnivores suggest that carnivores did have some involvement in the accumulation of the fossil hominid assemblage. Thus, this study provides support for the "carnivore-collecting hypothesis" of Brain (Brain [1981] The Hunters or the Hunted? Chicago: University of Chicago Press), which implicates large carnivores as prominent collecting agents of hominid body parts in Sterkfontein Member 4. Evidence of bone surface damage is, however, too scant to make confident inferences about specific carnivore taxon/taxa involved in hominid bone collection at the site.

Animals↗

PubMed1986

New fossil anthropoids from the middle Miocene of East Africa and their bearing on the origin of the oreopithecidae.

Recent paleontological collections at the middle Miocene locality of Maboko Island in Kenya, dated at 15-16 million years, have yielded numerous new specimens belonging to at least five species of fossil anthropoids. The most common species of ape at the site, a medium-sized primate with a very distinctive dental morphology, clearly represents a previously undescribed taxon. When compared with other Miocene anthropoids from East Africa, it has its closest affinities with the poorly known species Rangwapithecus vancouveringi from the early Miocene locality of Rusinga Island. The species from Maboko Island is described here as belonging to a new genus of fossil anthropoid, to which "Rangwapithecus" vancouveringi is also referred. The new genus has a highly distinctive suite of derived characters of its molars and premolars, which it shares with Oreopithecus bambolii from the late Miocene of Europe. These synapomorphies indicate a close phyletic relationship between the East African species and Oreopithecus and form the basis for the inclusion of these taxa in a single family, the Oreopithecidae Schwalbe, 1915. In many respects, however, the East African forms are more conservative than Oreopithecus, and in a general sense they can be regarded as an intermediate grade between Oreopithecus and the more generalized early Miocene catarrhines, the proconsuloids. There is, therefore, good fossil evidence to indicate that the origins of the Oreopithecidae can be traced back to the early Miocene of Africa.

Animals↗

PubMed2006

Size and shape dimorphism in great ape mandibles and implications for fossil species recognition.

Sexual dimorphism is an important source of morphological variation, and species differences in dimorphism may be reflected in magnitude, pattern, or both. While the extant great apes are commonly used as a reference sample for distinguishing between sexual dimorphism and intertaxic variation in the fossil record, few studies have evaluated mandibular dimorphism in these taxa. In this study, percentage, degree, and pattern of mandibular dimorphism are evaluated in Pongo, Gorilla, and Pan. Mandibular dimorphism patterns are explored to determine the extent to which such patterns accurately track great ape phylogeny. Pattern stability is assessed to determine whether there are stable patterns of mandibular size and shape dimorphism that may be usefully applied to hominoid or hominid fossil species recognition studies. Finally, the established patterns of dimorphism are used to address recent debates surrounding great ape taxonomy. Results demonstrate that mandibular dimorphism is universally expressed in size, but only Pongo and Gorilla exhibit shape dimorphism. Pattern similarity tends to be greater between subspecies of the same species than between higher-order taxa, suggesting that within the great apes, there is a relationship between dimorphism pattern and phylogeny. However, this relationship is not exact, given that dimorphism patterns are weakly correlated between some closely related taxa, while great ape subspecies may be highly correlated with taxa belonging to other species or genera. Furthermore, dimorphism patterns are not significantly correlated between great ape genera, even between Gorilla and Pan. Dimorphism patterns are more stable in Gorilla and Pongo as compared to Pan, but there is little pattern stability between species or genera. Importantly, few variables differ significantly between taxa that simultaneously show consistently relatively low levels of dimorphism and low levels of variation within taxa. Combined, these findings indicate that mandibular dimorphism patterns can and do vary considerably, even among closely related species, and suggest that it would be difficult to employ great ape mandibular dimorphism patterns for purposes of distinguishing between intra- and interspecies variation in fossil samples. Finally, the degree of pattern similarity in mandibular dimorphism is lower than previously observed by others for craniofacial dimorphism. Thus, the possibility cannot be ruled out that patterns of craniofacial dimorphism in great apes may be associated with a stronger phylogenetic signal than are patterns of mandibular dimorphism.

