Aerial parts

Non-woody and woody (lignified) aerial axes can be preserved in situ under catastrophic event deposition such as high-discharge, low-frequency overbank flooding (e.g. the Fossil Grove, Glasgow) or tephra ash fall (e.g. Yellowstone Tertiary forests Spicer 1989). Leaf litters buried along with standing communities reflect canopy, understorey, and ground-cover contributions that range in age from weeks to several years (flowers, leaves, small branches and bark, cones, fruits and seeds) to a...

Plesiadapiformes

Plesiadapiforms were mouse- to marmot-sized arboreal animals that were among the most successful Paleocene-Eocene mammals. They were especially common and diverse in western North America, and are also known from Eurasia. Plesiadapiforms occupied an ecological niche approximating to that of Eocene rodents and euprimates. All three groups coexisted in the Eocene, but plesiadapiforms were considerably less spe-ciose and abundant then than during the Paleocene, a decline attributed to competition...

Estimating Completeness of the Fossil Record

Introduction the nature of completeness The incompleteness of the fossil record affects our view of evolution, so it is essential to understand the nature and magnitude of incompleteness and to correct for it. Any attempt to measure completeness requires a model of preservation. Longer-lived taxa are more likely to be preserved thus, a model of evolution is often implicit as well. These models may seem burdened with unrealistic assumptions, but they are no more so than taking the fossil record...

Sequence Stratigraphy and Fossils

Sequence stratigraphy is emerging as a powerful tool for understanding and predicting the structure of the stratigraphic record. Although originally developed for hydrocarbon exploration and later applied to basin analysis and facies models, sequence stratigraphy is being increasingly used to interpret the stratigraphic distribution of fossils. In addition, palaeontology is proving useful in aiding sequence stratigraphic interpretations. The effects of sequence stratigraphy on the fossil record...

References

Greenwald, K.P., Cook, C.B. and Ward, P. (1982) The structure of the chambered Nautilus siphuncle the siphuncular epithelium. Journal of Morphology 172, 5-22. Hewitt, R.A. and Westermann, G.E.G. (1987) Nautilus shell architecture. In W.B. Saunders and N.H. Landman, eds. Nautilus, pp. 435-461. Plenum, New York. Jacobs, D.K. (1990) Sutural pattern and shell stress in Baculites with implications for other cephalopod shell morphologies. Paleobiology 16, 336-348. Jacobs, D.K. (1992) The support of...

Taxonomic selectivity

Environmental disturbances that produce trait selectivity may also produce patterns of taxonomic selectivity (Fig. 2.3.9.1). Such highly selective taxonomic extinction can reduce biodiversity much more rapidly than random extinction (McKinney 1997). Taxonomic selectivity often occurs because body size, abundance, niche-breadth, Fig. 2.3.9.1 Extinction-biasing traits cause taxonomic selectivity because they are non-randomly distributed among higher taxa. Non-random geographical proximity of...

Heterochrony in fossils

Identifying heterochrony in the fossil record requires ontogenetic information about both ancestral and presumed descendant forms. Because two of the factors involved in heterochrony are usually available with fossil material, namely shape and size, it is often relatively easy to assess whether a particular species is either peramorphic or paedomorphic, or whether certain traits are peramorphic or paedomorphic. However, understanding which process or processes caused the het-erochronic effect...

Biodiversity through time patterns of increase

Indeed, it is assumed that life is more diverse today than it ever has been. This seems in some ways obvious, and yet it could also be construed as extraordinary vanity, somehow akin to the view that all of evolution was planned to lead to human beings, that somehow this instant in the vast span of time is the most important of all. However, it is evident that all living organisms, and all organisms known as fossils, derive from a single common ancestor...

Hypotheses of feeding in other early vertebrates

Although a bilaterally operating feeding apparatus is a synapomorphy of vertebrates (Purnell and Donoghue 1997), there is no evidence that any other extinct agnathans possessed an eversible feeding apparatus. Similarly, there is no evidence to support the hypothesis that the conodont apparatus is directly comparable to the oral or pharyngeal structures of ostracoderms. In fact, these structures have not been subjected to rigorous functional analysis and, apart from the conodonts, hypotheses of...

Extinction patterns

The most spectacular victims of the Late Devonian mass extinction were the reefs. Devonian reef ecosystems were the most geographically extensive that have ever occurred in Earth history, almost 10 times the areal extent of reefs in modern oceans. Tropical reef and peri-reefal ecosystems were destroyed in the Late Devonian extinction, shrinking by a factor of 5000 in areal extent from the Frasnian Stage to the Famennian. Tabulate corals and stromatoporoids (extinct sponges), major elements of...

Evolutionary significance of stasis and change

Evidence continues to accumulate for the pervasiveness Fig. 2.1.2.3 Examples of changes in single morphological characters in Metrarabdotos species. Each line tracks the changes in mean value in the putative ancestor species, and the solid circle represents the mean value in the earliest sample of the presumed descendant. (a) Diameter of proximal areola on ovicell (mm) in M. n. sp. 10 relative to M. tenue (see Fig. 2.1.2.2a). (b) Ovicell length (mm) in M. lacrymosum relative to M. n. sp. 3 (see...

The major plant groups

Coal swamps were forested ecosystems composed of five major tree groups. The growth architectures (Fig. 1.3.8.1), biologies, and ecologies of these groups were distinctively different and contributed to plant assemblages that were strongly differentiated by habitat (DiMichele and Phillips 1994). The dominant plants of the wettest parts of West-phalian coal swamps were tree lycopsids, colloquially known as giant club mosses. Lycopsid trees reached 30 m in height and over 1 m in diameter at the...

