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At least 109 records · Page 6Linked to original sources

PubMed2001

A three-dimensionally preserved fossil polychaete worm from the Silurian of Herefordshire, England.

Polychaete body fossils are rare, and are almost invariably compressed and too poorly preserved for meaningful comparison with extant forms. We here describe Kenostrychus clementsi gen. et sp. nov. from the Silurian Herefordshire Konservat-Lagerstätte of England, in which three-dimensional external morphology is preserved with a fidelity unprecedented among fossil polychaetes. The fossils, which are preserved in calcite, were serially ground and photographed at 30 microm intervals to produce computer-generated reconstructions of the original external surface. The new genus has a generalized polychaete morphology with large biramous parapodia, unspecialized anterior segments and a small prostomium with median and lateral antennae and ventral prostomial palps. Cirriform branchiae arise from the ventral surface of each notopodium, and may be homologous with the inter-ramal branchiae of the extant nephtyids. Through cladistic analysis, Kenostrychus is interpreted as a member of a stem group of either the Phyllodocida or the Aciculata (Phyllodocida + Eunicida). Direct comparison with other fossil forms is difficult, but hints that inter-ramal respiratory structures may be primitive within the Phyllodocida and/or the Aciculata.

Animals↗

PubMed1999

Preservation of key biomolecules in the fossil record: current knowledge and future challenges.

We have developed a model based on the analyses of modern and Pleistocene eggshells and mammalian bones which can be used to understand the preservation of amino acids and other important biomolecules such as DNA in fossil specimens. The model is based on the following series of diagenetic reactions and processes involving amino acids: the hydrolysis of proteins and the subsequent loss of hydrolysis products from the fossil matrix with increasing geologic age; the racemization of amino acids which produces totally racemized amino acids in 10(5)-10(6) years in most environments on the Earth; the introduction of contaminants into the fossil that lowers the enantiomeric (D:L) ratios produced via racemization; and the condensation reactions between amino acids, as well as other compounds with primary amino groups, and sugars which yield humic acid-like polymers. This model was used to evaluate whether useful amino acid and DNA sequence information is preserved in a variety of human, amber-entombed insect and dinosaur specimens. Most skeletal remains of evolutionary interest with respect to the origin of modern humans are unlikely to preserve useful biomolecular information although those from high latitude sites may be an exception. Amber-entombed insects contain well-preserved unracemized amino acids, apparently because of the anhydrous nature of the amber matrix, and thus may contain DNA fragments which have retained meaningful genetic information. Dinosaur specimens contain mainly exogenous amino acids, although traces of endogenous amino acids may be present in some cases. Future ancient biomolecule research which takes advantage of new methologies involving, for example, humic acid cleaving reagents and microchip-based DNA-protein detection and sequencing, along with investigations of very slow biomolecule diagenetic reactions such as the racemization of isoleucine at the beta-carbon, will lead to further enhancements of our understanding of biomolecule preservation in the fossil record.

Amino Acids↗

PubMedDate not supplied

Fossilized embryos are widespread but the record is temporally and taxonomically biased.

We report new discoveries of embryos and egg capsules from the Lower Cambrian of Siberia, Middle Cambrian of Australia and Lower Ordovician of North America. Together with existing records, embryos have now been recorded from four of the seven continents. However, the new discoveries highlight secular and systematic biases in the fossil record of embryonic stages. The temporal window within which the embryos and egg capsules are found is of relatively short duration; it ends in the Early Ordovician and is roughly coincident with that of typical "Orsten"-type faunas. The reduced occurrence of such fossils has been attributed to reducing levels of phosphate in marine waters during the early Paleozoic, but may also be owing to the increasing depth of sediment mixing by infaunal metazoans. Furthermore, most records younger than the earliest Cambrian are of a single kind-large eggs and embryos of the priapulid-like scalidophoran Markuelia. We explore alternative explanations for the low taxonomic diversity of embryos recovered thus far, including sampling, size, anatomy, ecology, and environment, concluding that the preponderance of Markuelia embryos is due to its precocious development of cuticle at an embryonic stage, predisposing it to preservation through action as a substrate on which microbially mediated precipitation of authigenic calcium phosphate may occur. The fossil record of embryos may be limited to a late Neoproterozoic to early Ordovician snapshot that is subject to dramatic systematic bias. Together, these biases must be considered seriously in attempts to use the fossil record to arbitrate between hypotheses of developmental and life history evolution implicated in the origin of metazoan clades.

Animals↗

PubMed1992

DNA sequences from a fossil termite in Oligo-Miocene amber and their phylogenetic implications.

