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Figure 4.4 Schematic size-frequency histograms: (a) best (positively) skewed, common of countless invertebrate populaces with high infant mortality; (b) common (Gaussian) distribution, usual of steady-state or transported assemblages; (c) left (negatively) skewed, typical of high senile mortality; (d) multimodal distribution, common of populaces with seasonal spawning patterns; and (e) multimodal distribution, v decreasing amplitude, typical of populations cultivation by molting (ecdysis).

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Size of people (age units) size of individuals (age units)

Figure 4.4 Schematic size-frequency histograms: (a) best (positively) skewed, usual of plenty of invertebrate populations with high infant mortality; (b) normal (Gaussian) distribution, typical of steady-state or transported assemblages; (c) left (negatively) skewed, common of high senile mortality; (d) multimodal distribution, usual of populations with seasonal spawning patterns; and also (e) multimodal distribution, v decreasing amplitude, usual of populations cultivation by molting (ecdysis).

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Size of people (age units)

Figure 4.5 Schematic survivorship curves: form I tracks, boosting mortality with age; form II, continuous mortality through age; kind III, decreasing mortality through age.

Size of individuals (age units)

Figure 4.5 Schematic survivorship curves: kind I tracks, raising mortality v age; type II, consistent mortality with age; type III, diminish mortality v age.

where K is the moving capacity that the populace or top limit of population size, N is the actual population size, r is the intrinsic price of populace increase and t is the unit of time.

Thus, once N viewpoints K the rate of population growth slows right down and also the populace will technique a steady equilibrium. Such populaces are typical of an ext stable environments overcame by equilibrium types (K strategists). By comparison opportunistic types thrive in more adverse, unstable environments, wherein high development rates are usual (r strategists).

Habitats and also niches: addresses and also occupations

All contemporary and fossil organisms have the right to be classified in regards to their habitat, where they live

Box 4.1 The terebratulide brachiopod Dielasma native the Permian the the Tunstall Hills

The smooth terebratulide brachiopod Dielasma is common in the limestones and dolomites associated with the Permian reefs that the Sunderland area in northeast England. Is it feasible to use data from an easy length dimensions of the brachiopod shell to identify the expansion strategies of these animals? One sample mirrors a bimodal pattern saying two successive cohorts are current in the population; in its entirety the survivorship curve says increasing mortality through age, in perhaps a stable, equilibrium setting (Fig. 4.6). However this was no the only environment roughly these Permian reefs; other samples display different-shaped curves, part demonstrating high infant mortality in possibly less stable environments, whereas a population with a bell-shaped curve argues that the shells have actually been transported and also sorted before burial. A selection of datasets is accessible by complying with this link, http://www.blackwellpublishing.com/paleobiology/.

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Figure 4.6 Size-frequency histogram (a), polygon (b), cumulative frequency polygon (c) and survivorship curve (d) for a sample the 102 conjoined valves that Dielasma indigenous the Permian reef basic deposit the the Tunstall Hills, Sunderland. (From Hammer & Harper 2005.)

(their address) or with referral to your niche, their way of life (their occupation). Modern-day organisms occupy a variety of environments from the height of mountain Everest in ~ heights of practically 9 kilometres to depths of over 10 kilometres in the Marianas Trench in the Pacific Ocean. Acknowledgment of extremophiles (see p. 205), living in even an ext bizarre habitats, has significantly extended our knowledge of the environmental range of life top top Earth. A huge number of physical, chemical and biological factors may characterize an organism"s environment; unfortunately, couple of can be well-known in the fossil record.

Some the the most abundant and diverse communities inhabit the littoral zone, whereby rocky shores host some of the many varied and also extensively studied faunas. Because that example, practically 2000 separation, personal, instance organisms have actually been videotaped from a 250 mm2 quadrat on an

Approximate

Approximate

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Figure 4.7 testimonial of modern-day marine environments and also their depth ranges, in addition to the approximate positions of the main benthic zones. (Based top top Ager 1963.)

exposed wave-battered platform approximately the Scottish island of Oronsay. Unfortunately, few rocky shores have been recorded from the geology record; where they occur, often associated with paleo-islands, there room exciting and unusual biotas and also sediments (Johnson & Baarli 1999).