Animals↗

PubMed2001

Fossil record of echinoderm regeneration with special regard to crinoids.

Regeneration of skeletal parts of fossil echinoderms is reviewed. Among regenerations of various fossil echinoderms, those of crinoids are most common and many examples have been reported. Mesozoic and Cenozoic crinoids, the subclass Articulata, are characterized by the dominance of muscular articulations in the arms and they have only a small number of ligamentary articulations in localized positions that are specialized for autotomy. The dominance of muscular articulations is most conspicuous in the family Isocrinidae and comatulid (stalkless) crinoids. Most of the regenerated arms of articulate crinoids start on this ligamentary articulation. In contrast, most Paleozoic crinoids have many more ligamentary articulations and fewer muscular articulations in their arms than the Mesozoic to Recent crinoids. The ligamentary articulations of Paleozoic crinoids were probably not capable of autotomy. Fossil and recent stalked crinoids provide data on the degree and style of regeneration after loss of body parts. If the aboral nerve center in the basal part of crown is retained, the entire calyx and arms can be regenerated. In contrast, if the aboral nerve center is lost and only the stalk is preserved, some skeletal parts can only be generated imperfectly and irregularly. This type of imperfect regeneration is better termed as overgrowth.

Animals↗

PubMed1993

Preservation of biological information in thermal spring deposits: developing a strategy for the search for fossil life on Mars.

Current interpretations of the early history of Mars suggest many similarities with the early Earth and therefore raise the possibility that the Archean and Proterozoic history of life on Earth could have a counterpart on Mars. Terrestrial experience suggests that, with techniques that can be employed remotely, ancient springs, including thermal springs, could well yield important information. By delivering water and various dissolved species to the sunlit surface of Mars, springs very likely created an environment suitable for life, which could have been difficult, if not impossible, to attain elsewhere. The chemical and temperature gradients associated with thermal springs sort organisms into sharply delineated, distinctive and different communities, and so diverse organisms are concentrated into relatively small areas in a predictable and informative fashion. A wide range of metabolic strategies are concentrated into small areas, thus furnishing a useful and representative sampling of the existing biota. Mineral-charged springwaters frequently deposit chemical precipitates of silica and/or carbonate which incorporate microorganisms and preserve them as fossils. The juxtaposition of stream valley headwaters with volcanoes and impact craters on Mars strongly implies that subsurface heating of groundwater created thermal springs. On Earth, thermal springs create distinctive geomorphic features and chemical signatures which can be detected by remote sensing. Spring deposits can be quite different chemically from adjacent rocks. Individual springs can be hundreds of meters wide, and complexes of springs occupy areas up to several kilometers wide. Benthic microbial mats and the resultant stromatolites occupy a large fraction of the available area. The relatively high densities of fossils and microbial mat fabrics within these deposits make them highly prospective in any search for morphological evidence of life, and there are examples of microbial fossils in spring deposits as old as 300 Myr.

Bacteria↗

PubMed1999

Artificial cranial deformation and fossil Australians revisited.

Based on cranial characters shared by Homo erectus in Java and Homo sapiens in Australia, Australasia is widely considered the strongest case for a regional origin of modern humans. However, artificial vault deformation has been suggested to be the cause of "archaic" characters such as frontal recession in key fossil Australian crania. We use log-log plots of cranial arc versus chord measurements and we score nonmetric traits often thought to be associated with artificial deformation to make systematic comparisons across groups and deformation types to identify universal consequences of artificial deformation. Based on our large comparative sample (n = 588) apparatus-deformed crania have flatter frontals and occipitals and usually more angulated parietals in the sagittal plane than undeformed crania, regardless of deformation type. Fossil Australian samples exhibit evidence of both undeformed and deformed individuals. The sample from Coobool Creek provides evidence that undeformed individuals had more rounded frontals than recent Australians. However, many individuals from Coobool Creek, Kow Swamp, and Nacurrie exhibit modification of one or more cranial contours. The Kow Swamp individuals in particular plot with deformed crania from all regions. In addition, the frequency of hyperostotic traits such as bregmatic eminence, metopic and sagittal keels in H. sapiens is influenced by both artificial deformation and pathological hypervascularity/hyperostosis. Thus it is unwise to use cranial contours and these nonmetric traits to infer genetic relatedness between Fossil Australians and Indonesian H. erectus.

