Benton M.J. Introduction to paleobiology and the fossil record

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98 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

can exist for tens or even hundreds of millions

of years (Sheehan 2001).

Despite the fantastic potential to test models

for community change through time there

have been relatively few rigorous attempts.

Some paleontologists have recognized a

pattern of coordinated turnover followed by

stasis in which many species disappear over a

short time interval and are replaced by other

functionally and taxonomically similar species.

The new assemblages may retain their struc-

ture for 2–8 million years (Brett et al. 1996),

although in some cases this appears to occur

through repeated reassembly following dis-

turbances. By contrast Ordovician marine

assemblages from the Appalachians (see p.

38) show a strong relationship between envi-

ronmental ﬂ uctuations and uncoordinated

changes in the composition and dominance of

animals in their assemblages. Even life at a

small scale shows these patterns. An Ordovi-

cian hardground paleocommunity constructed

by encrusters, mainly bryozoans and edrioast-

eroids, on cobbles shows ﬁ rst a low-diversity

pioneer community, then a high-diversity

association, and ﬁ nally a monospeciﬁ c assem-

blage characterized by a late successional

dominant (Wilson 1985). Environmental dis-

turbances, such as the tipping over of the

cobbles, allowed a recolonization of the

hardground, thus maintaining high diversity

within the paleocommunity. Clearly in some

cases an Eltonian model may be applicable

and in others Gleasonian paradigms rule.

Evolutionary paleoecology

Biodiversity trends through time for the

majority of animal and plant groups have

been documented in some accuracy and detail

since the late 1970s (see p. 534). However, it

is clear that there are a series of ecological

changes underpinning this incredible taxo-

nomic diversiﬁ cation and such changes were

probably decoupled from each other. For

example, there have been marked changes in

the use of ecospace through the evolution of

new adaptive strategies (Bambachian mega-

guilds), an escalation in the number of guilds

and accelerated tiering both above and below

Box 4.4 Chemosynthetic environments

Amazing new discoveries in the modern oceans have revealed some of the most bizarre living crea-

tures that survive in the dark, cold depths, clinging onto the life support provided by hydrocarbon

seeps and hydrothermal vents. Uniquely, these bizarre organisms never see the light, and their food

chains are not based on sunlight and carbon, but on sulfur from hydrothermal vents. The search is

on to ﬁ nd their fossil counterparts. Kathleen Campbell, together with a range of colleagues, has been

exploring the distribution of these types of weird communities through time (Campbell 2006). She

has identiﬁ ed 40 fossil examples, recognized on the basis of key types of faunas, speciﬁ c biomarkers

and their geochemical and tectonic settings. Such communities associated with Precambrian vents

were populated by microbes and it was not really until the Silurian that we ﬁ nd our ﬁ rst groups of

metazoan chemosynthetic organisms. These organisms are strange. Gigantic non-articulated brachio-

pods are associated with large bivalves and worm tubes in a massive volcanic sulﬁ de in the Ural

Mountains (Fig. 4.19). In general terms, pre-Jurassic vent faunas were dominated by extinct groups

of brachiopods, monoplacophorans, bivalves and gastropods, and post-Jurassic faunas were popu-

lated by extant families of bivalves and gastropods. The modern vent-seep fauna is endemic and may

either have evolved from a collection of Paleozoic and Mesozoic relics or perhaps some invertebrate

groups periodically migrated into the gloom during the Phanerozoic to set up their own communi-

ties. Although unusual, the chemosynthetic world was yet another ecosystem with its own set of

rules and evolutionary paradigms, contributing to the past and present biodiversity of our planet.

Perhaps, also, during times of major and rapid environmental change, this ecosystem provided a

stable refugia where at least some organisms could escape ﬂ uctuations in those other ecosystems that

rely on light and organic nutrients.

PALEOECOLOGY AND PALEOCLIMATES 99

the substrate. Through time animals and

plants have developed innovative ways to

exist in new habitats. The exciting, relatively

new ﬁ eld of evolutionary paleoecology seeks

to tackle some large-scale ecological patterns

and trends through geological time. Why, for

example, were Cambrian food chains so short,

with few guilds, and why were tiering

levels both above and below the sediment

so restricted? In marine environments,

(a)

(c)

(e)

(d)

(b)

Figure 4.19 Selection of fossils from ancient hydrothermal vent sites. All specimens are pyritized

and are contained within a matrix of sulﬁ de minerals. (a) Gastropod: Francisciconcha

maslennikovi from the Lower Jurassic Figueroa sulﬁ de deposit, California. (b) Small worm tubes

from the Upper Cretaceous Memi sulﬁ de deposit, Cyprus. (c) Bivalve: Sibaya ivanovi from the

Middle Devonian Sibay sulﬁ de deposit, Russia. (d, e) From the Lower Silurian Yaman Kasy

sulﬁ de deposit, Russia: (d) monoplacophoran, Themoconus shadlunae and (e) vestimentiferan

worm tube, Yamankasia rifeia. Scale bars: 5 mm (a, b), 20 mm (c–e). (Courtesy of Crispin Little.)

