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

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498 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

conifers and ferns were adapted to drier con-

ditions, and they occupied elevated locations

such as levees, the banks of sand thrown up

along the sides of rivers. There are hints of

extensive dry upland vegetations during the

Carboniferous, but the fossil record of these

is barely preserved. Surprisingly, some of the

best preservation came about through huge

forest ﬁ res (Box 18.5).

Towards the end of the Carboniferous, the

ﬂ oodplain vegetation of Europe and North

America changed, probably as a result of

slight drying of the environment. The club-

mosses were replaced to some extent by the

dryland ferns and seed ferns. These boggy

habitats virtually disappeared in Europe and

North America by the end of the Carbonifer-

ous, but persisted to the end of the Permian

in China.

Conifers

Conifers are the most successful gymno-

sperms, having existed since the Pennsylva-

nian, and being represented today by over

550 species. Living conifers include the tallest

living organisms of all time, the Coastal

Redwood of North America, Sequoia semper-

virens, which can reach over 110 m tall and

an estimated 1500 tonnes. Conifers have a

variety of adaptations to dry conditions,

including their narrow, needle-like leaves with

thick cuticles and sunken stomata, all adapta-

tions to minimize water loss. The tough

needles also escape freezing in cold polar

winters. The seeds are contained in tough

scales grouped in spirals into cones, usually

borne at the end of branches, while the pollen-

producing cones are usually borne on the

sides of branches.

The Cordaitales of the Carboniferous and

Permian are a distinctive group of early coni-

fers which had strap-shaped, parallel-veined

leaves (Fig. 18.19). Some Cordaitales were

tree-like, and bore their leaves, sometimes up

to 1 m long, in tufts at the ends of lateral

branches. The Voltziales, of Pennsylvanian to

Jurassic age, are represented by abundant

ﬁ nds of leaves and cones. The cones show a

variety of structures, some with a single fertile

scale at the tip, showing apparent intermedi-

ate stages to the cones of modern conifers,

where all or most scales are fertile.

Modern conifers radiated in the Late Trias-

sic and Jurassic, possibly from ancestors

among the Voltziales. The main families –

Podocarpaceae (southern podocarps), Taxa-

ceae (yew), Araucariaceae (monkey puzzle),

Cupressaceae (cypresses, junipers), Taxodia-

ceae (sequoia, redwood, bald cypress), Ceph-

alotaxaceae and Pinaceae (pines, ﬁ rs, larches)

– are distinguished by leaf shape and features

of the cones. Podocarps and yews do not have

cones.

Diverse gymnosperm groups

Compared to the conifers, the other gymno-

sperm groups did not radiate so widely. The

ginkgos are represented today by one species,

Ginkgo biloba, the maidenhair tree, a native

Figure 18.17 The seed fern Glossopteris, a

4 m-tall tree, from the Late Permian of Australia.

(Based on Delevoryas 1977.)

FOSSIL PLANTS 499

Box 18.5 Reconstructing ancient plant ecology

Some of the best evidence about fossil plants is microscopic, and indeed the scanning electron micro-

scope (SEM) has revolutionized the levels of detail that paleobotanists can retrieve. In the tropics

today there are often vast wildﬁ res that burn up hundreds of acres of forest. Fires may be started

by a carelessly thrown cigarette or a bottle that focuses the rays of the sun, but usually the causes

are natural; fallen branches and leaves may just be so dry that a chance lightning strike may spark

off a huge conﬂ agration that burns for days or weeks.

Wildﬁ res are not always destructive; indeed, many plants rely on occasional ﬁ res to clear old

timber and to allow new shoots to grow. And the ash from the ﬁ re provides phosphorus and other

nutrients. Wildﬁ res were common in the past, and particularly in the tropical belt during the Car-

boniferous when atmospheric oxygen levels may have been higher. Howard Falcon-Lang of the

University of Bristol has studied this phenomenon, and he has shown the remarkable detail that may

be observed from ancient charcoal, the burned up remnants of wood. When the charcoal is examined

under an SEM, it shows distinctive subcellular pits that allow identiﬁ cation of the precise type of

tree caught in the ﬁ re (Fig. 18.18a). Fine details such tree rings are also preserved, indicating perhaps

a seasonal tropical climate like present-day East Africa (Fig. 18.18b).