The Origin of Vertebrates

Although pre-Silurian vertebrates have been known since the late 1880s, they have generally been considered to be low in diversity and a relatively insignificant prelude to the principal radiation of the group in the Late Silurian and Devonian. Recent discoveries have demonstrated, however, that Ordovician vertebrate faunas are not only more abundant and widespread than hitherto suspected but also contain a far greater diversity of groups. Furthermore, there is now firm evidence that the fossil...

The Palaeozoic record of calcareous plankton

Metamorphic decarbonation of calcareous oozes in deep-sea trenches influences the biogeochemical carbon cycle on a geological time scale. Based on presence-absence data of the fossil record, calcareous nannoplank-ton (e.g. coccolithophorids), which form these oozes, did not evolve until the Late Triassic (Fig. 3.3.4.1a), and their role in the carbon cycle presumably began in earnest no earlier than about mid-Jurassic ( 150 Ma). Deposition of extensive cratonic limestones may have kept the...

Evolutionary dynamics escalation and the Mesozoic marine revolution

Although the rise in predation and the synchronous community restructuring and architectural changes of the Mesozoic marine revolution are generally accepted, the evolutionary dynamics of these changes are inadequately understood and their causes are debated. The Mesozoic decline of semi-infaunal, endobyssate taxa and their replacement by burrowing or epifaunal forms with antipredatory traits have been attributed to the differential extinction of species vulnerable to predation (Stanley 1977)....

Mesozoic

The Mesozoic was a key period in the history of insect pollination. It included the origins of at least three new clades of insect-pollinated seed plants (Bennettitales, Gnetales, and angiosperms) and important radiations of anthophilous insects. Insect pollination in the early to mid Mesozoic may have been restricted to the 'cycado-phytes' (cycads+Bennettitales), which were pollinated by Coleoptera (beetles). Extant Coleoptera demonstrate appropriate pollen and ovule feeding behaviour and were...

The role of adaptive breakthroughs

Many evolutionary radiations have been triggered by the origin of adaptive innovations (see Section 2.3.1). Although such an innovation is an intrinsic feature of a taxon, its role is similar to that of the three avenues to new ecospace the appearance of a new habitat, the extinction of pre-existing taxa, and the provisioning of new ecospace by another radiating taxon. These factors are not mutually exclusive a radiation that follows a major extinction or the provision of a new habitat is...

Criticisms of the maniraptoriform hypothesis of bird origins

Some critics of the maniraptoriform origin of birds (e.g. Feduccia 1996) have taken issue with the chronological gap between the oldest bird, the Late Jurassic Archaeopteryx, and the Cretaceous non-avian manirap-toriforms typically used in discussions of bird origins (e.g. Deinonychus, Velociraptor, Oviraptor). This criticism has become known as the 'temporal paradox' since it highlights the supposed inconsistency of arguing that birds evolved from creatures that lived several million years...

The distinctive character of Palaeozoic reefs

Although some Palaeozoic reefs achieved rates of accretion similar to that shown by modern coral reefs (e.g. 3-4mm year for the Permian Capitan Reef of Texas and New Mexico), both the community structure and relative contributions of inorganic and organic carbonate were often profoundly different. Palaeozoic reefs appear to have grown in the absence of photosymbiosis and, in some examples, much of the preservable biodiversity was housed within cryptic communities. Moreover, reef construction by...

Leaf physiognomy

Theoretical and experimental studies have demonstrated that leaf attributes ('leaf or foliar physiognomy'), such as size, shape, and the prevalence of features such as drip tips, vary along environmental gradients. This variation reflects an adaptive compromise between the need to capture light energy and manage heat gain and loss, and, at the same time, maximize the efficiency of gas exchange, transpiration, and photosynthesis. Quantitative analyses of modern vegetation leaf physiognomy and...

Speciation rate and the time for speciation

What constitutes rapid speciation and how should it be measured Perhaps most commonly, speciation rate (SR) is a measure of diversification, i.e. the number of species, per ancestral species, that arise within a clade per unit time where SRlog is a logarithmic estimate of speciation rate, n is the number of species in a clade, and t is the age of that clade. A related but distinct quantity of interest is how much time is required for speciation, i.e. how long does it take for reproductive...

The role of continental drift and the isolation of mammalian faunas

Much of Tertiary (and modern) mammalian diversity is related to the isolation of different founder groups of mammals on different continents, and subsequent convergent evolution of similar ecomorphological types. The most obvious example today is the separate nature of the Australian marsupials, with their own iteration of various adaptive types such as 'moles', 'anteaters', and 'wolves', etc. Later Tertiary dispersals have muted or obliterated many differences in mammalian faunas between...

Cambrian Food Webs

Food webs are descriptions of who eats whom within a community, thereby tracking energy flow through the system and, to an important degree, characterizing its ecological structure. Clearly any palaeoecological analysis would be greatly served by a detailed accounting of its food web. Nowhere is this more so than in the Early Cambrian when, following approximately three billion years of relatively simple microbially dominated ecologies, large energetic animals were suddenly thrust into the...

Autecology and functional morphology

Trilobite eyes are composed of calcite. Numerous lineages show convergent eye loss, associated with living below the photic zone. Hypertrophied (large) eyes, particularly those with wide fields of view, are associated with pelagic taxa (Fortey 1985). Size of eyes, size and number of lenses, and shape and orientation of visual surfaces are clues to modes of life. The number of lenses determined visual acuity, and the size of lenses was a factor in determining detectable light levels. Trilobites...