Animals↗

PubMed2000

The depositional context of the early upper paleolithic human fossils from the Koneprusy (Zlatý kůn) and Mladec caves, Czech republic.

The caves of Mladec I and II (Moravia) and Koneprusy (Bohemia) are principal hominid Early Upper Paleolithic sites in Central Europe that require a complex reconsideration from several viewpoints. The focus of this paper is on the depositional context of human fossils, which is clearer from the documentation of Koneprusy, excavated during the 1950s, than from the early reports about Mladec. Both caves are multi-floor underground karstic systems penetrated by vertical fissures and chimneys, where the fossils were found in restricted areas, related to debris cones accumulated under the chimneys. These associations are confirmed using Surfer reconstruction of the original fillings. It appears certain for Koneprusy and highly probable for Mladec that the fossils fell in through the chimneys. This does not mean that living animals and humans never entered the interior of the caves (traces of gnawing by hyenas are visible), but it makes it unlikely that the human paleontological accumulations were the result of human activity within the cave chambers.

Animals↗

PubMed1996

Evolution of the diatoms (Bacillariophyta). IV. A reconstruction of their age from small subunit rRNA coding regions and the fossil record.

Small subunit ribosomal RNA (ssu rRNA) coding regions from 30 diatoms, 3 oomycetes, and 6 pelagophytes were used to construct linearized trees, maximum-likelihood trees, and neighbor-joining trees inferred from both unweighted and weighted distances. Stochastic accumulation of sequence substitutions among the diatoms was assessed with relative rate tests. Pennate diatoms evolved relatively slowly but within the limits set by a stochastic model; centric diatoms exceeded those limits. A rate distribution test was devised to identify those taxa showing an aberrant distribution of base substitutions within the ssu rRNA coding region. First appearance dates of diatom taxa from the fossil record were regressed against their corresponding branch lengths to infer the average and earliest possible age for the origin of the diatoms, the pennate diatoms, and the centric diatom order Thalassiosirales. Our most lenient age estimate (based on the median-evolving diatom taxon in the maximum-likelihood tree or on the average branch length in a linearized tree) suggests that their average age is approximately 164-166 Ma, which is close to their earliest fossil record. Both calculations suggest that it is unlikely that diatoms existed prior to 238-266 Ma. Rate variation among the diatoms' ssu rRNA coding regions and uncertainties associated with the origin of extant taxa in the fossil record contribute significantly to the variation in age estimates obtained. Different evolutionary models and the exclusion of fast or slow evolving taxa did not significantly affect age estimates; however, the inclusion of aberrantly fast evolving taxa did. Our molecular clock calibrations indicate that the rRNA coding regions in the diatoms are evolving at approximately 1% per 18 to 26 Ma, which is the fastest substitution rate reported in any pro- or eukaryotic group of organisms to date.

Biological Evolution↗

PubMed1986

Community living long before man: fossil and living microbial mats and early life.

Microbial mats are layered communities of bacteria that form cohesive structures, some of which are preserved in sedimentary rocks as stromatolites. Certain rocks, approximately three and a half thousand million years old and representing the oldest known fossils, are interpreted to derive from microbial mats and to contain fossils of microorganisms. Modern microbial mats (such as the one described here from Matanzas, Cuba) and their fossil counterparts are of great interest in the interpretation of early life on Earth. Since examination of microbial mats and stromatolites increases our understanding of long-term stability and change, within the global environment, such structures should be protected wherever possible as natural science preserves. Furthermore, since they have existed virtually from the time of life's origin, microbial mats have developed exemplary mechanisms of local community persistence and may even play roles in the larger global environment that we do not understand.

Bacteria↗

PubMed1991

Fossils as keys to evolution in fungi.