Close study of the distribution of charcoal and the sedimentology of typical Carboniferous beds in

North America shows that ﬁ res were commonest in the higher areas, away from the banks of rivers,

where plant debris could become very dry (Fig. 18.18c). The wildﬁ res may have been set off by nearby

volcanic eruptions. Careful measurements through the sediments suggest that wildﬁ res may have been

very frequent in Carboniferous times. They must have been a regular part of the growth and regrowth

of forests, as well as destabilizing hill slopes thus triggering occasional landslides.

Read more about Carboniferous wildﬁ res and plant ecosystems in Falcon-Lang (2000, 2003) and

at links listed at http://www.blackwellpublishing.com/paleobiology/. Read about another astonishing

discovery in the Carboniferous, a huge rain forest in Illinois, catastrophically buried by a sudden

rise in sea level, in DiMichele et al. (2007).

(a)

(b)

Figure 18.18 Carboniferous wildﬁ res and the use of the SEM: (a) ancient charcoal can reveal

spectacular details under the SEM, such as cross-ﬁ eld pitting, which provides evidence for which

species of plants burned; and (b) part of a tree-ring. Note the transition from thin-walled “early

wood” (left) to thick-walled “late wood” (center). The rings of growth may indicate a seasonal

tropical environment like northern Australia or East Africa. Study of these plant remains and the

sediments shows that wildﬁ res happened every 3 to 35 years, and especially in drier uplands (c).

PDP, poorly-drained coastal plain; WDP, well-drained coastal plain. (Courtesy of Howard

Falcon-Lang.)

Continued

500 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

(c)

Cordaites

(burning)

Pteridosperm

Sphenopsid

Lycopsid

(buried)

Red mudstone

Gray mudstone

Sheet sandstone

Channel sandstone

Calcrete nodule

Debris flow

Upland fires lead to

slope destabilization

and debris flows

Upland cordaite-dominated

vegetation on calcrete soils

Uplands

8 km

Cumberland basin

Lowland vegetation dominated by

cordaites with minor pteridosperms,

sphenopsids, and rare lycopsids

WDP

units

PDP

units

Facies 4

Facies 3

Facies 2

Facies 1

of China, but seen today as a typical urban

tree in parts of North America and Europe.

Ginkgos were more diverse in the Mesozoic.

Leaf shape varies from the fan-shaped struc-

ture in the modern form, to deeply dissected

leaves in some Mesozoic taxa (Fig. 18.20a, b).

Catkin-like pollen organs and bulbous stalked

ovules are borne in groups on separate male

and female plants. The leaves in the modern

Ginkgo are deciduous, that is they are shed

in winter, and this may have been a feature of

ancient ginkgos.

The cycads, represented today by 305 trop-

ical and subtropical genera, are trees with a

stem that ranges in length from a small tuber

to a palm-like trunk up to 18 m tall. The

leaves are provided with deep-seated leaf

traces that partially girdle the stem. Leptocy-

cas (Fig. 18.20c) from the Late Triassic of

North Carolina has a 1.5 m-tall trunk,

showing a few traces of attachment sites of

leaves that had been lost as the plant grew,

and a set of nine or 10 long fronds near the

Figure 18.19 The early conifer Cordaites, about

25 m tall. (Based on Thomas & Spicer 1987.)

Figure 18.18 Continued

FOSSIL PLANTS 501

(a) (b)

(c)

(d)

Figure 18.20 Diverse gymnosperms: (a) leaves of

the modern ginkgo, Ginkgo biloba and (b) of

the Jurassic ginkgo, Sphenobaiera paucipartita;

Leptocycas gigas a from the Late Triassic of

North America; and (d) reconstruction of the

2 m-tall bennettitalean Cycadeoidea from the

Cretaceous of North America. (Based on

Delevoryas 1977.)

top of the trunk. Many other cycads show

marked leaf bases along the entire length of

the trunk. Cycad fronds are typically com-

posed of numerous parallel-sided leaﬂ ets

attached to a central axis in a simple frond-

like arrangement, but others had undivided

leaves.

The bennettitaleans, or cycadeoids, were a

Mesozoic group of bushy plants with frond-

like leaves very like those of cycads. Some

bennettitaleans had a trunk up to 2 m tall,

with bunches of long fronds at the top of the

trunk and on subsidiary branches. Other ben-

nettitaleans like Cycadeoidea (Fig. 18.20d)

had an irregular ball-like trunk covered in leaf

bases, representing former attachment sites of

fronds, and with a tight tuft of long feathery

fronds on top. Some bennettitaleans had

ﬂ ower-like structures (Fig. 18.21a). Classic

dinosaur scenes of Jurassic and Cretaceous

age often picture one or other of these ben-

nettitaleans in the background.