Directional control

It is not sufficient to swim forwards. It is also vital to control direction. In at least some ichthyosaurs, as in fishes and many whales, a dorsal fin passively stabilized the animal against rolling around its own longitudinal axis. However, most control was active. The limbs of ichthyosaurs were profoundly modified into unitary fins which acted as steering hydroplanes. These limbs no longer produced thrust, except perhaps minor swimming movements at low speeds. The shoulder and hip girdles...

Evolutionary significance

The fossil record of hydrothermal vents and cold seeps shows that communities of animals dependent on chemosynthetic bacteria have been present in the oceans at least since the early Ordovician, and that these communities lived under the same environmental conditions found at modern vent and seep sites. These ancient vent and seep communities appear to have always contained significant numbers of animals with endosymbiotic relationships. In general the Tertiary hydrothermal vent and cold seep...

Timing of phosphatization

The high fidelity of preservation of soft tissues in fossils from the Santana Formation is an indication that replacement must have preceded, or at least accompanied, microbial decay, and was therefore a very early dia-genetic event. Some of the fossilized soft tissues show morphologies which suggest that phosphatization accompanied decay. Tissues that appear to be partly decomposed occur alongside others that appear pristine (the Medusa effect Martill 1989). Decay experiments reproduced...

Explanations for patterns of diversification

Logistic and exponential models for the diversification of life could be compared directly. However, there is a slight ambiguity in attempting this since the initial phase of a logistic curve is essentially exponential. The key distinction is between equilibrium and non-equilibrium (or expansion) models. The former imply the existence of global equilibria in diversity, while expansion models assume that there is no ceiling to the diversity of life, or at least that such a ceiling has yet to be...

Distinguishing selection and sorting in hierarchical systems

Early advocates of the hierarchical expansion of Darwinism suggested that any difference in speciation and or extinction rates was evidence of species selection. Vrba and Gould (1986) criticized this view and argued that sorting (i.e. differential survival and reproduction) is crucially different from selection. Suppose, for example, that tall primroses have greater reproductive success than shorter forms. This difference might arise in any number of ways, for example (a) tall individuals (by...

Precambrian and Palaeozoic

It is generally agreed that medusoid cnidarians constituted the first metazoan plankton. Although it has been assumed that these were part of the Ediacaran faunas, there are also possible occurrences in older rocks. However, the Precambrian history of zooplankton is poorly understood. The appearance of metazoan hard parts and their subsequent Cambrian radiation were closely mirrored by diversifications and rapid rates of evolution in the plankton. The assemblage of zooplankton in the Burgess...

Euprimates

The oldest unequivocal primates appear suddenly at the beginning of the Eocene in Europe and North America. They already represent two major prosimian clades, Adapiformes and tarsiiform Omomyidae, which reflect the primary euprimate dichotomy into Strepsirrhini and Haplorhini (Fig. 1.5.4.1). Early euprimates were common mammals in Eocene assemblages. About 65 genera and 150 species of adapiforms and omomyids are currently recognized triple the number of taxa of extant prosimians. Eocene...

C Denys Introduction

Bone is found in nearly all vertebrates. It is characterized by a highly mineralized phase consisting mainly of hydroxyapatite, which gives hardness and resistance to compression forces. Bone also contains water (30 ) and organic compounds, dominantly collagen, which provide elasticity and resistance to tensional forces. The bones of all vertebrates are similar in structure and composition, allowing a common approach to their tapho-nomic study. The balance between the processes of destruction...

Saurischian trackways

During the Late Triassic and Early Jurassic saurischian radiation, the evolution of large sauropodomorphs (prosauropods and sauropods) is expressed in the track record by a progressive increase in trackway width, a shortening of average step length relative to footprint size, and a secondary reversion to quadrupedal progression (Fig. 4.1.11.1). Prosauropods occupy an intermediate morphological and evolutionary position between theropods and sauropods. This is clearly reflected in the morphology...

Biogeographical hierarchy and principal determinants

Just as the modern biosphere can be classified hierarchically, so too can fossil biotas. In this hierarchical system, three subdivisions are usually recognized realm, region, and province. Subregions, subprovinces, and lower community ranks are also identifiable, although it is not always necessary for every rank in the hierarchy to be recognized. In this context, the realm is regarded as the first-order biogeographical unit distinguished on a global scale by the presence (or absence) of...

The rise to dominance of modern land life

With the exception of moss-lichen tundra, and boreal conifer forests (taiga), most of the land surface today is dominated by flowering plants, even in lakes and in the seagrass banks of shallow seas. Numerous specializations of the reproductive (closed carpels, receptive stigma, double fertilization, faithful pollination, fruit variety and dispersal strategies) and vegetative (broadly laminate leaves, vessels in woods) organization of flowering plants distinguish their functional biology from...

Examples from the Great American Biotic Interchange

Horses were not the only component of the New World mixing of indigenous and immigrant mammals typically referred to as the 'Great American Biotic Interchange' (GABI), nor was all the movement from north to south. North American immigrants to South America included llamas, mastodons, tapirs, bears, and sabre-tooth cats, as well as horses. From the south came armadillos, opossums, and anteaters, as well as the phorusrhacid terror bird, the only large cursorial carnivore from South America to...

Introduction

Land plants encounter problems relating to water stress, uptake, and transport, and to aerial dispersal. Survival is associated with three major strategies (1) drought avoidance via opportunism and ephemeral life cycles completed under favourable conditions (2) desiccation tolerance in the vegetative state involving the capacity of cytoplasm to rehydrate and then function normally (poikilohydry) and (3) maintenance of an internally hydrated environment by biochemical and anatomical...

Circumstantial evidence and testing of hypotheses

Science is characterized by the testing of hypotheses. Those discussed here concern events and relationships in the past. Experiments can only focus on the performance of similar living organisms (or models) for analogical comparison. Recreating the past in all its details, for experimental manipulation, is obviously out of the question. The approach to hypothesis-testing most widely adopted in practice is to seek corroboration from other, independent lines of evidence the more observations...