DNA was extracted from the fossil termite Mastotermes electrodominicus preserved in Oligo-Miocene amber (25 million to 30 million years old). Fragments of mitochondrial [16S ribosomal DNA (rDNA)] and nuclear (18S rDNA) genes were amplified by polymerase chain reaction. Phylogenetic analysis of fossil and extant 18S rDNA confirmed morphological cladistic analyses of living dictyopterans (termites, cockroaches, and mantids). The fossil termite shares several sequence attributes with Mastotermes darwiniensis. Addition of this fossil to living-species phylogeny is required to substantiate Mastotermes monophyly and affects molecular phylogenetic hypotheses of termites in this, the oldest DNA yet characterized.

Animals↗

PubMedDate not supplied

A comparative study of adult facial morphology and its ontogeny in the fossil macaque Macaca majori from Capo Figari, Sardinia, Italy.

This study examines the morphology of the face in the fossil macaque Macaca majori from Capo Figari (north-eastern Sardinia, Italy) in a comparative ontogenetic context. Thus, a fairly complete face from an adult representative of this fossil species is compared with 3 extant macaque species: Macaca sylvanus (of which species it is questioned whether it is a subspecies, M. sylvanus majori), Macaca mulatta and Macaca fascicularis. Additional incomplete subadult and adult specimens are also examined in order to compare their facial ontogeny with that of the same living species. The comparisons are based on facial landmark data and are undertaken using geometric morphometric methods. These studies indicate that the adult facial morphology and ontogeny of face size and shape in M. majori share much in common with extant macaque species. However, the adult M. majori face displays some unique morphological features, in particular with regard to lateral flaring and relative size of the zygomatic roots. From the study of a limited sample of fossils there is an indication that this flaring arises during postnatal growth, and in consequence the ontogeny of the face of this fossil species may be different from that of M. sylvanus and the other macaque species included in this analysis. From these studies, we conclude that M. majori shows differences in adult facial morphology and possibly in ontogeny from M. sylvanus compatible with a specific rather than subspecific distinction.

Animals↗

PubMed2002

Morphology of the hallucial phalanges in extant anthropoids and fossil hominoids.

Pedal phalanges of living anthropoids and several Miocene fossil hominoid taxa were studied to reveal functional adaptations of living anthropoid feet and to infer positional behavior of fossil hominoids. Among the examined living anthropoids, Pan has a very developed (long and robust) hallux. Proconsul and Nacholapithecus, a large hominoid from Nachola, northern Kenya, display a moderately long hallux like Alouatta and Cebus, suggesting the well-developed capability of a hallux-assisted power grip. Allometric analyses revealed that the Miocene hominoids examined (mainly from East Africa) as a whole displayed a different scaling pattern about the width of the proximal articular surface of the hallucial terminal phalanx from that of living anthropoids. Larger-sized hominoids display a wider articular surface than comparable-sized living anthropoids while smaller-sized fossil hominoids do the reverse. Such a difference was less marked for the height of the articular surface. These results may suggest that positional adaptations of Miocene hominoids are not merely resultants of a common body size function that is observed in living anthropods. The wide articular surface of fossil hominoid hallucial terminal phalanges suggests an adaptation for vertical climbing and clinging, in which the hallux is kept perpendicularly to the long axis of the vertical support.

Animals↗

PubMed1997

[Determination of trace rare earth in fossil of dinosaurian egg by laser thermal lens spectrometry].

Determination of trace rare earth in fossil of dinosaurian egg by LTLS (Laser thermal lens spectrometry) is presented in this paper. The trace rare earth in fossil of dinosaurian egg was separated and concentrated with ion exchange method. The measure conditions and effect factors are discussedian. The LTLS was applied to the determination of trace rare earth in fossil of dinosaurian egg with satisfactory results. It provides the reference data for the studies on the fossil of dinosaurian egg and an analytical method for the determination of rare earth in geochemical sample.

Animals↗

PubMed1987

Cracks in fossil enamels resulting from premortem vs. postmortem events.