The gnetales have a patchy fossil record,

with two Late Triassic examples, a few in the

Cretaceous and Tertiary, and three living

genera. Gnetales have distinctive pollen that

is very abundant in Cretaceous sediments.

The group was probably much more diverse

at this time. Gnetales gained prominence

among botanists because the group is thought

by some to be the closest living gymnosperm

relative of angiosperms. In particular, gnetales

may have their ovules and pollen organs

in cones that are rather ﬂ ower-like

(Fig. 18.21b).

FLOWERING PLANTS

Flowers and angiosperm success

The angiosperms are by far the most successful

plants today, with over 260,000 species and

occupying most habitats on land. Most of the

food plants used by humans are angiosperms

– wheat, barley, apples, cabbage, lentils, peas,

olives, pumpkins and many more. Angio-

sperms arose during the Mesozoic, and radi-

ated dramatically during the mid-Cretaceous.

The following are important characteristics

of angiosperms:

1 The ovules are fully enclosed within

carpels (Fig. 18.21c). It is believed that

carpels are modiﬁ ed leaves that grew

502 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

around the ovules, and provided a secure

protective covering. In angiosperm devel-

opment, the carpels grow around the

ovules and fuse, although in some magno-

lias the carpels are not completely fused

when fertilization takes place.

2 Most angiosperm ovules have two integu-

ments, or protective casings.

3 Most angiosperms have pollen grains with

a double outer wall separated by columns

of tissue.

4 Angiosperms have a ﬂ ower (Fig. 18.21c),

a structure that is composed of whorls of

sepals and petals in most. The ﬂ ower

includes the carpels and stamens, the male

reproductive structures. The structure

of ﬂ owers is not standard in all

angiosperms.

5 Angiosperms all show double fertilization,

that is, two sperm nuclei are involved in

fertilization. One unites with the egg

nucleus, while the other fuses with another

nucleus that divides to form the food

supply for the developing embryo. Double

fertilization has been described also in

Gnetales.

6 Most angiosperms have water-

transporting vessels rather than just xylem

tracheids. This feature, however, is absent

in some magnolids and hamamelidids,

and is present in gnetales.

7 Most angiosperms have a net-like pattern

of veins in their leaves.

Most of these characters are regarded as

typical of angiosperms, but many are not

unique to angiosperms, nor are they present

in all angiosperms. The only one that seems

to be an acceptable apomorphy of the group

is the possession of carpels around the ovule

(character 1 above).

Flowers are certainly the most obvious

feature of angiosperms, but several gymno-

sperm groups also had organs that bear certain

resemblances to ﬂ owers. Bennettitaleans (Fig.

18.21a) and Gnetales (Fig. 18.21b) have ﬂ ower-

like structures with the ovule in the center, and

around them structures resembling petals.

The secret of the success of the angiosperms

may be the ﬂ ower and the fully enclosed

ovule. The carpels protect the ovule from

fungal infection, desiccation and the unwel-

come attentions of herbivorous insects.

Double fertilization is said to offer the advan-

tage that the parent plant does not invest

energy in creating a large food store, as in

gymnosperms (see Fig. 18.12), until fertiliza-

tion of the ovule is assured. Pollen is produced

within the anthers, which are typically borne

on long ﬁ laments arranged around the cen-

trally placed ovary or ovaries. Pollen grains

are transported, by animals, often insects, or

by the wind, to the stigma, and from it the

pollen grains send pollen tubes to the ovules

through which the sperm pass.

The petals, often brightly colored, with

special fragrances and supplies of nectar

(sugar water), are all adaptations of angio-

sperms to ensure fertilization by insects. Some

gymnosperms show hints of this pattern: the

(a)

(b)

(c)

ovulate

receptacle

bract

stigma

anther

ovary

ovule

carpel

integument

petal

microsporophyll

Figure 18.21 Evolution of the angiosperm

ﬂ ower: (a) cone of the Jurassic bennettitalean

Williamsoniella, showing the female fertile

structure, the ovule, contained in a central

receptacle, and surrounded by the male fertile

structures, the microsporophylls; (b) ﬂ ower of

the gnetale Welwitschia, showing the central

ovule, and surrounding male elements; and

the same pattern, but with the seed enclosed in

a carpel.