The bulk of fossil animals have been found in marine sediments, occupying a wide range of depths and conditions. The distribution of the naval benthos is managed principally by depth of water, oxygenation and temperature. The key depth zones and also pelagic settings are portrayed on Fig. 4.7. In addition, the photic ar is the depth of water penetrated by light; this deserve to vary follow to water purity and salinity yet in optimum conditions it can prolong down to around 100 m. Terrestrial environments are greatly governed by humidity and also temperature, and organisms inhabit a wide variety of continental environments, ranging from the Arctic tundras to the lush forests of the tropics.

Marine settings host a range of lifestyles (Fig. 4.8). The upper surface ar waters space rich in floating plankton, and also nektonic organisms swim at miscellaneous levels in the water column. In ~ the benthos - the beasts the live in or on the seabed - mobile nektoben-thos scuttle throughout the seafloor and also the solved or sessile benthos are resolved by a selection of structures. Infaunal biology live beneath the sediment-water interface, while epifauna live over it.

Members the most neighborhoods are affiliated in some type of competition for food, irradiate and space resources. For example, the stratification the tropical rain woodlands reflects vain in the top canopy for light, if vegetation adjusted for damp, darker conditions is emerged at reduced levels. Comparable stratification or tiering is a feature of most marine communities, becoming greater and an ext sophisticated v geological time (Fig. 4.9), rather like the skyscrapers in Manhattan seeking to optimize room on a densely lived in island. Low-level tiers were typically occupied through brachiopods and corals throughout the Paleozoic, if the greater tiers were occupied by crinoids. The Mesozoic and also Cenozoic faunas, however, are an ext mollus-kan-based v the lower tiers populated by epifaunal bivalves and brachiopods and the upper tiers lived in by bryozoans and also crinoids.

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Figure 4.8 choice of naval lifestyles above, at the surface, within and also at the base of the water column. (Based on Ager 1963.)

Seaweeds (brown, environment-friendly algae)

Seaweeds (brown, environment-friendly algae)

25 cm

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Giant bivalves, corals, sponges, " giant brachiopods

Most brachiopods, " bivalves, bryozoans

Figure 4.9 Epifaunal tiering of naval benthic communities; infaunal tiering tape-recorded in map fossil assemblages is disputed on p. 205. (From Copper 1988.)

25 cm

Giant bivalves, corals, sponges, " gigantic brachiopods

Most brachiopods, " bivalves, bryozoans

Figure 4.9 Epifaunal tiering of naval benthic communities; infaunal tiering tape-recorded in trace fossil assemblages is questioned on p. 205. (From Copper 1988.)

Trace fossil associations present that burrows might be arranged in one infaunal, tiered power structure (see chapter 19). Ausich and Bottjer (1982) identified three level with boosting depth indigenous the sediment-water interface: 0 come -60 mm, -60 to -120 mm and also -120 mm to -1 m. Throughout the faster Paleozoic, only the first tier was continuously occupied, the 2nd tier was inhabited from the so late Silurian and, finally, the third tier was populated in the Carboniferous. Tiering was likewise selectively affected by extinct events, and also tiers deeper than 500 mm room rare ~ the so late Cretaceous due to the fact that of predation through bony fishes.

Trophic structures: bottom or optimal of the food chain?

Food pyramids form the basis of most ecological systems, specifying the power flow through a chain of different organisms from extremely abundant primary producers come relatively couple of predators. A number of basic trophic or feeding strategies are known (Fig. 4.10). Several marine food chain (basically, that eats what) have actually been recorded including those overcame by suspension feeders such together brachiopods, bryozoans and also sponges. These fed mostly on phytoplankton and other organic detritus. Suspension feeding was particularly common in Paleozoic benthos; the Mesozoic and Cenozoic faunas were an ext dominated by detritus feeders, such together echi-noids, and food chain were normally longer and also more complex (Fig. 4.11).