Agnathan diversity

Many kinds of jawless fishes evolved throughout the Silurian and Devonian (Fig. 1.3.2.2). These include armoured forms with a scoop-shaped solid bony shield like the osteostracans (e.g. Cephalaspis), the naked lamprey-like anaspids (e.g. Jaymoytius), and the heavily scaled thelodonts (e.g. Thelodus). Finds from Canada indicate that some thelodonts, the Furcacaudiformes, had laterally compressed bodies with well-developed stomachs (Wilson and Caldwell 1998). Thelodonts in general had an internal...

Types and processes of bioimmuration

Different kinds of bioimmurations can be classified according to (1) the spatial and dynamic relationships between immurer (organism responsible for overgrowth), immuree (overgrown organism), and substratum and (2) prevailing taphonomic and diagenetic factors (Fig. 3.2.5.1). In the first case, it is useful to distinguish between epibiont bioimmurations, substratum bioimmurations, and bioclaustrations. Epibiont bioim-murations are usually three-component systems a substratum is encrusted by both...

Fossil evidence of terrestrialization

There are two main types of fossil evidence for terrestrial life body fossils and trace fossils direct and indirect evidence, respectively. Trace fossils include burrows and trackways in subaerial sediments, coprolites, and plant damage other evidence for terrestrial life, such as chemical fossils, could be included here. Trace fossils can provide evidence that animals were present on land, possibly what they were doing, but not necessarily what kind of animal left the traces. Body fossils give...

Life in the Archaean

When did life on Earth first appear What were primordial organisms like How and where did they live Though these are age-old philosophical and theological questions, they also have scientific significance. Clearly, Earth's history would have been different if abundant, diverse life had arisen when the crust solidified, perhaps 4.5 billion years ago, rather than halfway through geological time, at the end of the Archaean (2.5 Ga). To answer these questions empirically, palaeontolo-gical and...

The rise of modern C grasslands

Stable isotopes apparently provide a test for the hypothesis that the increase in hypsodonty in the Late Miocene is linked with the spread of grasses. This is because C3 plants (including grasses) have 813C values of about -26 o while C4 plants (which are mostly grasses) have 813C values of about -12 o. In the modern world, C4 grasses are the dominant grass at latitudes less than about 40 . Fossil teeth record the proportion of C3 C4 biomass in diets, and palaeosol carbonates record the...

Example of a deepsea community

The shallow-water deposits of epicontinental seas are widely distributed on all continents. In contrast, examples of deep-sea deposits and their fossils are restricted to tectonically active plate margins, such as Japan and western USA. In southern Japan, deep-sea fossils occur in many tectonically uplifted areas even Pleistocene deep-water deposits are known. The Morozaki fauna is a remarkably preserved deep-sea fauna from the Early Miocene Morozaki Group, central Japan it includes a variety...

Fungalanimal interactions

Fungi are also variously associated with animals in modern ecosystems, and although rare in the fossil record, such interactions have been documented. The earliest example involves what are interpreted as faecal pellets of Silurian age, composed entirely of bits of fungal hyphae (Sherwood-Pike and Gray 1985). Because the Rhynie chert also contains numerous arthropods, it is anticipated that this site will ultimately provide some of the first direct evidence of animal-fungal interactions. Other...

Diagenesis

Spontaneous release of soluble sphagnan The cross-linkages that the 5KMA residues in sphagnan form with the other polysaccharide chains in the living moss are extremely sensitive to acids, and under the mildly acidic conditions in the bog they hydrolyse spontaneously. This autocatalytic reaction releases soluble sphagnan very slowly into the bog water over a period of 2000 years or more. At the same time, the hyaline cell walls lose their distinctive morphology and porosity, and are converted...

Geological history

During the Cambrian, epibionts, like other suspension feeders, were rare (Fig. 4.2.8.1). This rarity may reflect a Fig. 4.2.8.1 Stratigraphic distribution and morphological classification of the principal taxonomic groups of encrusting animals represented in epibiont assemblages in the fossil record. Line thickness gives a very approximate indication of the importance of each group in encrusting assemblages. (From Taylor 1990.) Fig. 4.2.8.1 Stratigraphic distribution and morphological...

Heterogeneities in morphospace

Nearest Neighbour Morphospace

Morphospaces can encompass an infinity of possible morphologies (Richard Dawkins's 'museum of all shells') and computer programs can be used to generate any hypothetical morphology by user input of parameter values. Of key interest to palaeontologists, though, is the lack of homogeneity in the response of evolving organisms to the expanses of morphospace available to them. Fig. 2.2.3.2 Principal components plot of a 20-dimensional multivariate morphospace for Namurian ammonoids. The contours...

Parameter morphospace

Simple measurements such as length and width are often not sensitive to the process by which an organism constructs its form an elongated gastropod shell may result from a high spire (e.g. Turritella) or from an elongate aperture (e.g. Conus). In many groups of organisms, parameters can be found which relate to the geometry of construction of the morphology and are consequently more efficient and powerful descriptors. The classic example is Raup's (1966) model for helicoid logarithmic spiral...

Biota

The fossils occur on smooth cleaved surfaces, or they can be exposed by careful preparation. In many specimens only an impression survives. Often the colour of the fossils matches that of the surrounding rock in other cases there is a clear contrast, e.g. the worm Yunnanozoon is always grey. Details may be revealed in polarized light (Fig. 3.4.3.1). Thicker coloured material characterizes some of the arthropods, its composition usually modified by weathering. There is evidence of both...