FOSSIL PLANTS 503

living gnetalean Welwitschia has a ﬂ ower with

“petals” (Fig. 18.21b), and it secretes a nectar-

like pollination drop as tempting food for its

insect pollinator. It is clear that the evolution

of angiosperm characters was paralleled by

the evolution of major new groups of insects

that fed from ﬂ owers and pollinated the

ﬂ owers (Box 18.6).

The ﬁ rst angiosperms

There has been heated discussion among

paleobotanists over the past century about the

oldest angiosperm fossil, and about the closest

relatives of angiosperms. The oldest generally

accepted angiosperms are Early Cretaceous in

age, but there have been repeated reports of

Jurassic and Triassic angiosperms, although

most of these have been highly controversial

(Friis et al. 2006). Indeed, such older angio-

sperms might be expected if angiosperms are

truly the sister group of gymnosperms, as

current molecular phylogenies imply (Frohlich

& Chase 2007) (see Fig. 18.4): this

tree implies that angiosperms must be as

old as gymnosperms, dating back to the

Carboniferous.

The oldest ﬂ owers are Early Cretaceous in

age, and fossils have been reported from

North America, Europe and Asia. Most spec-

tacular, and probably oldest, is Archaefructus

from the Liaoning Formation of China (see p.

463). This fossil, named in 2002, was billed

as either the ﬁ rst angiosperm, or the closest

sister group of Angiospermae. Some of the

rare and remarkable fossils of the earliest

angiosperms show soft parts of ﬂ owers, such

as sets of ﬂ eshy stamens with pollen grains

inside, and evidence of ﬁ ve-fold symmetry of

the ﬂ ower parts, typical of modern angio-

sperms (Friis et al. 2006). Even more spec-

tacular fossil specimens of ﬂ owers are known

from the beginning of the Tertiary, where

specimens are preserved in lithographic lime-

stones, in chert and in amber (Fig. 18.23).

Other more commonly preserved fossil evi-

dence for the ﬁ rst angiosperms consists of

pollen, leaves, fruits and wood.

Radiation of the angiosperms

Angiosperms radiated to a diversity of 35

families by the end of the Cretaceous (Fig.

18.24). The success of the angiosperms in the

mid-Cretaceous may have been driven by

environmental stresses. The early angiosperms

lived in disturbed ephemeral habitats, such as

riverbeds and coastal areas, and they were

opportunists that could spread quickly when

conditions were right. In addition, the special-

ized reproductive systems of angiosperms

perhaps promoted rapid speciation, especially

in terms of the increasing matching of ﬂ ower

and pollinator.

There are two competing hypotheses for

angiosperm origins: the paleoherb hypothesis

suggests that the basal lineages were small

plants (herbs) with rapid life cycles, while the

magnoliid hypothesis suggests that the basal

lineages were small trees with simple ﬂ owers

and slower life cycles. Older phylogenetic

analyses tended to show magnolias and

laurels as the basal-most angiosperms, and

this seemed to suggest that ﬂ owers were not

such a key innovation as had been

assumed.

The paleoherb hypothesis is now conﬁ rmed

by most large-scale molecular and morpho-

logical phylogenies of angiosperms (e.g. Soltis

& Soltis 2004; Haston et al. 2007). These

have identiﬁ ed the most basal living angio-

sperm as Amborella, a rare understory shrub

that is found in cloud forests of New Caledo-

nia. Amborella has spirally arranged ﬂ oral

organs and other apparently primitive fea-

tures. Close to the base of the angiosperm tree

are an array of paleoherbs, low plants such as

the Nymphaeaceae (water lilies), monocots

(gingers, grasses, palms and relatives) and

Piperales (peppers and relatives). Next in

the tree come the Laurales (laurels and

relatives) and Magnoliales (magnolias and

relatives).