Both flagellated and nonflagellated fungi have an extensive fossil record, which is, however, unevenly documented and often difficult to interpret. Recent work on Silurian, Devonian and Carboniferous terrestrial assemblages has provided plausible evidence for all major groups of extant fungi in the Paleozoic. Key events in fungal macroevolution thus probably took place in the early Paleozoic or the late Precambrian, and the likelihood of finding definitive fossil evidence for them is small. The fossil record also provides evidence for morphological conservatism and early establishment of a spectrum of intimate associations between fungi and vascular plants. A model for the origin of terrestrial fungi involving two distinct lines of biotrophs in lichen-like symbioses with algae is proposed.

Biological Evolution↗

PubMed1993

Classification of organisms: living and fossil.

The classification advanced herein provides a framework to which any organism can be readily placed and offers comprehensive coverage of the entire biological spectrum. The viruses are incorporated as a kingdom of organisms and a rationale advanced for a 6-kingdom system. Many seldom-classified fossil organisms are included, with a significant number of them classified at an advanced level. Individual phyla are recognized for the fossil genera Tribrachidium, Amiskwia, Dinomischus, Anomalocaris, Tullimonstrum, Hallucigenia, Opabinia and Pikaia. Other seldom-recognized phyla include viruses, conularids, loriciferans, tentaculites, hyoliths, scleritophores, myzostomans, acorn worms, conodonts, monoblastozoans and volborthellids. The notion that failures (geologically) cannot be phyla is rejected. A system of kingdom-related and rank-related suffixes is incorporated with the flexible opportunity, if deemed necessary, to advance or reduce taxa by re-suffixing. Other features of the complete classification of Anderson (Classification of Organisms: Living and Fossil, Golden Crowns Press, Lancaster, OH, 1992) include the elimination of duplicate taxa, incorporation of geologic ranges and number of species for many groups, and extensive usage of common names, which are completely indexed.

Animal Population Groups↗

PubMed2005

Mandibular fossa of fossil Australians.

Many questions about the skeletal adaptations and morphology of hunter-gatherers on the Australian continent remain unanswered. One anatomical region receiving little research in Australian fossils to date is the mandibular fossa. Here we report a study of three size dimensions, three shape indices and three morphological (non-metric) features of the mandibular fossa in 11 fossil Australians comparing them with modern Australo-Melanesian samples. We find broad similarities in past and modern populations in this region. Early and modern Australians and modern Papua New Guineans have elongate, broad and shallow fossae. All three populations show similarity in articular tubercle size, but postglenoid tubercle and entoglenoid process sizes show unexpected affinities. We also test for the possible presence of temporal trends in mandibular fossa size among fossil Australians. Our analyses indicate that none are present.

Analysis of Variance↗

PubMed2005

When Earth started blooming: insights from the fossil record.

Recent palaeobotanical studies have greatly increased the quantity and quality of information available about the structure and relationships of Cretaceous angiosperms. Discoveries of extremely well preserved Cretaceous flowers have been especially informative and, combined with results from phylogenetic analyses of extant angiosperms (based mainly on molecular sequence data), have greatly clarified important aspects of early angiosperm diversification. Nevertheless, many questions still persist. The phylogenetic origin of the group itself remains as enigmatic as ever and, in some cases, newly introduced techniques from molecular biology have given confusing results. In particular, relationships between the five groups of extant seed plants remain uncertain, and it has sometimes proved difficult to reconcile estimates of the time of divergence between extant lineages made using a 'molecular clock' with the fossil record. One result, however, is becoming increasingly clear: a great deal of angiosperm diversity is extinct. Some groups of angiosperms were evidently more diverse in the past than they are today. In other cases, fossils defy assignment to extant groups at the family level or below. This raises the possibility that evolutionary conclusions based solely upon extant taxa that are merely relics of groups that were once much more diverse might be misled by the effects of extinction. It also introduces the possibility that some early enigmatic fossils might represent lineages that diverged from the main line of angiosperm evolution below the most recent common ancestor of all extant taxa. These, and other questions, are among those that need to be addressed by future palaeobotanical research.

Biological Evolution↗

PubMed1997

The youngest Ediacaran fossils from southern Africa.