The oldest fishes

The oldest definite fossil vertebrates are the remains of scales composed of bone-like tissues from the Late Cambrian Georgina Basin of central Queensland, Australia (Young et al. 1996). Early Ordovician fish remains from central Australia include several forms known from scales, such as Areyongia and Apedolepis (Young 1997). The first well-preserved impressions of complete jawless fish armours occur in the Middle Ordovician of Australia. Arandaspis had well-developed dorsal and ventral bony...

Disparity vs Diversity

Mass extinctions, radiations, competitive interactions, and the effects of ecological change have all been studied with reference to turnover in numbers of families, genera, and species (see Section 2.4 and references therein). The differential effects of major extinction events on groups progressively further up the taxonomic hierarchy are well documented. Species and genera may be wiped out with relative ease. However, extinguishing a family often entails knocking out tens or even hundreds of...

From organisms to life habits

In trying to bring fossil organisms to life, the comparative method remains the main guide. But it is an ambivalent one because an organism's form is the product of evolutionary history as well as a response to prevailing circumstances. The imprint of history on form is strong because of the pervasive controls on development exerted by the inherited legacy of genes. The historical signals of form, if interpreted uncritically, may prove misleading. As a banal illustration, it would not be...

Adaptive strategies of benthic organisms in marine oxygencontrolled environments

Physiological and morphological adaptations Many organisms which inhabit oxygen-depleted environments have to struggle with conditions that are far from optimal. A common strategy is to reduce the rate of metabolism and thus the uptake of oxygen. As a result, growth rates are much lower and individuals may become dwarfs. Some groups of organisms are able to switch, for limited periods of time (days to weeks), to a modified metabolic pathway (the succinate pathway) which can be maintained...

The killing bite

Killing Bite

The nature of the killing bite has puzzled palaeontologists for years. First, where was the bite best placed Abdomen Neck Throat And second, how was the actual kill made Was it by massive blood loss due to repeated bites, or by a single crushing bite (as is typical of modern big cats) Recent studies of tooth fracture frequency in felids, and a better understanding of sabre-tooth cat anatomy, have led to greater agreement concerning the killing bite. The choice of where to place the killing bite...

Decay

Decomposition is usually rapid and is only delayed in geologically short-term circumstances, such as extreme aridity and very low temperatures. Carcasses preserved by desiccation or deep freezing will begin to decay following climatic change and rehydration or thawing. However, carbonized soft parts are found as fossils. Plants are commonly found preserved in this way but animal remains can also be carbonized. Well-known examples include the Middle Cambrian Burgess Shale and deposits of similar...

Angiosperm characteristics

Angiosperms exhibit exceptional morphological diversity, particularly among their flowers, and this diversity is also manifested among plants at the magnoliid grade. Both large bisexual floral structures, consisting of numerous tepals, stamens, and carpels in a spiral arrangement (e.g. Magnoliaceae), and minute unisexual flowers consisting of just a single stamen or a single carpel (e.g. Chloranthaceae), occur among basal magno-liid angiosperms (Fig. 1.4.2.2). Unique defining characters that...

Methods

In order to assess the bending mechanical properties of stems, three fundamental parameters and their variation during ontogeny must be considered (1) the flexural stiffness (EI) quantifies the ability of a stem to resist bending forces, and can be determined on the basis of bending tests on living plants (2) structural Young's modulus (E) describes the stiffness of a stem in bending (the prefix 'structural' is used to emphasize that plant stems are inhomogeneous composite materials) and (3)...

Biodiversity through time land and sea compared

There are major differences between the patterns of diversification on land and in the sea, and the history of life in each realm may have been rather different. Today, about 85 of described species of plants and animals live on land, and the main groups (plants, arthropods, vertebrates) have reached their present great diversity in the past 450myr. Plants and animals have been evolving in the sea since at least 600 Ma, and the fossil record is dominated by marine species, which make up some 95...

Competition in Evolution

Ecological competition refers to the ability of a local population of one species to reduce the rate of expansion or the local population size of another species. This is accomplished by interference rather than by predation or parasitism. Interference can involve consumption of common resources, such as food or habitat space disturbance, such as altering substrate conditions or indirect effects, such as attracting common predators or para-sitoids (see review by Sepkoski 1996).

Ra Gastaldo Introduction

Terrestrial plants can be considered equivalent to the sessile benthos of the marine realm. As such, assemblages of fossil plants share many traits with those of marine animals, particularly in the origination of whole plant and plant-part accumulations. In dramatic contrast to most animals, however, plants do not have to die to contribute biomass to the stratigraphic record. Other differences that affect the taphonomy of plants include the absence of a crystalline skeletal organization, the...

Types of extinction selectivity

Many types of selectivity have been discussed in palaeontology. This is to be expected, given (1) the many kinds of environmental disturbances that have occurred and (2) the evolution of biotic traits so that extinction-proneness is not a static property among taxa. Extinction selectivity is the product of the complex interplay between these two factors, the extrinsic environmental disturbances that occur and the intrinsic biotic properties of species that determine their response to the...

Ac Scott Introduction

Wildfire plays an important role in many of today's ecosystems (Crutzen and Goldammer 1993) and has played an important role on Earth for over 325 million years (Scott 2000). The extinguishing of fire may lead to a build-up of fuel with the consequence that an even more intense fire may result in the future. Most fires are started by lightning strikes 8 million occur every day. Eight billion tonnes of vegetation are burned each year by natural wildfires, which happen not only in temperate...

