4. Fossil hominins

2019 ◽  
pp. 38-59
Author(s):  
Bernard Wood
Keyword(s):  
Fossil Record ◽  
Habitat Preferences ◽  
Fossil Remains ◽  
Fossil Evidence ◽  
Developmental Age ◽  
Fossil Hominins

Palaeoanthropologists use many methods to work out the significance of newly discovered fossil evidence, but the first task is to assign hominin fossils to a taxon. After that researchers work out that taxon’s relationships with other fossil and living taxa, and then they infer the behaviours and habitat preferences of the taxon. ‘Fossil hominins: analysis and interpretation’ explains the workings of classification and taxonomy. It describes how whole fossils can be reconstructed from fragments; the difficulties of determining the sex and developmental age of hominin fossil remains; the different interpretations of speciation; how cladistics analysis works; and the gaps and biases in the hominin fossil record.

scholarly journals Major features of protistan evolution: controversies, problems and a few answers

2006 ◽  
Vol 29 (1) ◽  
pp. 55-80
Author(s):  
Jere H Lipps
Keyword(s):  
Fossil Record ◽  
Molecular Data ◽  
Trophic Levels ◽  
Early Earth ◽  
Huge Number ◽  
Geologic Time ◽  
Earth History ◽  
Important Development ◽  
Fossil Evidence

The major features of protist evolution are fraught with controversies, problems and few answers, especially in early Earth history. In general they are based on molecular data and fossil evidence that respectively provide a scaffold and details of eukaryotic phylogenetic and ecologic histories. 1. Their origin, inferred from molecular sequences, occurred very early (>;3Ga). They are a chimera of different symbiont-derived organelles, including possibly the nucleus. 2. The initial diversification of eukaryotes may have occurred early in geologic time. Six supergroups exist today, each with fossils known from the Proterozoic and Phanerozoic. 3. Sex, considered an important development, may have been inherited from bacteria. 4. Precambrian protists were largely pelagic cyst-bearing taxa, but benthic forms were probably quite diverse and abundant. 5. Protists gave rise to animals long before 600 Ma through the choanoflagellates, for which no fossil record exists. 6. Acritarchs and skeletonized protists radiated in the Cambrian (544-530 my). From then on, they radiated and became extinct at all the major events recorded in the metazoan fossil record. 7. Protists dominated major environments (shelves and reefs) starting with a significant radiation in the Ordovician, followed by extinctions and other radiations until most died out at the end of the Permian. 8. In the Mesozoic, new planktic protozoa and algae appeared and radiated in pelagic environments. 9. Modern protists are important at all trophic levels in the oceans and a huge number terrestrial, parasitic and symbiotic protists must have existed for much of geologic time as well. 10. The future of protists is likely in jeopardy, just like most reefal, benthic, and planktic metazoans. An urgent need to understand the role of protists in modern threatened oceans should be addressed soon.

scholarly journals Allosorex stenodus Fejfar, 1966 (Eulipotyphla, Soricidae): re-description of type material and re-interpretation of its fossil record

2020 ◽  
Vol 76 (1) ◽  
pp. 84-98
Author(s):  
Oldřich Fejfar ◽  
Wighart v. Koenigswald ◽  
Martin Sabol
Keyword(s):  
Fossil Record ◽  
Critical Evaluation ◽  
Morphological Characters ◽  
Microstructure Analysis ◽  
Karst Area ◽  
Eastern Asia ◽  
Enamel Microstructure ◽  
Fossil Remains ◽  
Karst Areas ◽  
Taxonomical Status

The original fossil record of Allosorex stenodus Fejfar, 1966 from Ivanovce (late Ruscinian, MN 15b) is redescribed and supplemented by the description of so far unpublished fossil remains, including upper dentition (P4 and M3) and a humerus fragment as well as the enamel microstructure analysis of m2. Based on the critical evaluation of other fossil remains from sites in Romania, Hungary, and France, the Ivanovce fossils are so far the only unquestionable recorded finds of A. stenodus in Europe, which can be considered as a local early Pliocene (MN 15) endemic species. Its occurrence is connected with the forested karst area along a broad valley of “pre-Váh” River, ecologically and climatically resembling the environment of modern karst areas in south-eastern Asia. Based on enamel microstructure analysis and unique mandible and dentition morphological characters, a separate taxonomical status of the species is also discussed.