100 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Sepkoski’s (1981) robust division of Phanero-

zoic life into his Cambrian (trilobites,

non-articulated brachiopods, primitive echi-

noderms and mollusks), Paleozoic (suspen-

sion feeders such as the articulated brachiopods,

bryozoans, corals and crinoids) and the

Modern faunas (detritus feeders such as the

echinoids, gastropods and bivalves together

with crustaceans, bony ﬁ shes and sharks) has

acted as template for much paleoecological

research (see p. 538).

Communities and habitats through time

Most paleoecological studies attempt to recre-

ate the dynamism and reality of past communi-

ties from environments ranging from mountain

lakes (see p. 90) to the strange chemosynthetic

environments of the deep sea (Box 4.4). Despite

the signiﬁ cant loss of information through

taphonomic processes, realistic reconstructions

are possible, depicting the main components,

their relationships to each other and the sur-

rounding environment. During most of geo-

logical time, microbial organisms were the sole

inhabitants of Earth. The Ediacara biota

appeared at the base of the Ediacaran System,

some 630 Ma, but most members had disap-

peared by the start of the Cambrian. McKer-

row (1978) was ﬁ rst to summarize, in broad

terms, the development of communities

throughout the Phanerozoic (see also Chapter

20). These tableaux were necessarily qualita-

tive but now there are a growing number of

more quantitative approaches providing more

accurate reconstructions of community change

through time. One of the ﬁ rst seascape recon-

structions, Sir Henry de la Beche’s watercolor

of Duria antiquior (1830), depicted life in an

early Jurassic sea. It was an iconic painting but

nevertheless scientiﬁ c, illustrating, graphically,

the relationships between predators and prey

in the Modern evolutionary fauna. Today we

know much more about the range of environ-

ments that existed during the Jurassic Period.

Jurassic Park and deep-sea worlds

Jurassic environments provide a wide range of

communities and habitats showing the early

stages of development of post-Paleozoic faunas.

A selection demonstrating environments, life

modes and trophic strategies are illustrated

(Fig. 4.20). Such tableaux have been criticized

for their lack of science. They are, however,

based on real case histories and numerical data

are now available for many of these recon-

structions. For example, two spectacular depos-

its, the Newark Supergroup and the Posidonia

Shales, provide important windows on life in

continental and marine environments, respec-

tively, during the early part of the Jurassic.

Major new ﬁ nds in the Newark Supergroup

and equivalent strata in eastern North America,

have painted a vivid picture of life on Late

Triassic and Early Jurassic arid to humid land-

scapes of Laurentia swept by occasional mon-

soons. Olsen and his colleagues (1978, 1987)

have described diverse dinosaur communities

of both large and small carnivorous thero-

pods, at the top of the food chain, together

with large herbivorous sauropods and some

early armored forms. Most of the terrestrial

tetrapods are preserved in volcaniclastic

deposits, but adjacent ﬂ uviatile facies contain

crocodiles. Lake facies have preserved diverse

ﬂ oras of conifers, cycads, ferns and lycopods.

Fast-swimming holostean ﬁ shes patrolled the

lakes and abundant insects of modern aspect,

representing seven orders, populated the

forests and shores or may have swum in the

shallows together with crustaceans.

The Posidonia Shales crop out near the

village of Holzmaden in the Swabian Alps,

Germany. The shales are bituminous or tar-

like, packed with fossils, generally with echi-

noderms and vertebrates towards the base

and cephalopods at the top. Seilacher (1985)

and his colleagues showed how this rock unit

with exceptionally preserved fossils, or Lager-

stätte, was a stagnation deposit (see p. 60)

where fossils accumulated in almost com-

pletely anoxic seabed conditions, and so were

hardly damaged by decomposers. Benthos is

rare, and encrusting and recumbent brachio-

pods, bivalves, crinoids and serpulids that

could not live on the stagnant seabed attached

themselves to driftwood, ammonite shells and

other ﬂ oating or swimming organisms to

pursue a so-called psedoplanktonic life mode.