It could seem fairly easy at an initial sight to reconstruct a food chain for a fossil assemblage, giving you have the right to work out who ate what. But that is less complicated said than done. One of the most spectacular fossil lake deposits, conquered by amphibians, has actually been documented from the top Carboniferous of

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Figure 4.10 Trophic groups, task of members and their life sites. 1, major producers: phytoplankton in surface ar waters with (a) cyanobacteria and (b) benthic algae. 2, Herbivores: browsing and also grazing gastropods. 3, Deposit feeders: (a) deposit-feeding gastropod and also (b) shallow infaunal bivalve. 4, Suspension feeders: (a) semi-infaunal, byssally-attached bivalve, (b) shallow infaunal bivalve, (c) crinoid, (d) epifaunal bivalve, and also (e) deep infaunal bivalve. 5, Carnivores: (a) nektonic fishes, (b) nekton-benthic fishes, (c) epifaunal gastropod, and (d) infaunal gastropod. (From Brenchley & Harper 1998.)

Figure 4.10 Trophic groups, activity of members and also their life sites. 1, primary producers: phytoplankton in surface waters through (a) cyanobacteria and (b) benthic algae. 2, Herbivores: browsing and also grazing gastropods. 3, Deposit feeders: (a) deposit-feeding gastropod and (b) shallow infaunal bivalve. 4, Suspension feeders: (a) semi-infaunal, byssally-attached bivalve, (b) shallow infaunal bivalve, (c) crinoid, (d) epifaunal bivalve, and also (e) deep infaunal bivalve. 5, Carnivores: (a) nektonic fishes, (b) nekton-benthic fishes, (c) epifaunal gastropod, and also (d) infaunal gastropod. (From Brenchley & Harper 1998.)

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zoo / phytoplankton-suspension feeders -carnivores
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Figure 4.11 Reconstructions the two different food chain communities. (a) A ar with a suspension-feeding food chain, displaying a selection of suspension feeders, collecting food in various ways (bivalves with a mucous trap or setae, bryozoans and also brachiopods v lophophores, foraminiferans through cilia, corals through tentacles, and sponges with flagellae). (b) A ar with a detritus-feeding food chain overcame by various varieties of bottom-dwelling deposit feeders and nektonic carnivores represented by a cephalopod and also placoderm. (From Copper 1988.)

Figure 4.11 Reconstructions the two various food chain communities. (a) A community with a suspension-feeding food chain, displaying a range of suspension feeders, collecting food in different ways (bivalves with a mucous catch or setae, bryozoans and brachiopods with lophophores, foraminiferans with cilia, corals v tentacles, and sponges v flagellae). (b) A ar with a detritus-feeding food chain conquered by various varieties of bottom-dwelling deposit feeders and nektonic carnivores represented by a cephalopod and also placoderm. (From Copper 1988.)

lake margin upland lake margin upland

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Figure 4.12 (a) Trophic structures in and also around a so late Carboniferous lake complex, Nyrany, Czechoslavakia. (b) Trophic structures in a so late Permian reef complex, northeast England. (a, based upon Benton 1990; b, native Hollingworth & Pettigrew 1998.)

Figure 4.12 (a) Trophic structures in and around a late Carboniferous lake complex, Nyrany, Czechoslavakia. (b) Trophic frameworks in a late Permian reef complex, northeast England. (a, based on Benton 1990; b, native Hollingworth & Pettigrew 1998.)

Czechoslovakia (Fig. 4.12a). The lake ecosystem recreated because that the citizens of the Nyrany Lake facility has three main environmental communities: an open up water and also lake association, conquered by fishes in addition to various bigger amphibians; a shallow water and also swamp/lake association through amphibians, little fishes, soil plants and also other tree debris; and finally a terrestrial-marginal association v microsaur (small, primitive) amphibians and primitive reptiles. Food chains have actually been resolved for each of these associations by careful study that the teeth (was it a herbivore v grinding teeth or a carnivore through slashing teeth?) of every beast, and also comparisons with modern relatives. Because that example, in the open-water environments fishes, such as the spiny acanthodians, fed on plankton but were themselves assaulted by the amphibians, presumably at the height of the food chain. In the associated terrestrial environments, plant material was consumed by a range of invertebrates, including insects, millipedes, spiders, snails and also worms; these detailed food and nutrients because that a variety of tiny amphibians, themselves food for bigger amphibians and also reptiles.