scholarly journals Completeness metrics and the quality of the sauropodomorph fossil record through geological and historical time

Paleobiology ◽  
2010 ◽  
Vol 36 (2) ◽  
pp. 283-302 ◽  
Author(s):  
Philip D. Mannion ◽  
Paul Upchurch
Keyword(s):  
Sea Level ◽  
Fossil Record ◽  
Quantitative Methods ◽  
Phylogenetic Analyses ◽  
Type Specimen ◽  
Time Interval ◽  
Historical Time ◽  
Rock Outcrop ◽  
Type Specimens ◽  
Fossil Remains

Despite increasing concerns about the effect of sampling biases on our reading of the fossil record, few studies have considered the completeness of the fossil remains themselves, and those that have tend to apply non-quantitative measures of preservation quality. Here we outline two new types of metric for quantifying the completeness of the fossil remains of taxa through time, using sauropodomorph dinosaurs as a case study. The “Skeletal Completeness Metric” divides the skeleton up into percentages based on the amount of bone for each region, whereas the “Character Completeness Metric” is based on the number of characters that can be scored for each skeletal element in phylogenetic analyses. For both metrics we calculated the completeness of the most complete individual and of the type specimen. We also calculated how well the taxon as a whole is known from its remains. We then plotted these results against both geological and historical time, and compared curves of the former with fluctuations in sauropodomorph diversity, sea level, and sedimentary rock outcrop area. Completeness through the Mesozoic shows a number of peaks and troughs; the Early Jurassic (Hettangian–Sinemurian) is the interval with highest completeness, whereas the mid-to-Late Cretaceous has completeness levels that are consistently lower than the rest of the Mesozoic. Completeness shows no relationship to rock outcrop area, but it is negatively correlated with sea level during the Jurassic–Early Cretaceous and correlated with diversity in the Cretaceous. Completeness of sauropodomorph type specimens has improved from 1830 to the present, supporting the conclusions of other recent studies. However, when this time interval is partitioned, we find no trend for an increase in completeness from the 1990s onward. Moreover, the 2000s represent one of the poorest decades in terms of average type specimen completeness. These results highlight the need for quantitative methods when assessing fossil record quality through geological time or when drawing conclusions about historical trends in the completeness of taxa. The new metrics may also prove useful as sampling proxies in diversity studies.

scholarly journals Diversity-dependence brings molecular phylogenies closer to agreement with the fossil record

2011 ◽  
Vol 279 (1732) ◽  
pp. 1300-1309 ◽  
Author(s):  
Rampal S. Etienne ◽  
Bart Haegeman ◽  
Tanja Stadler ◽  
Tracy Aze ◽  
Paul N. Pearson ◽  
...  
Keyword(s):  
Standard Model ◽  
Fossil Record ◽  
Evolutionary Dynamics ◽  
Planktonic Foraminifera ◽  
Fossil Evidence ◽  
Rate Of Increase ◽  
The Standard Model ◽  
Molecular Phylogenies ◽  
Biological Realism

The branching times of molecular phylogenies allow us to infer speciation and extinction dynamics even when fossils are absent. Troublingly, phylogenetic approaches usually return estimates of zero extinction, conflicting with fossil evidence. Phylogenies and fossils do agree, however, that there are often limits to diversity. Here, we present a general approach to evaluate the likelihood of a phylogeny under a model that accommodates diversity-dependence and extinction. We find, by likelihood maximization, that extinction is estimated most precisely if the rate of increase in the number of lineages in the phylogeny saturates towards the present or first decreases and then increases. We demonstrate the utility and limits of our approach by applying it to the phylogenies for two cases where a fossil record exists (Cetacea and Cenozoic macroperforate planktonic foraminifera) and to three radiations lacking fossil evidence ( Dendroica , Plethodon and Heliconius ). We propose that the diversity-dependence model with extinction be used as the standard model for macro-evolutionary dynamics because of its biological realism and flexibility.

scholarly journals A fresh look at the fossil evidence for early Archaean cellular life