The dominant animals were nektonic ammo-

nites and coleoids together with the superbly

preserved ichthyosaurs and plesiosaurs, now

displayed in many European museums. Some

horizons are characterized by monotypic

assemblages of small taxa such as diademoid

echinoids and byssate bivalves, like Posidonia

itself. These benthic colonizations may have

PALEOECOLOGY AND PALEOCLIMATES 101

(a)

10 cm

(b)

(c)

10 cm

(d)

10 cm

(e)

10 cm

(f)

Figure 4.20 A cocktail of Jurassic environments. Early Jurassic: (a) sand, (b) muddy sand, and (c)

bituminous mud communities. Late Jurassic: (d) mud, (e) reef, and (f) lagoonal communities. (From

McKerrow 1978.)

102 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

been promoted by storms, providing fresher-

water conditions for short periods of time.

Ecological patterns and trends through time

During the last 600 myr, both animal and

plant communities expanded and diversiﬁ ed

(Box 4.5). In simple terms the number of

Bambachian megaguilds multiplied through

the Cambrian (nine megaguilds), Paleozoic

(14) and Modern (20) evolutionary faunas.

The focus in the Cambrian was on marine

animals that were either attached or mobile

with suspension- or deposit-feeding strategies,

such as the eocrinoids and trilobites. The

morphologies of individual organisms were

rather plastic as were their community com-

positions and structures. Relatively few class-

level taxa were included in each ecological

box (Fig. 4.21). By the Ordovician, however,

the number of megaguilds had expanded,

with an overall numerical dominance of sus-

pension feeders, such as the brachiopods,

bryozoans, corals and crinoids. The Paleozoic

fauna was characterized by sedentary organ-

isms. The Modern fauna, by contrast, was

dominated by deposit-feeding, essentially

mobile animals bound into a process of esca-

lation, or ever-increasing competition, and the

ﬁ rst intense arms race on the planet. The term

arms race is used by ecologists to describe

ever-intensifying interactions between preda-

tors and prey, for example.

Throughout the Phanerozoic there seems to

have been an offshore movement in marine

faunas. New communities and taxa may have

occurred in nearshore, high-energy environ-

ments ﬁ rst, before migrating into deeper

water. Thus older, more archaic groups tended

to characterize deeper-water habitats. For

example during the Ordovician radiation (see

p. 253), typical members of the Paleozoic

fauna (brachiopods, bryozoans and crinoids)

expanded and migrated into deeper-water

habitats, while their place in shallow water

was taken by components of the Modern

fauna (bivalves and gastropods). But why?

Are nearshore habitats particularly harsh,

driving innovative communities and taxa into

deep water, or can innovative organisms arise

at any depth and those in shallower-water

environments are just more resistant to extinc-

tion and can readily migrate into deeper water

(Jablonski & Bottjer 1990)? Perhaps it was a

combination of both.

In marine environments acceleration of the

height, complexity and stratiﬁ cation of benthic

tiering was later matched by increases in the

depth and sophistication of infaunal tiering

as, particularly in Mesozoic and Cenozoic

faunas, many more organisms adopted bur-

rowing lifestyles and the benthos switched

from ﬁ lter to deposit feeding with signiﬁ cantly

more predators. The Cambrian evolutionary

fauna occupied, more or less, only the surface

of the seabed, but by the Ordovician crinoids

had developed tiers over a meter above the

seabed and burrowing had already com-

menced into the sediment. Terrestrial environ-

ments, initially dominated by small green

plants, various arthropods and snails, together

with diverse amphibian faunas in the Mid to

Late Paleozoic, changed signiﬁ cantly during

the Mesozoic, with the diversiﬁ cation of veg-

etation and eventually ﬂ owering plants, and

terminating, for now, in the high and elabo-

rate canopies we see today in the tropical rain

forests (see p. 505).

The Modern fauna was also characterized

by something rather special, an arms race

(Harper 2006). During the so-called Meso-

zoic marine revolution, predators, such as

bony ﬁ shes, crustaceans, marine reptiles and

starﬁ shes began to develop better and better

ways of crushing or opening shells. The

Modern world was a much more dangerous

place and in order to survive, potential prey

had to develop thicker, more elaborately

ornamented shells with smaller apertures

(Box 4.6) and devise more cunning evasive

strategies such as greater mobility or deeper

and deeper burrowing. Unfortunately expo-

sure to intense predation and a much more

bioturbated seaﬂ oor was no place for many

groups of epifaunal animals such as the bra-

chiopods, some groups of bivalves and echi-

noderms. But as prey developed more armor

and better evasive strategies, the hunters

developed better weaponry. Together this

escalation and increased tiering set the

Modern fauna quite apart from those of the

Cambrian and Paleozoic. Perhaps the whole

ecosystem functioned in a different way,

allowing biodiversity to continue to expand

way beyond the plateau of the Paleozoic

fauna (see p. 541).