A great example the a maritime food web comes from the Zechstein Reef facies of north Europe, date from the late Permian

(Fig. 4.12b). The Zechstein benthos was overcame by varied associations that brachiopods, overshadowed in the higher tiers by fan- and vase-shaped bryozoans (Hollingworth & Pet-tigrew 1988). Both groups were sessile filter feeders. Stalked echinoderms were rarer and also occupied the highest tiers. Mollusks such as bivalves and also gastropods were vital deposit feeders and also grazers. One of the biggest predators was Janassa, a benthic ray, equipped with a formidable battery of teeth qualified of crushing the shells the the sedentary benthos.

Megaguilds

Assignment of biology to megaguilds offers another way to classify and understand the contents of a fossil community. Guilds are groups of functionally similar organisms occurring together in a community. Megagu-ilds are merely a range of adaptive strategies based upon a combination of life position (e.g. Shallow, active, infaunal burrower) and feeding kind (e.g. Suspension feeder). Part paleontologists have actually used the ax "guild" because that these categories; however, this were probably finer ecological departments within the so-called Bambachian megaguilds, named after the American paleontologist Richard Bambach, who an initial used the ide (Bambach 1983). Megaguilds have also become an effective tool in assessing long-term ecological readjust (see p. 105).

Controlling factors

The environmental niche that an biology is established by a huge range of limiting factors, many of which are not taped in the rock record (Fig. 4.13). Crucial limiting components for marine organisms are light, oxygen levels, temperature, salinity, depth and substrate (Pickerill & Brenchley 1991).

Light is the key energy source for main producers, therefore diatoms, dinoflagellates, coc-coliths and also cyanobacteria room dependent ~ above light and usually occupy the photic zone. Most organic productivity wake up in the peak 10-20 m of the water column. Essentially all eukaryotic organisms require oxygen for their metabolic processes, taking in oxygen by diffusion, in the instance of small-bodied organisms, or v gills or lungs in the situation of the bigger metazoans. There is a well-developed

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Figure 4.13 shoreline to container transect mirroring the relative prestige of different components on the circulation of organisms. (From Brenchley & Harper 1998.)

oxygen-depth file in the world"s seas and also oceans. Oxygen levels typically decrease down to 100-500 m, wherein the lot of oxygen took in by organic issue exceeds major oxygen production. Here in the oxygen minimum region (OMZ), the shortest oxygen values space reached. The number of plenty of organisms, such as corals, echinoderms, mollusks, polychaetes and sponges drop off significantly in the OMZ.

Levels that oxygen in marine atmospheres are necessary in determining who resides where. Aerobic (normoxic) settings have >1.0 ml L-1 concentrations of oxygen, dys-aerobic (hypoxic) atmospheres have 0.11.0 ml L-1 and anaerobic (hypoxic-anoxic) have ostracodes and small benthic forams, vice versa, hypersaline assemblages space of very low diversity with just a few bivalves, gastropods and also ostracodes.

Depth is just one of the most often quoted controls ~ above the circulation of naval organisms (Fig. 4.14). Return the direct affects that depth are concerned hydrostatic pressure, numerous other factors, both chemical and physical, are concerned depth; because that example, in basic terms, the grain size of sediment and also water temperature decreases with depth. Back hydrostatic press does not usually distort the shells and also soft organization of biology it can dramatically influence organisms through pockets that gas in your bodies, such as fishes and also nautiloids. Apart from the effects of hydrostatic pressure, depth can also control the solubility that calcium carbonate; cold water contains more dissolved carbon dioxide (CO2) offering a means to corrode carbonate. At provided depths in the world"s oceans, lead carbonate material starts to dissolve in ~ so-called compensations depths. Listed below the carbonate compensation depth (CCD) the resolution of calcium carbonate exceeds supply and at around 4-5 km calcite is no preserved. The depth is shallower for arago-nite, with the aragonite compensation depth (ACD) put at 1-2 km. Both the CCD and also ACD vary v latitude, being shallower at higher latitudes, and also both parameters have varied transparent geological time. Nevertheless, depth alone more than likely has tiny effect on biotic distribution, rather the many depth-related factors can be used to reconstruct the water depth of old marine communities.