2006 ◽  
Vol 361 (1470) ◽  
pp. 887-902 ◽  
Author(s):  
Martin Brasier ◽  
Nicola McLoughlin ◽  
Owen Green ◽  
David Wacey
Keyword(s):  
Critical Analysis ◽  
Fossil Record ◽  
Volcanic Glass ◽  
New Approach ◽  
Microbial Origin ◽  
Cellular Life ◽  
Fossil Evidence ◽  
Rock Record ◽  
Inclusion Trails ◽  
Self Organizing

The rock record provides us with unique evidence for testing models as to when and where cellular life first appeared on Earth. Its study, however, requires caution. The biogenicity of stromatolites and ‘microfossils’ older than 3.0 Gyr should not be accepted without critical analysis of morphospace and context, using multiple modern techniques, plus rejection of alternative non-biological (null) hypotheses. The previous view that the co-occurrence of biology-like morphology and carbonaceous chemistry in ancient, microfossil-like objects is a presumptive indicator of biogenicity is not enough. As with the famous Martian microfossils, we need to ask not ‘what do these structures remind us of?’, but ‘what are these structures?’ Earth's oldest putative ‘microfossil’ assemblages within 3.4–3.5 Gyr carbonaceous cherts, such as the Apex Chert, are likewise self-organizing structures that do not pass tests for biogenicity. There is a preservational paradox in the fossil record prior to ca 2.7 Gyr: suitable rocks (e.g. isotopically light carbonaceous cherts) are widely present, but signals of life are enigmatic and hard to decipher. One new approach includes detailed mapping of well-preserved sandstone grains in the ca 3.4 Gyr Strelley Pool Chert. These can contain endolithic microtubes showing syngenicity, grain selectivity and several levels of geochemical processing. Preliminary studies invite comparison with a class of ambient inclusion trails of putative microbial origin and with the activities of modern anaerobic proteobacteria and volcanic glass euendoliths.

The early Mesozoic radiation of dinoflagellates

Paleobiology ◽  
1996 ◽  
Vol 22 (3) ◽  
pp. 329-338 ◽  
Author(s):  
R. A. Fensome ◽  
R. A. MacRae ◽  
J. M. Moldowan ◽  
F. J. R. Taylor ◽  
G. L. Williams
Keyword(s):  
Detailed Analysis ◽  
Fossil Record ◽  
The Past ◽  
Early Mesozoic ◽  
Fossil Evidence ◽  
Evolutionary Radiation ◽  
Molecular Phylogenetic ◽  
Sudden Appearance ◽  
New Evidence

Dinoflagellates are a major component of the marine microplankton and, from fossil evidence, appear to have been so for the past 200 million years. In contrast, the pre-Triassic record contains only equivocal occurrences of dinoflagellates, despite the fact that comparative ultrastructural and molecular phylogenetic evidence indicates a Precambrian origin for the lineage. Thus, it has often been assumed that the dearth of Paleozoic fossil dinoflagellates was due to a lack of preservation or recognition and that the relatively sudden appearance of dinoflagellates in the Mesozoic is an artifact of the record. However, new evidence from a detailed analysis of the fossil record and from the biogeochemical record indicates that dinoflagellates did indeed undergo a major evolutionary radiation in the early Mesozoic.

The causes of extinction

1989 ◽  
Vol 325 (1228) ◽  
pp. 241-252 ◽  
Keyword(s):  
Fossil Record ◽  
Species Turnover ◽  
Rapid Evolution ◽  
Taxonomic Diversity ◽  
Species Selection ◽  
Biotic Factors ◽  
Taxonomic Distribution ◽  
Interacting Species ◽  
Fossil Evidence ◽  
Different Types

A species may go extinct either because it is unable to evolve rapidly enough to meet changing circumstances, or because its niche disappears and no capacity for rapid evolution could have saved it. Although recent extinctions can usually be interpreted as resulting from niche disappearance, the taxonomic distribution of parthenogens suggests that inability to evolve may also be important. A second distinction is between physical and biotic causes of extinction. Fossil evidence for constant taxonomic diversity, combined with species turnover, implies that biotic factors have been important. A similar conclusion emerges from studies of recent introductions of predators, competitors and parasites into new areas. The term ‘species selection’ should be confined to cases in which the outcome of selection is determined by properties of the population as a whole, rather than of individuals. The process has been of only trivial importance in producing complex adaptations, but of major importance in determining the distribution of different types of organisms. An adequate interpretation of the fossil record requires a theory of the coevolution of many interacting species. Such a theory is at present lacking, but various approaches to it are discussed.