Unlike biodiversity change, where we have

numbers of taxa to count and monitor, eco-

logical change is much more difﬁ cult to describe

and quantify. Since some changes are much

PALEOECOLOGY AND PALEOCLIMATES 103

Box 4.5 Occupation of ecospace through time

Life through time has increased in taxonomic diversity, but have the number of life modes also

increased? One way to investigate this is by mapping the increase in Bambachian megaguilds

(Bambach 1983) across the three great evolutionary faunas. The trend is one of not only increasing

numbers of megaguilds through time but also one of increased urbanization as more taxa are

squeezed into each category (Fig. 4.21a–c). But in order to sustain the increased membership there

must have been some ﬁ ne-tuning and splitting within the megaguilds as new guilds and niches were

developed within the Bambachian structure. Can this be tested with new data and why should the

number and importance of various life modes change through time? Richard Bambach and his col-

leagues (Bambach et al. 2007) have reported an increase from about one, in the Late Ediacaran, to

over 90 lifestyles in Recent and Neogene faunas (Fig. 4.21d). Between the Paleozoic and Neogene

faunas, there has been an increase in motility, infaunalization and predation. Thus the expansion of

predation and increased bioturbation may have forced organisms to adjust to new challenges and

participate in ever more complex ecosystems.

more signiﬁ cant than others, one way is to

establish a series of levels with key, identiﬁ able

characteristics (Droser et al. 2000). Four ranks

or paleoecological levels have been identiﬁ ed

(Table 4.1) based on, for example, the appear-

ance or disappearance of an entire ecosystem

(ﬁ rst), the appearances and disappearances of

dominant taxa (second), thickening or thin-

ning of the Bambachian megaguilds (third) or

the mere appearance or disappearance of a

community (fourth). During the Phanerozoic

ecological changes can be charted at all levels:

the appearance of the Ediacara biota was

clearly a ﬁ rst-order change, whereas the Cam-

brian explosion and the Ordovician radiation

involved changes at the second, third and

fourth levels. Recovery after the end-Permian

mass extinction event is a textbook example

involving the addition to existing Bambachian

megaguilds, when the tiering of marine faunas

really took off (Twitchett 2006). The major

mass extinction events have been ranked eco-

logically too (Box 4.7).

PALEOCLIMATES

The Greenland ice sheet is likely to be

eliminated [within 50 years] unless much

more substantial reductions in emissions

are made than those envisaged [and

changes will] probably be irreversible,

this side of a new ice age.

Koﬁ Annan, Past Secretary General of

the United Nations (2004)

Table 4.1 Hierarchical levels of ecological change and their signals.

Level Deﬁ nition Signals

First Appearance/disappearance of an

ecosystem

Initial colonization of environment

Second Structural changes within an

ecosystem

First appearance of, or changes in, ecological dominants of higher

taxa

Loss/appearance of metazoan reefs

Appearance/disappearance of Bambachian megaguilds

Third Community-type level changes

within an established

ecological structure

Appearance and/or disappearance of community types

Increase and/or decrease in tiering complexity

“Filling-in” or “thinning” within Bambachian megaguilds

Fourth Community-level changes Appearance and/or disappearance of paleocommunities

Taxonomic changes within a clade

Continued

104 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Suspension Herbivore Carnivore

