The Cretaceous World

The Cretaceous World
- 144 - 65 MY: a period of dramatic changes and
a transition towards the modern world -
Jarðsaga 1
- Saga Lífs og Lands –
Ólafur Ingólfsson

Late Jurassic-Early Cretaceous: Pangea is
ripping apart, creating new landscapes and
habitats and changing evolutionary conditions

Continental drift and Ocean spreading causes
transgressions in N America and Europe
Turonian Stage
(93.5-88.5 million
years ago)
Texas
Large scale transgression
from both
north and south
connects Arctic to
Gulf region,
dividing North
America into two
landmasses. Europe
undergoes a series
of transgressionregression
events

Climate and landscapes during the early Cretaceous
No major mountainbuilding
episode for
100 MY. Erosion
and deposition
prevailed.
Widespread plains
and lowlands,
deltas, swamps and
warm, shallow
seas.
There were no
glaciers anywhere
on Earth, and
global sea level
was 60m +

Early Cretaceous: A world steaming under
near-tropical conditions...
(cool temperate climates at very high latitudes, >70 o N and S)
... with incredible diversity of both fauna and flora, as well as optimal
conditions for evolution and occupation of new evolutionary niches...

Oceanic circulation

The fossil story reflecting warm conditions
Finds of Cretaceous fossil tree-trunks

The fossil story reflecting warm conditions

Cretaceous vs modern
temperatures
http://www.clas.ufl.edu/users/emartin/GLY3074S01/figures/cretgradient.htm

Laterite
Thick, red, greatly
weathered and
altered strata of
tropical ground.
Laterites are red
because silicates
have been leached
out, and iron and
aluminium salts now
predominate.
Horizons are unclear
and the nutrient
status of the soil is
low. Laterite is soft
but hardens rapidly
when to the air until
it has a brick-like
hardness.
Laterite and
Bauxite
Residual deposits formed
under tropical climate
conditions, where silicate-rich
rocks are
leched during a wet
season and subject to
strong evaporation during
dry season...
Bauxite
The chief ore of
aluminium,
consisting of
hydrous aluminium
oxides and
aluminous laterite.
It is a claylike
amorphous
material formed
by the weathering
of silicate rocks
under tropical
conditions. The
chief producers
are Australia,
Guinea, Jamaica,
Russia, Brazil, and
Surinam.

Crocodile-like animals
appeared in the Late Triassic,
and true croc´s in Jurassic
times. Some Cretaceous
crocodiles were awesome: the
giant Deionsuchus ('terrible
crocodile') was 12-14 m long
and had a skull 1.8 m long
Deltas and swamps...

Fossil remains of one of the
largest crocodilian species
ever to live have been
found in the Sahara by a
team led by Paul Sereno
(University of Chicago).
Sarcosuchus
The crocodile is believed to have
reached 14 m in length. The animal
lived about 110 million years ago in
what is now the windswept Ténéré
Desert in central Niger. The snout
and > 100 teeth were designed for
grabbing prey–fish, turtles and
dinosaurs that strayed too close.
This enormous reptile would have
made Africa’s ancient riverbanks a
dangerous place, even for a
dinosaur. The fossils belong to an
extinct creature named
Sarcosuchus imperator ("flesh
crocodile emperor")

Metriorhyncus probably moved
by sideways beatings of its tail
and it had evolved to be more
flexible and mobile than its landliving
relatives, making it faster
in water. Its skin was also less
scaly and more flexible than that
of the land-crocodiles, reducing
its resistance through the water.
Metriorhynchus –
purely aquatic crocodile
Metriorhynchus was ca. 3 m
long. It was a highly modified
aquatic predator which
had evolved from its cousins,
the land living crocodiles.
Apart from its long snout,it
bears little resemblance to
the conventional crocodile
shape. Metriorhynchus was
specially adapted to an
aquatic way of life with
flippers to replace the legs
and a vertical fin at the end
of its tail to help it swim.

The more
specialised
poisonous snakes
are not thought
to have evolved
until the middle
of the Tertiary
period, perhaps
30 MY ago.
Snakes and lizzards
Snakes are uncommon as fossils: They
have lightly constructed skeletons and
skulls comprised of separate moveable
sections and so are generally too
fragile to preserve well.
They were the last major group of
reptiles to appear in the fossil record.
One of the earliest known forms was
Dinilysia, meaning 'terrible destroyer',
which lived in the Early Cretaceous
period. It seems likely that snakes
evolved from aquatic lizards, although
most have now returned to life on land.

And then there were
the dinosaurs...
Cretaceous dinosaurs lived
on all Gondwana-Laurentia
continents, except
Antarctica

Development
towards heavier
herbivorae armour
and more vicious
predators

The break-up of
Pangea affected
dinosaur evolution
Dinosaurian paleobiogeography:
Temporally calibrated areagram
showing the breakup of Pangaea
into 10 major land areas by the
end of the Cretaceous. Checkered
bars indicate high-latitude connections
that may have persisted
into the Late Cretaceous. Five
paleogeographic reconstructions
divide continental areas into dry
land (black) and shallow (epieric)
seas (unshaded).

Different lines of evolution among the allosaurs
Dinosaurian paleobiogeography. Acrocanthosaurus, Giganotosaurus, and
Carcharodontosaurus, living on N America, S America, and Africa,
respectively, approximately 90-110 MY.

Dino´s walked across existing land bridges...
The geographic distribution of ceratops and some other groups during
Late Cretaceous can only be explained by dispersal across Beringia.