scholarly journals Diversification dynamics of total-, stem-, and crown-groups are compatible with molecular clock estimates of divergence times

2021 ◽  
Vol 7 (24) ◽  
pp. eabf2257
Author(s):  
Alan J. S. Beavan ◽  
Davide Pisani ◽  
Philip C. J. Donoghue
Keyword(s):  
Time Scales ◽  
Molecular Clock ◽  
Fossil Record ◽  
Divergence Times ◽  
Evolutionary Time ◽  
Crown Group ◽  
Total Group ◽  
Fossil Evidence ◽  
Evolutionary Radiations ◽  
Birth Death

Molecular evolutionary time scales are expected to predate the fossil evidence, but, particularly for major evolutionary radiations, they can imply extremely protracted stem lineages predating the origin of living clades, leading to claims of systematic overestimation of divergence times. We use macroevolutionary birth-death models to describe the range of total-group and crown-group ages expected under constant rates of speciation and extinction. We extend current predictions on origination times for crown- and total-groups, and extinction of stem-groups, demonstrating that there is broad variance in these predictions. Under constant rates of speciation and extinction, we show that the distribution of expected arthropod total-group ages is consistent with molecular clock estimates. The fossil record cannot be read literally, and our results preclude attempts to interpret the antiquity of clades based on the co-occurrence of stem- and crown-representatives.

Plate Tectonics and Evolution

2002 ◽  
Vol 11 ◽  
pp. 227-236
Author(s):  
David I. Jablonski
Keyword(s):  
20Th Century ◽  
Fossil Record ◽  
Plate Tectonics ◽  
Earth’S Crust ◽  
Fossil Evidence ◽  
Similarities And Differences ◽  
Earth's Crust ◽  
Scientific Achievements

The realization that the continents are mobile and not fixed in position, and the discovery of the processes driving that mobility, is one of the great scientific achievements of the 20th Century. From the outset, fossil evidence has been important in reconstructing past continental positions, usually by providing data on ancient similarities and differences that appear at odds with present-day geographies. However, the fossil record does much more than provide evidence on ancient continental positions: it also shows the diverse evolutionary effects that the dynamics of the Earth's crust have had on the passengers inhabiting those mobile continents.

scholarly journals The evolution of methods for establishing evolutionary timescales

2016 ◽  
Vol 371 (1699) ◽  
pp. 20160020 ◽  
Author(s):  
Philip C. J. Donoghue ◽  
Ziheng Yang
Keyword(s):  
Fossil Record ◽  
Environmental Influence ◽  
Molecular Dating ◽  
Divergence Times ◽  
Fossil Species ◽  
Time Estimates ◽  
Fossil Evidence ◽  
Probability Densities ◽  
History Of ◽  
Lineage Divergence

The fossil record is well known to be incomplete. Read literally, it provides a distorted view of the history of species divergence and extinction, because different species have different propensities to fossilize, the amount of rock fluctuates over geological timescales, as does the nature of the environments that it preserves. Even so, patterns in the fossil evidence allow us to assess the incompleteness of the fossil record. While the molecular clock can be used to extend the time estimates from fossil species to lineages not represented in the fossil record, fossils are the only source of information concerning absolute (geological) times in molecular dating analysis. We review different ways of incorporating fossil evidence in modern clock dating analyses, including node-calibrations where lineage divergence times are constrained using probability densities and tip-calibrations where fossil species at the tips of the tree are assigned dates from dated rock strata. While node-calibrations are often constructed by a crude assessment of the fossil evidence and thus involves arbitrariness, tip-calibrations may be too sensitive to the prior on divergence times or the branching process and influenced unduly affected by well-known problems of morphological character evolution, such as environmental influence on morphological phenotypes, correlation among traits, and convergent evolution in disparate species. We discuss the utility of time information from fossils in phylogeny estimation and the search for ancestors in the fossil record. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’.

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