Trilobita

Pelagic

EpifaunaEpifauna

Infauna

Cambrian

evolutionary

fauna

Paleozoic

evolutionary

fauna

Suspension Deposit Herbivore Carnivore

Suspension

Passive

shallow

Deep

passive

Deep

active

Shallow

active

Deposit Carnivore

Mobile

Reclining

Attached

low

Attached

erect

Mobile

Reclining

Attached

low

Attached

erect

Inarticulata

Articulata

Eocrinoidea

? Hyolitha

Graptolithina

Tentaculitoidea

Inarticulata

Bivalvia

rostroconchia

Bivalvia

Inarticulata

Bivalvia

Agnatha

Monoplacophora

Gastropoda

Ostracoda

Articulata

Edrioasteroida

Bivalvia

Inarticulata

Anthozoa

Stenolaemata

Sclerospongia

Crinoidea

Anthozoa

Stenolaemata

Demospongia

Blastoidea

Cystoidea

Hexactinellida

Articulata

Hyolitha

Anthozoa

Stelleroidea

Tentaculitoidea

Echinoidea

Gastropoda

Ostracoda

Malacostraca

Monoplacophora

Cephalopoda

Malacostraca

Stelleroidea

Trilobita

Ostracoda

Monoplacophora

Cephalopoda

Placoderm

Merostomata

Conodontophorida

Chondrichthyes

Monoplacophora

Ostracoda

Trilobita

“Polychaeta”

Trilobita

Bivalvia

Polychaeta

Bivalvia

Merostomata

Polychaeta

Conodontophorida

“Polychaeta”

Pelagic

Infauna

Suspension Deposit Herbivore Carnivore

Suspension

Passive

shallow

Deep

passive

Deep

active

Shallow

active

Deposit Carnivore

(a)

(b)

Figure 4.21 Bambachian megaguilds. A near full complement of lifestyles is present in the

Modern fauna (c), while fewer are represented in the matrices for the Cambrian (a) and Paleozoic

(b) faunas. (d) The numbers of life modes have increased consistently through time.

PALEOECOLOGY AND PALEOCLIMATES 105

Suspension

Epifauna

Mobile

Reclining

Attached

low

Attached

erect

Malacostraca

Gastropoda

Mammalia

Osteichthyes

Mammalia

Osteichthyes

Chondrichthyes

Mammalia

Reptilia

Cephalopoda

Bivalvia

Echinoidea

Gastropoda

Bivalvia

Polychaeta

Echinoidea

Bivalvia

Polychaeta

Malacostraca

Bivalvia

Polychaeta

Bivalvia

Echinoidea

Holothuroidea

Polychaeta

Bivalvia

Crinoidea

Gastropoda

Bivalvia

Stelleroidea

Anthozoa

Gastropoda

Monoplacophora

Gastropoda

Polyplacophora

Monoplacophora

Ostracoda

Echinoidea

Bivalvia

Articulata

Anthozoa

Cirripedia

Gymnolaemata

Stenolaemata

Polychaeta

Gymnolaemata

Stenolaemata

Anthozoa

Hexactineluda

Demospongia

Calcarea

Cephalopoda

Malacostraca

Echinoidea

Stelleroidea

Cephalopoda

Gastropoda

Malacostraca

Polychaeta

Pelagic

Infauna

Suspension Deposit Herbivore Carnivore

Suspension

Passive

shallow

Deep

passive

Deep

active

Shallow

active

Deposit Carnivore

(c)

Modern

evolutionary

fauna

CarnivoreHerbivore

Early Late LateE.M. Recent

Ediacaran Cambrian Ordovician Neogene

Geological time

Number of modes of life

mean α

skeletal faunas

soft-part faunas

Phanerozoic trends

100

(d)

Figure 4.21 Continued

During the last 600 million years the Earth

has oscillated at least ﬁ ve times between ice-

house and greenhouse conditions, spending

most of the time in greenhouse climates (Fig.

4.23). For much of the Precambrian the Earth

probably endured relatively cool climates.

The Earth is generally divided into ﬁ ve climate

zones: humid tropical (no winters and average

temperatures above 18°C), dry subtropical

(evaporation exceeds precipitation), warm

temperate (mild winters), cool temperate

(severe winters) and polar (no summers and

temperatures below 10°C). But can these

zones be recognized through deep time and be

106 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Box 4.6 Shell concentrations

Shell concentrations of various types can tell us a huge amount about environments of deposition

but also can act as a proxy for biological productivity through time (Kidwell & Brenchley 1994).

Moreover, it is possible that evolutionary changes in the diversity and ecology of organisms that

produce and destroy calcareous skeletons suggest that the nature of these concentrations may have

changed through the Phanerozoic. Data from marine siliciclastic rocks, silicate-based clastic sedi-

ments, of Ordovician-Silurian, Jurassic and Neogene ages show a signiﬁ cant increase in the thickness

of densely packed bioclastic concentrations, from thin-bedded brachiopod-dominated concentrations

in the Ordovician-Silurian to a mollusk-dominated record with more numerous and thicker shell

beds in the Neogene (Fig. 4.22). Jurassic shell beds vary in thickness depending on whether they

have Paleozoic or modern afﬁ nities as the main components. This suggests that the Phanerozoic