Finally, the state of the substrate, rates of sedimentation and turbidity dramatically influence the distributions of benthic biology (Brenchley & Pickerill 1993). Biology have complex ecological requirements, part preferring a particular grain size, a certain type of organic material or they also respond to chemical signal (chemotaxic). There are also facility taphonomic feedback processes, wherein biogenic substrates together as shell pavements can type attachment sites for brand-new communities. In general terms, in ~ near-shore environments, over there is a large correlation between community distribution and also grain size. Diversity has tendency to be greatest in muddy sands, moderate in sandy muds, short in pure sands and virtually zero in soft muds. Additionally whether the sediments type soupy muds, loose sands, firmgrounds or hardgrounds will affect faunal distributions.

Paleocommunities

Paleocommunities space recurrent teams of organisms related to some specific set of environmental problems or limiting factors. Numerous of the concepts and also techniques used to naval fossil communities are based on the work of biologist such together the Danish scientist Carl Petersen, researching in the so late 1800s and also early 1900s. Petersen recognized a collection of level-bottom benthic communities about the Scandinavian coasts; the significant control on neighborhood distribution was water depth, back other factors such together the substrate were likewise influential.

Paleontologists were sluggish to embrace these insights from contemporary marine biology. There were a few pioneer research studies on Carboniferous assemblages in the 1930s, yet it was the classic work by Alfred Ziegler in the 1960s the really lugged these techniques to the attention of paleontologists. He figured out five depth-related, brachiopod-dominated areas in the reduced Silurian rocks the Wales and the Welsh borderlands (see chapter 12). These communities stretched from the intertidal region in the east to the deep shelf and continental slope in the direction of the west, equivalent perfectly the ancient paleogeography. This entirety system has been revamped and also is now much more widely recognized as the benthic assemblage zones (Fig. 4.15). These zones are identified on a wide variety of faunal and sedimentological criteria and may be subdivided, internally, ~ above the communication of, for example, substrate form and the degree of disturbance (Brett et al. 1993).

Describing fossil communities

Sometimes the simplest tasks are the hardest to do properly. For over a hundreds years, paleontologists have noted lists of varieties from certain localities, however these space not beneficial for eco-friendly work uneven the relative abundances of the different species are recorded as well. We need to know which types dominate (sometimes one types makes up an ext than 50% that the sample) and also which are rare (i.e. Less than 5% that the collection). Now it is much more common to file the absolute and relative diversity of every organism, shown graphically through frequency histograms, and based top top data acquired from heat transects, quadrats or an ext commonly now from bed-by-bed collecting or mass samples.

Counting conventions continue to be a problem. With numerous organisms the is reasonably simple to calculation how countless individuals to be actually stood for in a provided assemblage: univalved species (e.g. Gastropods) count together one, conversely, twin-valved types (e.g. Bivalves and also brachio-pods) might be assessed by including the most common valve (right or left, dorsal or ventral) to the number of articulated or conjoined shells. Animals that molt, such as ostracods and trilobites, early american organisms and those

Figure 4.15 Silurian maritime benthic assemblage zones and also identifying criteria. (From Brenchley & Harper 1998.)

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Figure 4.15 Silurian naval benthic assemblage zones and also identifying criteria. (From Brenchley & Harper 1998.)

that quickly fragment (e.g. Bryozoans) and also those through multi-element skeletons (e.g. Cri-noids and also vertebrates) call for more devoted counting techniques. These simple data space then transformed right into a an ext realistic snapshot of old communities populating previous landscapes and also seascapes, v histograms and also pie charts. Raw number data are very useful, yet these can also be converted to diversity, dominance and also evenness parameters, and also parameters because that taxonomic distinc-tiveness (Box 4.2). These with each other can offer us a rich summary of the composition and structure the the paleocommunity and allow numerical comparisons v other comparable assemblages. Such viewpoints have end up being routine in studies of invertebrate paleoecology but it is much more challenging to apply these techniques to vertebrate assemblages whereby sample sizes are typically much smaller.