Mechanics of a forelimb attack

The wolverine analogy, however, reveals nothing of the mechanism of the forelimb clutch strike in Deinonychus. Non-avian maniraptors and avians share a 'semilunate' carpal which creates the automatic extension and flexion of the wrist with the movement of the forearm. This motion is a rudimentary form of the modern avian flight stroke (Gauthier and Padian in Hecht et al. 1985). Many Fig. 4.1.13.1 Phylogeny of the Dinosauria, showing positions of the groups discussed, as well as some relevant...

Taphonomic context and history

Bone taphonomy has been analysed in different vertebrate assemblages and a methodology developed that can be applied to all types of vertebrates to determine the nature of bone modifications and their degree of diagenesis. Predation is the main agent of concentration for microvertebrate assemblages, and all predator categories are involved. Different sites in various contexts have been compared to provide a classification based either Fig. 3.1.8.3 Chemical composition changes of the major...

Problems and limitations of current knowledge

Globorotalia Evolution

There are many lower-level taxonomic, stratigraphic, and biogeographical hypotheses upon which palaeonto-logical studies of speciation are based, and confirming their validity has often been very difficult. The specimens being studied must indeed belong to a single lineage or set of sister lineages, and all branches of such a clade of sister taxa must be included in the study. Micropalaeontological studies in particular have not always paid sufficient attention to these taxonomic prerequisites....

Determination of producer

It is not generally possible to identify the producer of a trackway, unless the animal responsible is preserved at the end of it. As trace fossil taxa (ichnotaxa) are based solely on the trace morphology, rather than the identity of the producer, different types of arthropod can produce the same trackway ichnotaxon, while a single individual can produce many different ichnotaxa depending on behaviour (walking technique) or preservation (substrate conditions). Trackways may show preservational...

Mangroves

A Nypa-dominated mangrove (Nypa is a palm with a creeping stem) with subordinate occurrences of the mangrove family Rhizophoraceae (e.g. Ceriops) is reconstructed as the Early and Middle Eocene coastal vegetation of the former English, French, and Belgian North Sea coastlines (Fig. 1.5.3.1a,b) (Collinson 2000). Modern Nypa-dominated mangroves are common in South-East Asia (Collinson 2000). The Nypa-dominated mangrove may have been in place at low latitudes in the Late Cretaceous but during the...

Herbivory in arthropods

Most of our knowledge of herbivory in arthropods comes from coprolites, feeding marks on leaves and other plant parts, wood borings sometimes containing coprolites , and inferences based on comparisons of fossils with their living counterparts. Plant-bearing arthropod coprolites are oval to cylindrical in shape and can be as much as 1 mm long, although most are smaller. Those that have been analysed contain the remains of various plant parts e.g. leaves, stems, spores, pollen derived from a...

Major Events in the History of Life

1.1.1 Origin of Life, 3 a. lazcano 1.1.2 Exploring for a Fossil Record of Extraterrestrial Life, 8 1.1.3 Life in the Archaean, 13 r.buick 1.1.4 Late Proterozoic Biogeochemical Cycles, 22 1.2.1 Metazoan Origins and Early Evolution, 25 d.h. erwin 1.2.2 Significance of Early Shells, 31 s. conway morris 1.2.3 Cambrian Food Webs, 40 n.j. butterfield 1.2.4 The Origin of Vertebrates, 43 m.p. smith and i.j. sansom 1.3.1 Ordovician Radiation, 49 a.i. miller 1.3.2 Rise of Fishes, 52 j.a. long 1.3.3...

Sediment chemistry

Non-biomineralized tissues display a spectrum of resistance to decay see Section 3.2.1 . At one end are robust structural tissues, such as arthropod cuticles and the seed coats and woody tissues of plants, which are decay resistant and may be incorporated into the fossil record as organic remains. At the other end are decay-prone tissues, such as muscle or gut, which degrade very rapidly they are only preserved when they are replicated very rapidly in authigenic minerals. Both organic and...

Biodiversity today

Estimates of the present diversity of life range over at least an order of magnitude, from perhaps 2-3 million species at the lower end, to 30-100 million at the upper end. The lower estimates represent summaries of the number of species that have actually been documented. It is estimated May 1990 , for example, that some 1.7-1.8 million species of modern microbes, plants, and animals have been named so far by systematists, and that figure must be a minimum estimate of current biodiversity....

Ancient cold seep communities

Fossiliferous ancient cold seep sites are found in similar tectonic settings to modern cold seeps, and they occur typically within deep-water siliciclastic or hemipelagic sedimentary sequences as discrete carbonate lenses with very negative 813C values and complex internal structures. These ancient cold seep fossil assemblages, like their modern equivalents, are more numerous and generally more species-rich than ancient hydrothermal vent communities Campbell and Bottjer 1995 . The Tertiary...

Nothofagus as an example of biogeographical patterns

Deep Sea Fossil Brassospora

Biogeographical patterns are best explained by example. The distribution of the Southern Hemisphere terrestrial biota during and following the fragmentation of Gond-wana is an interesting and complex case. There are no general examples, since every taxon has a unique history. However, some organisms probably give a better than average guide to the patterns and processes involved, and the angiosperm genus Nothofagus southern beech is one of these. Nothofagus is prominent in the biogeographical...

Preservation

Soft Tissue Romualdo

Vertebrate fossils are abundant and some of the fish species occur in mass mortality events represented by bedding planes covered with myriad small fishes. Many specimens are preserved three-dimensionally and retain body cavities. The skeletons may be fully articulated, although many show geopetal collapse following decay of soft tissues. Phosphatized soft tissues occur abundantly within both vertebrates and invertebrates in the concretions at many sites around the basin. They were first noted...