Vertebrate enamel preserves a record of fracture-producing strain. Fracturing during the life of the individual is potentially a source of selection for stronger enamel in the course of evolution. To determine if it is possible to recognize such fractures in fossil enamel, cracks in a variety of fossil materials, including enamel-covered holostean scales, crocodilian teeth, theropod and hadrosaurid dinosaur teeth, and mammalian teeth were examined. Cracks that occurred during the life of the individual could be recognized by abrasive wear on edges exposed at the surface of the enamel in areas worn by oral or locomotor abrasion. Certain distinctive crack patterns were identified as results of specific stress states occurring during life. Transverse cracks on the anterior parts of Lepisosteus scales were probably caused by external loading. Hertzian cracks and shallow, arcuate, lateral cracks on the occlusal edges of tooth enamel appear to be caused by stress concentrating impacts. Horizontal cracks arranged asymmetrically on the sides of conical teeth were reproduced in models subjected to bending stresses. Oblique cracks near the tips of conical fossil teeth were produced in models by oblique loads near the tip. Vertical cracks around cylindrical or conical tooth surfaces may be caused by several different sources of stress, including lateral "wind" loads and vertical "snow" loads. Of the postmortem causes of fracturing of fossil enamel, drying cracks seem to be the most important. Experimental drying produced from 25% to 50% of the cracks in dry teeth.

Alligators and Crocodiles↗

PubMed1993

Homologies in the fossil record: the middle ear as a test case.

This paper examines the middle ear of fossil living animals in terms of the homologies which have been drawn between its parts in different vertebrate groups. Seven homologies are considered: 1, the middle ear cavity/spiracular pouch; 2, the stapes/hyomandibula; 3, the stapedial/hyomandibular processes; 4 the tympanic membrane; 5, the otic notch; 6, the fenestra ovalis; 7, and the stapedial/hyomandibular foramen. The reasons leading to assessments of homology are reviewed. Homologies 1 and 2, based largely on embryological evidence, are fairly robust, though there are arguments about the details. Homologies 3, 4 and 5 stem from ideas about early tetrapod evolution, and were influenced by contingent factors including the order and time of discovery of early fossil taxa, and perceptions of their phylogeny which resulted from this. They were also influenced by ideas of the evolution of terrestriality among tetrapods. Most of the conceptions have been overturned in recent years by new fossil discoveries and new ways of looking at old data. Homology 6 has been little considered. One possible hypothesis, placed in a strictly 'archetypal' theoretical framework has been ignored but deserves consideration on other grounds. Homology 7 depends on how tetrapods are characterised, not a question which has posed difficulties until recently, but which is likely to with the discovery of intermediate fossil forms.

Animals↗

PubMed2001

Speciation in the fossil record.

It is easy to claim that the fossil record says nothing about speciation because the biological species concept (which relies on interbreeding) cannot be applied to it and genetic studies cannot be carried out on it. However, fossilized organisms are often preserved in sufficient abundance for populations of intergrading morphs to be recognized, which, by analogy with modern populations, are probably biological species. Moreover, the fossil record is our only reliable documentation of the sequence of past events over long time intervals: the processes of speciation are generally too slow to be observed directly, and permanent reproductive isolation can only be verified with hindsight. Recent work has shown that some parts of the fossil record are astonishingly complete and well documented, and patterns of lineage splitting can be examined in detail. Marine plankton appear to show gradual speciation, with subsequent morphological differentiation of lineages taking up to 500000 years to occur. Marine invertebrates and vertebrates more commonly show punctuated patterns, with periods of rapid speciation followed by long-term stasis of species lineages.

Journal Article↗

PubMed1999

Phylogeny of Marsileaceous Ferns and Relationships of the Fossil Hydropteris pinnata Reconsidered.

Recent phylogenetic studies have provided compelling evidence that confirms the once disputed hypothesis of monophyly for heterosporous leptosporangiate ferns (Marsileaceae and Salviniaceae). Hypotheses for relationships among the three genera of Marsileaceae (Marsilea, Regnellidium, and Pilularia), however, have continued to be in conflict. The phylogeny of Marsileaceae is investigated here using information from morphology and rbcL sequence data. In addition, relationships among all heterosporous ferns, including the whole-plant fossil Hydropteris pinnata are reconsidered. Data sets of 71 morphological and 1239 rbcL characters for 23 leptosporangiate ferns, including eight heterosporous ingroup taxa and 15 homosporous outgroup taxa, were subjected to maximum parsimony analysis. Morphological analyses were carried out both with and without the fossil Hydropteris, and it was excluded from all analyses with rbcL data. An annotated list of the 71 morphological characters is provided in the appendix. For comparative purposes, the Rothwell and Stockey (1994) data set was also reanalyzed here. The best estimate of phylogenetic relationships for Marsileaceae in all analyses is that Pilularia and Regnellidium are sister taxa and Marsilea is sister to that clade. Morphological synapomorphies for various nodes are discussed. Analyses that included Hydropteris resulted in two most-parsimonious trees that differ only in the placement of the fossil. One topology is identical to the relationship found by Rothwell and Stockey (1994), placing the fossil sister to the Azolla plus Salvinia clade. The alternative topology places Hydropteris as the most basal member of the heterosporous fern clade. Equivocal interpretations for character evolution in heterosporous ferns are discussed in the context of these two most-parsimonious trees. Because of the observed degree of character ambiguity, the phylogenetic placement of Hydropteris is best viewed as unresolved, and recognition of the suborder Hydropteridineae, as circumscribed by Rothwell and Stockey (1994), is regarded as premature. The two competing hypotheses of relationships for heterosporous ferns are also compared with the known temporal distribution of relevant taxa. Stratigraphic fit of the phylogenetic estimates is measured by using the Stratigraphic Consistency Index and by comparison with minimum divergence times.