The classic division of angiosperms into

monocots and dicots does not now work so

clearly because “dicots” are paraphyletic in

the new phylogenies. The monocots form a

clade, and they have one cotyledon (food-

storage area of the seed), the ﬂ ower parts

arranged in threes and parallel leaf-venation

patterns. The “dicots” – all other ﬂ owering

plants – have two cotyledons, ﬂ ower parts

often in fours and ﬁ ves, net-like venation pat-

terns on the leaves, and specialized features of

the vascular tissues in the wood. These two

groups are readily distinguishable in the Cre-

taceous. During the Tertiary, more and more of

the modern families appeared, so that at least

Box 18.6 A new career for insects: pollination

Pollinating insects existed before the Cretaceous and the radiation of the angiosperms, but their role

was minor, feeding at the ﬂ owers of some of the advanced gymnosperms. During the Cretaceous,

however, there is striking evidence for angiosperm–insect coevolution (Fig. 18.22). Groups of beetles

and ﬂ ies that pollinate various plants were already present in the Jurassic and Early Cretaceous, but

the hugely successful butterﬂ ies, moths, bees and wasps are known as fossils only from the Creta-

ceous and Tertiary.

The composition of insect faunas changed during the Cretaceous and Tertiary. One group to

evolve substantially at that time was the Hymenoptera – bees and wasps. The ﬁ rst hymenopterans

to appear in the fossil record, the sawﬂ ies (Xyelidae), had been present since the Triassic. Some fossil

specimens have masses of pollen grains in their guts, a clear indication of their preferred diet. The

sphecid wasps that arose during the Early Cretaceous had specialized hairs and leg joints that show

they collected pollen. Other wasps, the Vespoidea, and the true bees appear to have arisen in the

Late Cretaceous.

The ﬁ rst angiosperms may not have had specialized relationships with particular insects, and may

have been pollinated by several species. More selective plant–insect relationships probably grew up

during the Late Cretaceous with the origin of vespoid wasps that today pollinate small radially sym-

metric ﬂ owers. These kinds of specialized relationships are shown by increasing adaptation of ﬂ owers

to their pollinator in terms of ﬂ ower shape, and the food rewards offered, and of the pollinator to

the ﬂ ower. Late Cretaceous angiosperms similar to roses had specialized features that catered for

pollinators that fed on nectar as well as pollen.

Read more on web sites listed at http://www.blackwellpublishing.com/paleobiology/.

Coleoptera

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) (m)(n) (o) (p) (q)

Early Late Cretaceous

Early

Tertiary

Eocene

Paleocene

Maastrichtian

Campanian

Santonian

Coniacian

Turonian

Cenomanian

Albian

Aptian

Barremian

Hymenoptera

Lepidoptera

Diptera

Figure 18.22 The coevolution of ﬂ oral structures and of pollinating insects during the entire span

of the Cretaceous and the early part of the Tertiary. Some of the major ﬂ oral types are (a) small

simple ﬂ owers, (b) ﬂ owers with numerous parts, (c) small unisexual ﬂ owers, (d) ﬂ owers with

parts arranged in whorls of ﬁ ve, (e) ﬂ owers with petals, sepals and stamens inserted above the

ovary, (f) ﬂ owers with fused petals, (g) bilaterally symmetric ﬂ owers, (h) brush-type ﬂ owers, and

(i) deep funnel-shaped ﬂ owers. Pollinating insects include (j) beetles, (k) ﬂ ies, (l) moths and

butterﬂ ies, and (m–q) various groups of wasps and bees: (m) Symphyta, (n) Sphecidae,

(o) Vespoidea, (p) Meliponinae, and (q) Anthophoridae. (Based on information in Friis et al. 1987.)

FOSSIL PLANTS 505

250 of the 400 or so extant families of angio-

sperms have a fossil record of some kind.

Angiosperms and climate

Angiosperms are highly sensitive indicators of

paleoclimates on land, and they provide the

best tool at present for estimating tempera-

tures, rainfall patterns and measures of sea-

sonality. The key to the use of angiosperms in

this way is the fact that so many modern taxa

may be traced well back into the Tertiary and

Cretaceous, and paleobotanists assume that

adaptations that are observed today had the

same functions in the past.

Studies on North American Late Creta-

ceous angiosperm leaves have shown how

precise these climatic estimates may be.

Upchurch and Wolfe (1987) established ways

of assessing temperatures and rainfall mea-

sures from key leaf features, such as:

1 Leaf size: largest leaves are found in tropi-

cal rain forest, and size diminishes as tem-

perature and moisture decline.

2 Leaf margins: in tropical areas, most

angiosperm leaves have entire (unbroken)

margins, whereas in temperate areas there

are many more tooth-margined leaves.

3 Drip tips: leaves from tropical rain

forest species have elongated tips to allow

water to clear the leaf during major

downpours.