Constraints imposed by bauplans

Raup's W-D-S-T morphospace Fig. 2.2.3.1 contains fields that are characteristic of particular taxonomic groups Raup 1966 . This results from a number of geometric and functional constraints bivalves and bra-chiopods need very high W to avoid the impairment of articulation that would result from prominent opposed Fig. 2.2.3.4 A two-dimensional morphospace for dichotomously branching structures, defined by the angle of the first dichotomy and the factor by which this angle changes in each...

History of tiering

Tiering is the vertical subdivision of space by organisms within a community, and the processes responsible for this organization include space, resources, and constructional constraints Ausich and Bottjer 1982 . The Phanerozoic history developed here is for suspensionfeeding communities on soft substrata, non-reef, shallow subtidal, and epicontinental environments. The tiering history represents the maximum characteristic tiering heights and depths within tier subdivisions. Clearly, not all...

New data Panderichthys Acanthostega Ichthyostega and others

Panderichthyids include Panderichthys Fig. 1.3.7.1b and Elpistostege Clack 1997 from the Frasnian of Latvia and Canada, respectively. They possess tetrapod-like dor-sally placed orbits, flattened skulls, enlarged ribs, fin distribution, and details of humeral morphology Coates 1996 . However, these apparently advanced characters are associated with primitive features such as a jointed braincase resembling the generalized sarcopterygian condition Carroll 1996 , and many key skeletal features...

Predation and feathers

Deinonychus Arm

Discoveries in China have revealed that coelurosaurian theropods were feathered Ji et al. 1998 . Protarchaeo-pteryx and Caudipteryx had elongate, symmetrical feathers on the hands and tails Ji et al. 1998 . Surprisingly, these animals appear to be more primitive than dro-maeosaurs. This implies that, primitively, dromaeosaurs also had elongate symmetrical feathers on their hands see Fig. 4.1.13.1, point 5 . An examination of the hand of Deinonychus shows that feathers would not prohibit its...

Role in taphonomy

The filamentous network of microbial mats and their abundant production of mucilage favours the trapping not only of sediment particles but also of small organisms. This leads to the capture of planktic species as well as animals dead on the water surface. The organisms are then carried down to the floor of the aquatic environ ment as the mat sinks to the bottom. If bottom conditions are anoxic, they can be fossilized. Many localities where fossil insects are well preserved in finely laminated...

Origin and earliest fossil records of hexapods

The sparse fossil record of mid-Palaeozoic hexapods, the pattern of colonization of land by Palaeozoic plant and arthropod groups, and temporal constraints on hexapod origins imposed by hypotheses of arthropod phylogeny on hexapod origins all suggest that the earliest hexapods probably appeared during the Late Silurian. Although often used as a synonym for 'Insecta', the term 'Hexa-poda' designates the more inclusive clade that consists of the Collembola springtails and Protura proturans ,...

Bryozoans as a model system

Morphology Bryozoan

Organisms that grow by budding morphologically variable but genetically homogeneous modules e.g. zooids within bryozoan colonies offer some special opportunities for the investigation of evolutionary tempo and mode. First, most characters whether metric, meristic, or coded behave as continuous variates, because zooids with different states of a character occur in varying proportions from colony to colony Cheetham 1987 . More significantly, breeding experiments with living bryozoan species have...

Origin of Primates

Whether the order Primates is restricted to extant forms and their undisputed extinct relatives Euprimates , or encompasses Plesiadapiformes as well, the origin of the group is enigmatic. The oldest euprimates appear abruptly in the fossil record in basal Eocene deposits of North America and Europe slightly later in Asia , with no clear indication of either their phylogenetic or geographical source. They seem to be part of an immigration event, also involving the ungulate orders Perissodactyla...

Inhumation burial by insects

Ants carry seeds to their nests where they may be buried in conditions suitable for germination. Special record, the Acacieae are few, and the important ant-dispersal syndrome in Australian Acacia probably evolved within the last 10 million years Murray 1986 . Seeds may be buried by dung beetles Scarabaeidae along with the dung. The oldest evidence of the scarabaeid dung-burying habit is Late Cretaceous see Collinson 1999 . Fig. 4.1.18.1 Fossil evidence for dispersal. a Devonian spore...

Results

Rhynia Gwynne Vaughanii

The growth form of a variety of woody Palaeozoic species with secondary growth has been analysed, including Diaphorodendron vasculare, Pitus dayi, Lyginopteris oldhamia, and Calamopitys sp. Speck 1994 Speck and Rowe 1994 Rowe and Speck 1998 . In the first three plants the analysis was based on disconnected per-mineralized fragments from which a hypothesized ontogenetic sequence was constructed. With this type of data termed 'general data' by Rowe and Speck 1998 it is impossible to distinguish...

Identifying fossil bacteria

Bacteria in the Phanerozoic record are usually preserved by lithification. Their original organic matter is partly or wholly replaced by minerals, such as apatite, calcite, silica, pyrite, or siderite Liebig 1998a,b . Thus, fossil bacteria can be identified by their morphology, but their simple shape means that other criteria must be used to distinguish them from similar non-bacterial structures. Characteristic features of bacteria are their size and shape, cellular division, association,...

Are morphospecies adequate

In the punctuated equilibria model, a species remains static for virtually all of its duration, typically millions of years, following the comparatively brief interval of change associated with its origin. Thus, stasis is a long-term phenomenon requiring palaeontological data for its identification. Inevitably, the question of whether biological species can be recognized in the fossil record is raised Levinton 1988 . Fossil species are morphospecies, for the most part based on preservable...

Biogeographical processes

If an organism is spatially distributed in a way that warrants explanation, there must have been dispersal events, where organisms presumably migrated across pre-existing barriers, and or vicariance events, where the formation of barriers fragmented the ranges of once continuously distributed species. These alternatives represent past events that cannot be directly observed. For each case examined, data must be gathered to test hypotheses formulated to explain current distributions. These data...