Journal Article↗

PubMed1999

The Phylogenetic Affinities of Nothofagus (Nothofagaceae) Leaf Fossils based on Combined Molecular and Morphological Data.

The phylogenetic placements of leaf fossils of Nothofagus (Nothofagaceae) were determined using parsimony analyses of molecular and morphological data for extant species combined with morphological data for fossils. Placement was possible for only seven of the 30 or so described fossil species of Nothofagus because only these had sufficiently good preservation of both cuticular and leaf architectural characters. In combined analyses of morphology and molecular data, leaf cuticular characters showed little homoplasy. In contrast, many architectural characters, including some leaf margin and venation characters, showed high homoplasy, making it difficult or impossible to accurately determine the phylogenetic affinities of impression fossils of this genus.

Journal Article↗

PubMed2001

Assessing the potential for the stomatal characters of extant and fossil Ginkgo leaves to signal atmospheric CO2 change.

The stomatal density and index of fossil Ginkgo leaves (Early Jurassic to Early Cretaceous) have been investigated to test whether these plant fossils provide evidence for CO(2)-rich atmosphere in the Mesozoic. We first assessed five sources of natural variation in the stomatal density and index of extant Gingko biloba leaves: (1) timing of leaf maturation, (2) young vs. fully developed leaves, (3) short shoots vs. long shoots, (4) position in the canopy, and (5) male vs. female trees. Our analysis indicated that some significant differences in leaf stomatal density and index were evident arising from these considerations. However, this variability was considerably less than the difference in leaf stomatal density and index between modern and fossil samples, with the stomatal index of four species of Mesozoic Ginkgo (G. coriacea, G. huttoni, G. yimaensis, and G. obrutschewii) 60-40% lower than the modern values recorded in this study for extant G. biloba. Calculated as stomatal ratios (the stomatal index of the fossil leaves relative to the modern value), the values generally tracked the CO(2) variations predicted by a long-term carbon cycle model confirming the utility of this plant group to provide a reasonable measure of ancient atmospheric CO(2) change.

Journal Article↗

PubMed2002

[Archaeological application of the Raman microprobe to the non-destructive identification of dinosaur fossil from Yunnan Wuding].

Selected ancient Dinosaur fossils (about a hundred million ago) from Wuding, Yunnan, pilot were studied by micro-Raman spectroscopy, atomic emissive spectrum and polarization microscopic analysis. Raman experimental results found out the primary compounds of fossil surface and section are calcite (CaCO3), and are not others. Analysis of atomic emissive spectrum indicated that main elements of fossils are calcium (> 10%), silicon (5.0%), phosphor (4.0%) and iron (1.0%), rare elements example of iridium (Ir) and thorium (Th) are not found in testing. Complementary studies by atomic emissive spectrum and polarization microscope found that besides calcite (CaCO3), SiO2.nH2O, which is not crystal, is contained in the examples of the fossils. Main composition data taken from both the atomic emissive spectrum, microscopic photograph and Raman spectroscopy are in agreement.

English Abstract↗

PubMed1996

Chin morphology and sexual dimorphism in the fossil hominid mandible sample from Klasies River Mouth.

The site of Klasies River Mouth (KRM) in South Africa has produced a small sample of early Upper Pleistocene hominid remains that have been a focus for discussions of the origins of modern humans. Despite certain primitive characteristics exhibited by these fossils, proponents of a single recent origin have attributed them to early modern humans. Critics of this hypothesis have emphasized the significance of the archaic features evident in this sample, including the absence of pronounced chins among the mandibular specimens. This study compares the size range and chin morphology exhibited by the KRM mandibles with that of Neandertals, Upper Pleistocene humans, and recent humans. The extreme sexual dimorphism documented among the KRM fossils reflects the presence of a very small individual, and previous efforts to classify the KRM sample as archaic on the basis of their robusticity have failed to address the significance of this diminutive hominid. While each KRM fossil falls within the 95% envelope of variability established for chin development in a comparative modern sample, a similarly low frequency of pronounced chins is very unlikely to be found in any recent human population. The morphological pattern of the KRM mandibles is clearly distinct from that of Neandertals and of recent humans.