Detailed analysis of paleocommunity structures has permitted recognition of a number of specific ar types. Pioneer areas are those that have actually just entered new ecospace, and they might be dominated by one or two an extremely abundant opportunistic species, in comparison to long-established and rather stable equilibrium communities where relatively high diversities of more or much less equally abundant animals are present. The ecological relationships between organisms is also crucial aspect that community breakthrough (Box 4.3).

Paleocommunity development through time

Communities undoubtedly change with time. Determinants such as environmental fluctuation, immigration and emigration that animals and plants, evolution and also extinction of species and coevolutionary alters will alter the composition and also structure the a community. Yet are the contents of neighborhoods tightly linked and thus evolve with each other or is the a rather haphazard arbitrarily process? living communities, when very first established, present initial high prices of replacement and instability, whereas later on stages are more stable with small change,

Box 4.2 eco-friendly statistics and also sampling sufficiency: room you gaining enough?

It is often an overwhelming to evaluate the adequacy that a paleoecological sample. Some authorities have argued that samples of about 300 provide a reasonably accurate census the a fossil assemblage. Commonly, investigators plot rarefaction curve (Fig. 4.16). These are produced simply by collecting samples the 10 and also identifying the variety of species in each. Because that each sample the 10 plotted along the x-axis, the cumulative number of species is plotted along the y-axis. The curve may level turn off at the point where no additional types are determined with additional collecting and this fixes the sample size that is enough to count the bulk of varieties present (Fig. 4.16).

A selection of statistics has actually been used to describe elements of fossil communities. Return the variety of species built up from an assemblage provides a rough overview to the diversity that the association, clearly in most cases the bigger the sample, the higher the diversity. Diversity actions are normally standardized against the sample size. Supremacy measures have actually high worths for areas with a few abundant elements and low worths where species are much more or less evenly represented; measures of evenness space usually the train station of dominance.

Margalef diversity = S - 1/log N

where S is the number of species, N is the number of specimens, ni is the number of the ith species, and also p, is the relative frequency that ,th species.

Many number techniques have actually been used to analysis paleocommunities and also their distributions. Phenetic techniques (see chapter 2) are based upon the examination of a similarity or street matrix

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Figure 4.16 building and construction of a rarefaction curve based on data gathered from a mid-Devonian brachiopod-dominated fauna, north France. The main varieties of brachiopod space illustrated: (a) Schizophoria, (b) Douvillina, (c) Productella, (d) Cyrtospirifer, (e) Rhipidiorhynchus, and also (f) Athyris. The curve levels turn off at around 300 specimens, suggesting this sample size is a sufficient census of the fauna. Magnification around x0.5 because that all.

Figure 4.16 building and construction of a rarefaction curve based upon data accumulated from a mid-Devonian brachiopod-dominated fauna, northern France. The main species of brachiopod are illustrated: (a) Schizophoria, (b) Douvillina, (c) Productella, (d) Cyrtospirifer, (e) Rhipidiorhynchus, and (f) Athyris. The curve levels off at about 300 specimens, arguing this sample dimension is a adequate census of the fauna. Magnification approximately x0.5 because that all.

Continued obtained from a raw data matrix of the presence or absence or numerical abundance of fossils at every site. Cluster analysis is most commonly used in environmental studies and there is a wide selection of both distance and also similarity measures, along with clustering techniques, to select from. R-mode evaluation clusters the variables, in most paleoecological researches the taxa, vice versa, Q-mode analysis clusters the cases, usually the localities or assemblages (Fig. 4.17).

See more: Does Mackerel Have Fins And Scales, Tunas And Flatfishes: Unclean

For example, late Ordovician brachiopod-dominated assemblages from southern China have actually been investigated by cluster analyses (Hammer & Harper 2005) and also fall right into a number of ecogroups. These data are easily accessible at http://www.blackwellpublishing.com/paleobiology/.