Cuticle chemistry and structure

Chitin Sclerotization

The epicuticle consists of cuticular waxes, which are composed mainly of straight chain and branched hydrocarbons, wax esters, fatty acids, alcohols, ketones, and sterols e.g. cholesterol , and function in preventing dehydration. The rest of the cuticle is composed mainly of two biopolymers, chitin and protein, which form a complex structure cross-linked by catechol, aspartic, and or histidyl moieties Briggs et al. 1998 . Chitin, a nitrogen-containing polysaccharide, provides the structural...

Pack hunting behaviour in dromaeosaurs

Fossil evidence supports the possibility of pack hunting behaviour in dromaeosaurs when they were attacking prey significantly larger than themselves. Deinonychus teeth and body fossils are frequently found associated with a single Tenontosaurus, an ornithischian two or more times the size of Deinonychus Maxwell and Ostrom 1995 . Multiple Deinonychus would have leaped at the tenontosaur and employed the forelimb attack. An analogy for the attack of a single Deinonychus during the fray is the...

Ancient hydrothermal vent communities from other tectonic settings

Fossil assemblages have been found in a number of Palaeozoic sediment-hosted sulphide and barite deposits. These are interpreted as representing low temperature hydrothermal vent sites within sedimentary systems some are possible ancient analogues of modern sedimented vent sites, like those in the Gulf of Mexico. Carboniferous examples include carbonate mounds with sulphide mineralization from Newfoundland, containing low-diversity, high-abundance faunas of brachiopods, trepostome bryozoans,...

Pelagic trilobites

There is a convincing functional morphological case that some telephinid and cyclopygid trilobites were pelagic Fortey 1985 . These planktic trilobites apparently descended to the sea floor to moult see Whittington 1992 . Flume tank experiments suggest that Parabarran-dia may have been nektonic, based on its streamlined form Fortey 1985 . Hypotheses that small or spinose trilobites were pelagic or epipelagic are usually unconvincing when functional morphology, taphonomy, and stratigraphic...

Mammaliaforms and mammals

The earliest true mammals are known from the Late Tri-assic Norian , about 210Ma. Appearing somewhat earlier are what might be called near-mammals, creatures which in life probably looked like mammals but which lie phylogenetically outside the Mammalia as currently defined the common ancestor of monotremes, marsupials, and placentals and its descendants McKenna and Bell 1997 . The near-mammals are placed in a more inclusive taxon Mammaliaformes, which includes Mammalia plus the Late Triassic...

Dissociated heterochrony

The role of peramorphosis in generating increase in body size by either hypermorphosis or acceleration suggests that Cope's Rule the trend of phylogenetic increase in body size may have its origins in peramor-phosis. Studies of lineages of Jurassic bivalves and ammonites Hallam 1975 demonstrated that almost all showed trends to increased body size. Similar patterns are evident in foraminifers, primates, and other mammals McKinney in McNamara 1990 . One consequence of peramorphosis involving...

Palynoecological fingerprints

Pollen grains are subjected to corrosion and degradation in the interval between aeolian deposition and excretion by soil organisms. During the complex cycle of consumption, excretion, and decay of organic matter by the soil fauna, pollen grains and spores are subjected to intensive mechanical damage. Soil pollen spectra are useful ecological 'fingerprints' for archaeological and landscape-ecological studies. The contrast between the pollen-producing species represented in spectra following the...

Palaeoenvironment

The Romualdo Member yields as many as 25 species of fishes, but turtles, crocodiles, pterosaurs, and dinosaurs are also present Martill 1993 . Invertebrates are less diverse but include the ostracod Pattersoncypris micropa-pilosa in superabundance, larvae of portunid crabs, small shrimp-like crustaceans, and molluscs including corbu-lid bivalves and several small gastropods . Coprolites are very common and are often rich in small fish bone inclusions. Plants include horsetails, ferns, cycads,...

Palaeoecological approaches

Palaeoecological data that are used for the reconstruction of biotic recoveries after mass extinctions include palaeocommunity and biofabric information as well as taxonomic data with an ecological component. Such data are not easily extracted from literature or museum collections and generally require new field studies. Important concepts include the following 1 Opportunists Fig. 2.3.10.1 are taxa that undergo a dramatic increase in abundance during the recovery interval Hallam and Wignall...

Multiple impacts hypothesis

Multiple impacts of asteroids or comets on the Earth have been proposed as an alternative to glaciation as a mechanism for producing pulses of global cooling McGhee 1996 . The Late Devonian does seem to have been a time of increased impact frequency, in that from 6 to 10 known terrestrial impact craters are currently thought to be of Late Devonian age. Two of these, the Siljan crater in Sweden and the Charlevoix crater in Canada, are definitely of Late Devonian age and are quite large 52 km and...

Geographical selectivity

Geographical extinction selectivity occurs because most catastrophic events, as well as more frequent background disturbances, do not influence all regions with equal magnitude. Both background and mass extinction rates vary among geographical biotas Flessa and Jablonski 1996 . Geographical selectivity may also cause taxonomic selectivity Fig. 2.3.9.1 because related species tend to be found in geographical proximity Gaston and Blackburn 1997 . Three basic categories of habitats are often...

Heterochrony and evolutionary trends

Heterochrony also plays an important role in evolutionary trends. These trends can be either anagenetic or cladogenetic, and within or between species McNamara 1990 . The relationship between evolutionary trends and heterochrony arises because, by their very definition, trends are unidirectional, in much the same way as are ontogenetic trajectories. However, for trends to develop, extrinsic factors are also critical, in addition to the intrin sic factor of heterochrony. Selection of either...