Animals↗

PubMed1997

Cranial shape in fruit, nectar, and exudate feeders: implications for interpreting the fossil record.

At least 29 species of fossil primates have been referred to fruit, nectar, and/or exudate feeding dietary niches. Many studies have detailed the morphological correlates of fruit feeding in comparison to insectivory and folivory. In contrast, few studies have sought to differentiate the morphological correlates of fruit feeding from those of nectar and exudate feeding. This study investigates the differences between fruit, nectar, and exudate feeders using 22 cranial and dentary shape variables representing 28 species of living marsupials, bats, and primates. Discriminant function analysis is used to investigate the differences between these dietary categories using both the complete data set and a reduced data set composed of variables that might reasonably be available from fragmentary fossil material. The success rates of post-hoc classifications are 94 and 88%, respectively. These results demonstrate that it is possible to discriminate among fruit, nectar, and exudate feeders among fossil taxa with a reasonable degree of certainty using the data and techniques outlined here. Nectar feeders exhibit a unique combination of features that are associated with reduced masticatory strength and their role as pollination agents. Exudate feeder skulls and dentaries exhibit a combination of features that reflect the high stresses encountered by the anterior dentition through bark gouging behavior. Fruit feeders are morphologically diverse, exhibiting cranial and mandibular shape values that overlap with both nectar and exudate feeders. It is suggested that this diversity reflects the variety of physical properties represented among fruits, and the tendency for individual frugivore species to specialize on particular fruits.

Animals↗

PubMed1997

Immunospecificity of albumin detected in 1.6 million-year-old fossils from Venta Micena in Orce, Granada, Spain.

The Orce skull fragment from southern Spain, dated at 1.6 Myr, has been a subject of heated controversy since it was first discovered in 1982. If it is hominid, as its discoverers contend, it is by far the oldest fossil hominid yet found in western Europe and implies that human populations settled this region much earlier than was previously realized. Numerous stone artifacts found at the Orce sites provide evidence that hominids were indeed present there in the Lower Pleistocene. Some paleontologists maintain that the 8 cm diameter occipital fragment is from a horse, not a hominid. Two independent investigations of the residual proteins in the skull were undertaken, one at the University of Granada in Spain, the other at the University of California, San Francisco. Two immunological methods of comparable sensitivity were employed for detection and species attribution of protein extracted from fossil bone: the Granada team used an enzyme-linked-immunosorbent assay (ELISA), and the UCSF team used a radioimmunoassay (RIA). Both teams obtained reactions characteristic of human albumin in the Orce skull and horse albumin in some of the horse fossils. These results support the lithic evidence that hominids were living in Andalusia 1.6 million years ago.

Albumins↗

PubMed2000

Subnasal morphological variation in fossil hominids: a reassessment based on new observations and recent developmental findings.

Quantitative and qualitative assessments of subnasal morphology in fossil hominids yield distinct patterns which have been used both to sort robust from nonrobust australopithecine taxa and to distinguish individual species. Recently, new developmental models have been applied to hominoid subnasal morphological variation. These studies require that certain features of the fossil hominid subnasal region, in particular the topography of the nasal cavity entrance and details of vomeral morphology, be reevaluated. This study does so for the robust and nonrobust australopithecines, early Homo (H. habilis/H. rudolfensis), and African H. erectus. Results reaffirm an overall similarity of the nonrobust Australopithecus subnasal morphological pattern with that of the chimpanzee. They further indicate that a vomeral insertion above the nasal surface of the premaxilla should be added to the list of traits characteristic of the robust australopithecine subnasal morphological pattern. Finally, reassessment of subnasal morphology in the early Homo and H. erectus samples from Africa suggest that these two taxa share a similar subnasal morphological pattern. This pattern consists of a smooth nasal cavity entrance, a horizontal nasal sill whose anterior edge is demarcated by a strong nasal crest, and a well-developed horizontal spine at the posterior edge of the nasal sill. Although none of the African fossil Homo specimens preserve a vomer, indirect evidence suggests that it would have inserted above the nasal sill.

Animals↗