increase in shell-bed thickness was not controlled by diagenesis or by a shift in taphonomic condi-

tions on the seaﬂ oor, but rather by the evolution of biogenic clast producers, themselves – i.e. groups

with, ﬁ rstly, more durable low-organic skeletons, secondly, greater ecological success in high-energy

environments, and thirdly higher rates of carbonate production. These results indicate that (i) repro-

ductive and metabolic output has increased in benthic communities over time; and (ii) the scale of

time averaging in benthic assemblages has increased owing to greater hard-part durability of modern

groups. New data, however, suggest that brachiopods were probably just as durable as mollusks,

but their communities simply did not produce so many shells. The frequency and thickness of shell

beds through time may simply be down to the relative biological productivity of different groups of

organisms.

100% 0 100% 0 100%

Ord-Sil

(n = 85)

Jurassic

(n = 139)

Neogene

(n = 218)

% of shellbeds

Modern fauna

Paleozoic fauna

brachiopods

archaeogastropods

stenolaemate bryozoans

cephalopods

other mollusks

other epifaunal bivalves

oysters

infaunal bivalves

cheilostomes

Thickness (m)

Figure 4.22 Thicknesses of shell concentrations during the Ordovician-Silurian, Jurassic and

Neogene. Thick shell beds are a phenomenon of the Modern fauna, mainly generated by

bivalves. (From Kidwell & Brenchley 1994.)

PALEOECOLOGY AND PALEOCLIMATES 107

Box 4.7 Ecology of extinction events

We now have a massive amount of data across all the big ﬁ ve Phanerozoic extinction events,

but are taxon counts a good guide to the severity of each extinction? Probably not! There is a

strong ecological dimension to each event. George McGhee and his colleagues (2004) have

ranked the ecological severity of each event and the order of severity is in fact different from that

established from taxon counts. First, the ecological impacts of the ﬁ ve Phanerozoic biodiversity crises

were not all similar (Table 4.2). Second, ranking the ﬁ ve Phanerozoic biodiversity crises by ecological

severity shows that the taxonomic and ecological severities of the events are decoupled. Most marked

is the end-Cretaceous biodiversity crisis, the least severe in terms of taxonomic diversity loss

but ecologically the second most severe. The end-Ordovician biodiversity crisis was associated

with major global cooling produced by the end-Ordovician glaciations; it prompted a major loss of

marine life, yet the extinction failed to eliminate any key taxa or evolutionary traits, and thus was

of minimal ecological impact. The decoupled severities clearly emphasize that the ecological impor-

tance of species in an ecosystem is at least as important as species diversity in maintaining an eco-

system. Selective elimination of dominant and/or keystone taxa is a feature of the ecologically most

devastating biodiversity crises. A strategy emphasizing the preservation of taxa with high ecological

values is the key to minimizing the ecological effects of the current ongoing loss of global

biodiversity.

Table 4.2 Classiﬁ cation of the ecological impacts of a diversity crisis.

Impact category Ecological effects

Category I Existent ecosystems collapse, replaced by new ecosystems post-extinction

Category II Existent ecosystems disrupted, but recover and are not replaced post-extinction

Subcategory IIa Disruption produces permanent loss of major ecosystem components

Subcategory IIb Disruption temporary, pre-extinction ecosystem organization re-established post-

extinction in new clades

used to develop models for both short- and

long-term climate change? A range of geologi-

cal and paleontological criteria has helped

identify climatic zones through time (Fig.

4.24). Speciﬁ c sedimentary rocks such as

calcretes (soils rich in calcium carbonate)

and evaporites (evaporated salts) can help

identify dry, arid climates whereas dropstones

(stones that plummet from the bottoms of

melting icebergs into seabed sediments) and

tillites (rocks and sand left behind by an

advancing glacier) indicate polar conditions.

These criteria have formed the basis for Chris-

topher Scotese and colleagues’ reconstruction

of climates and paleogeogeography through

time (http://www.blackwellpublishing.com/

paleobiology/). Global climate change can

now be mapped through time with some

degree of conﬁ dence.

Climatic ﬂ uctuations through time

Short-term trends

Many climatic events are short term, occur-

ring within a time span of 100 kyr. Many

surface processes respond rapidly to climate

change, for example the atmosphere and

ocean surface waters can change within days

to a few years whereas the deep water of the

ocean basins and terrestrial vegetation may

take centuries to alter; the buildup of ice

sheets and associated sea-level changes,

however, occur over millennia. Changes in