4 Deciduousness: the proportion of decidu-

ous trees (those that shed all their leaves

simultaneously in winter or during the dry

season, that is, times of low growth rate)

to evergreens is highest in temperate zones,

while tropical trees are more likely to

retain their leaves since they grow more

continuously.

5 Lianas: certain angiosperms in tropical

forests grow as long, rope-like plants that

hang down from tall trees (see any Tarzan

ﬁ lm), but such plants are uncommon in

temperate forests.

6 Vessels in wood: in areas subject to freez-

ing or drying, the vascular canals possess

adaptations to prevent air ﬁ lling the canals

(a)

(b)

Figure 18.23 Fossil angiosperm remains from

North America. (a) Flower of an early box-like

plant, Spanomera, from the mid-Cretaceous of

Maryland (×10). (b) Leaf of the birch, Betula,

from the Eocene of British Columbia (×1).

(Courtesy of Peter Crane.)

Number of angiosperm families

Neocom

Cretaceous

SenonianTCeAlbianAptianB

Figure 18.24 Rapid radiation of the angiosperms

during the Cretaceous, shown by the rise in the

number of angiosperm families, from none at the

beginning of the Cretaceous to more than 35 by

the end of the period. Neocom, Neocomian;

B, Barremian; Ce, Cenomanian; T, Turonian.

(Based on information in various sources.)

506 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

when water is in short supply; the canals

are narrow and densely packed.

7 Growth rings: in areas subject to highly

seasonal climates, wood grows rapidly

during the warm or wet season, and slows

or stops growing when conditions are cold

and/or dry. The variation in growth ring

style indicates the degree of seasonality.

Abundant assemblages of leaves have been

recovered from several hundred Late Creta-

ceous localities in North America, and these

together show changes in leaf shapes of the

sort that reﬂ ect paleoclimates (Fig. 18.25a).

Measurements of the leaf-shape characters

noted above, based on ﬂ oras of numerous

species, can give a clear plot of paleotempera-

100 5060708090

30 + spp.

< 30 spp.

Cretaceous Tertiary

100

Leaf size

temperature

Mean annual

temperature (°C)( , )

Leaf size index (+)

Albian

Cenomanian

Turonian

Coniacian

Santonian

Campanian

Maastrichtian

Paleocene

Eocene

(b)

(a)

Aptian–Early Albian

Early Cenomanian

Middle–Late Albian

Figure 18.25 The evolution of angiosperm leaf shape and paleoclimate. (a) Samples of typical leaf

shapes from North American ﬂ oras spanning the mid-Cretaceous, showing variations in length, margins

and shapes. The average leaf size declines, suggesting an increase in temperature. (b) The leaf size index

(percentage of entire-margined species and average leaf size) for low-latitude North American ﬂ oras

through the Late Cretaceous shows ﬂ uctuations. These are interpreted as the result of changes in

temperature. (Based on information in Upchurch & Wolfe 1987.)

FOSSIL PLANTS 507

ture change in North America during the Late

Cretaceous (Fig. 18.25b). Temperatures

remained around 20–25˚C, with slight varia-

tions, until the last 5 myr of the Cretaceous,

when there was a dramatic rise in temperature

to 27˚C, then a drop, and a further rise in the

Early Tertiary.

Review questions

1 What is the current best evidence for the

greening of the land? Read around paleo-

botanical evidence for Precambrian, Cam-

brian and Ordovician plant fossils, and

molecular evidence for Neoproterozoic

dates for divergence of land plant groups.

Why do the dates seem to differ so

much?

2 Read about the detailed anatomy of Cook-

sonia, the ﬁ rst land plant to be known in

any real detail. Make a detailed recon-

struction, showing all the fossil evidence

for the different parts of the plant.

3 When did the ﬁ rst land plants achieve tree

size? Read about the 2007 discovery of

complete trees from the Gilboa locality in

New York State. How did this discovery

change our views about land plant

evolution?

4 What were the rain forests of the Carbon-

iferous like? Read DiMichele et al. (2007)

and related papers and web sites to ﬁ nd

out how new information about Carbon-

iferous ecosystems is being patched

together from new studies.

5 Why have angiosperms been so success-

ful? Trace the rise of the various angio-

sperm groups through the Cretaceous,

and list the supposed advantageous fea-

tures angiosperms have in comparison to

gymnosperms. Which of these adaptations

might have been most important in their

major diversiﬁ cation?