Discovery of fossils of the Ediacara biota near the top of the Spitzkopf Member at farm Swanpunt extends the known range of these remains in Namibia more than 600 m to near the sub-Cambrian unconformity. The fossiliferous beds occur approximately 100 m above a volcanic ash dated at 543 +/- 1 Ma, and thus may be the youngest Proterozoic Ediacara-type fossils reported anywhere in the world. Fossils are preserved within and on the tops of dm-thick beds of storm-deposited sandstone at two stratigraphic levels; the environment is interpreted as open marine, generally calm but with episodic disruptions by storm waves, and probably within the euphotic zone. The presence of Pteridinium carolinaense (St. Jean), which is also known from the classic sections in Ediacara and the White Sea among others, reinforces evidence from geochronology and chemostratigraphy that the Swartpunt section is terminal Neoproterozoic in age. The new genus and species Swartpuntia germsi is a large, multifoliate frond that exhibits at least three quilted petaloids. Macroscopically, Swartpuntia resembles Pteridinium and Ediacara-type fronds such as Charniodiscus traditionally interpreted as Cnidaria, whereas microscopically it exhibits segmentation that is remarkably similar to that of the putative worm Dickinsonia. Combination of diagnostic characters of these supposedly disparate groups in a single species suggests that many species of quilted Ediacaran organisms were more similar to each other than they were to any modern groups, and provides support for the concept of the "Vendobionta" as a late Neoproterozoic group of mainly multifoliate organisms with a distinctive quilted segmentation.

Animals↗

PubMed1996

Fossil preservation and the stratigraphic ranges of taxa.

The incompleteness of the fossil record hinders the inference of evolutionary rates and patterns. Here, we derive relationships among true taxonomic durations, preservation probability, and observed taxonomic ranges. We use these relationships to estimate original distributions of taxonomic durations, preservation probability, and completeness (proportion of taxa preserved), given only the observed ranges. No data on occurrences within the ranges of taxa are required. When preservation is random and the original distribution of durations is exponential, the inference of durations, preservability, and completeness is exact. However, reasonable approximations are possible given non-exponential duration distributions and temporal and taxonomic variation in preservability. Thus, the approaches we describe have great potential in studies of taphonomy, evolutionary rates and patterns, and genealogy. Analyses of Upper Cambrian-Lower Ordovician trilobite species, Paleozoic crinoid genera, Jurassic bivalve species, and Cenozoic mammal species yield the following results: (1) The preservation probability inferred from stratigraphic ranges alone agrees with that inferred from the analysis of stratigraphic gaps when data on the latter are available. (2) Whereas median durations based on simple tabulations of observed ranges are biased by stratigraphic resolution, our estimates of median duration, extinction rate, and completeness are not biased.(3) The shorter geologic ranges of mammalian species relative to those of bivalves cannot be attributed to a difference in preservation potential. However, we cannot rule out the contribution of taxonomic practice to this difference. (4) In the groups studied, completeness (proportion of species [trilobites, bivalves, mammals] or genera [crinoids] preserved) ranges from 60% to 90%. The higher estimates of completeness at smaller geographic scales support previous suggestions that the incompleteness of the fossil record reflects loss of fossiliferous rock more than failure of species to enter the fossil record in the first place.

Animals↗

PubMed2003

The oldest fossil myxogastroid slime mould.

A piece of Baltic amber (Tertiary, Eocene) contains a sporocarp of a slime mould which is assigned to the recent genus Arcyria and described as A. sulcata sp. nov. Apart from a fossil stemonitoid myxomycete, there are no further unambiguous fossil records of slime moulds and therefore the fossil gives new insights into the evolutionary history of the Myxomycetes.

Biological Evolution↗

PubMed2003

Recognizing and interpreting the fossils of early eukaryotes.

Using molecular sequence data, biologists can generate hypotheses of protistan phylogeny and divergence times. Fossils, however, provide our only direct constraints on the timing and environmental context of early eukaryotic diversification. For this reason, recognition of eukaryotic fossils in Proterozoic rocks is key to the integration of geological and comparative biological perspectives on protistan evolution. Microfossils preserved in shales of the ca. 1500 Ma Roper Group, northern Australia, display characters that ally them to the Eucarya, but, at present, attribution to any particular protistan clade is uncertain. Continuing research on wall ultrastructure and microchemistry promises new insights into the nature and systematic relationships of early eukaryotic fossils.

Animals↗