The Dino´s... The dinosaurs came in all varieties
including carnivores (meat-eaters),
herbivores (plant eaters) and
omnivores (all-eaters). Some were
small as a chicken and others as big
as a house, some of them flew like
birds. They occupied almost every
nisch...
Within the last decaded there has been a transformation in our understanding
of dinosaur paleobiology. They now are regarded as active,
agile, and adaptable, as opposed to huge, awkward, lumbering versions
of large reptiles.

HERBIVORES: Plant-eating dinosaurs were the most
common large animals in the Cretaceous ecosystems
A group of Omeisaurus, medium-sized
sauropods, are reconstructed browsing in a
conifer forest. Their physology is poorly
understood, and some aspects are widely
debated:
• Biomechanical problems. Some
paleobiologists argue that the mechanics
of muscle and tendon attachment would
not permit these animals to raise their
long necks that far above the horizontal.
• Blood pressure. It is difficult to imagine
how sufficient blood could have been
provided to the head at extreme elevation
to avoid unconsciousness when the head
was held up for any extended period.

The huge sauropods, so typical for Late
Jurassic dinosaurs, continued to live in
Gondwana, but died out in Laurassia
Titanosauria, Madagaskar
Paralititan stromeri, a
new, giant sauropod
dinosaur from Upper
Cretaceous mangrove
deposits in Egypt.

Laurassic herbivores relatively small
and heavily armed
Ankylosaurs: They were relatively
small, heavily armored Cretaceous
herbivores. Their ecology is poorly
understood, but their build suggests
that they fed primarily on vegetation
at ground level.
Hadrosaurs: A small group of
Telmatosaurus, hadrosaurs from the
Upper Cretaceous of central Europe.
Hadrosaurs were a very diverse group of
bipedal herbivores and were the most
important herbivore group during the
Cretaceous.

Ceratopsians
The most widely recognized ceratopsian dinosaur is
Triceratops, but this was a very diverse group of Cretaceous
herbivores and the only group that may have been
adaptively radiating near the end of the period.

No armour, quick and agile: an alternative
strategy...
Curiously, the most abundant and diverse of the Cretaceous
herbivores were the unarmoured ornithopod dinosaurs,
specifically the hypsilophodontids and iguanodontian lines,
all of which achieved cosmopolitan distribution.

Dinosaur Carnivores
Given the relatively large size of most dinosaur carnivores, they would
have required significant numbers of large prey animals to sustain
their populations. Carnivores would thus be much less numerous than
herbivores in any Mesozoic ecosystem.
An Ornithomimus, Cretaceous, USA.
These animals were probably very quick
and agile and may have preyed largely on
the eggs of other dinosaurs.

The Therapods
The theropod (meaning "beast-footed") dinosaurs are
a diverse group of bipedal saurischian dinosaurs. They
include the largest terrestrial carnivores ever. Birds
are the descendants of small nonflying theropods.
http://www.ucmp.berkeley.edu/diapsids/saurischia/theropoda.html

T-Rex and friends...
Tyrannosaurus rex was a huge (12 m long, about 6 m tall, 5-7 tons)
meat-eating dinosaur that lived during the late Cretaceous, 85-65 MY
ago. T. rex lived in a humid, semi-tropical environment, in open forests
with nearby rivers and in coastal forested swamps. Until recently,
Tyrannosaurus rex was the biggest known carnivorous dinosaur; Giganotosaurus
and Carcharodontosaurus were slightly bigger.

How fast did the dinosaurs move:
There is a general relationship between speed and stride
length in living animals. This can be used to estimate how
fast the dinosaurs were:
• Sauropods and ankylosaurs were slowest, ~ 3-5
km/hr
• Most ornithopods were faster, ~ 5-7 km/hr
• Theropod predators were fastest, ~ 10 km/hr,
bursts up to 40-50 km/hr

Velociraptor ("Speedy Thief“)
Velociraptor was a fastrunning,
two-legged dinosaur.
This meat-eater had about 80
very sharp, curved teeth in a
long, flat snout; some of the
teeth were over 2.5 cm long.
This predator had an s-shaped
neck, arms with three-fingered
clawed hands, long thin legs,
and four-toed clawed feet.
Velociraptor's head was about
18 cm long. Velociraptor may
have been able to run up to
roughly 40 km/hr for short
bursts.

Velociraptor’s murder weapon
A 9 cm long, sickle-like,
retractible claw was on
the middle toe of each
foot. This claw was its
main weapon, and could
probably kill most of its
prey (plant-eaters like
hadrosaurs) easily.

A small but smart killer
Velociraptor was 1.5-2 m long, and 1 m tall. It may have
weighed about 7-15 kg. It had a stiff tail that worked as
a counterbalance and let it make very quick turns.
Velociraptor's brain was relatively large in comparison to
its body size (this is true for all the Dromaeosaurid
dinosaurs, who were the most intelligent dinosaurs).

How brainy were the dinosaurs?
• Big Sauropods and Stegosaurs:
EQ of ~0.1-0.6
• Ceratopsians and Ornithopods:
EQ of 0.5-1.5
• Big Theropods: 0.9-1.9
• Some smaller Theropods, like
velociraptor: EQ 5-5.8
EQ is the ratio of the brain weight of the animal to the brain weight
of a "typical" animal of the same body weight. We are comparing
dinosaurs to reptiles, but even the “dumbest” mammal has twice the
brain size of a similar sized reptile

Are the dinosaurs
still around (as
birds)?
During Late Cretaceous,
there was an
extraordinary range of
birds and dinosaur-like
protobirds. It is impossible
to tell where
dinosaurs ended and
birds began...
There are numerous striking
similarities between
carnivorous dinosaurs and
birds.

Oviraptor
Oviraptor (“Egg thief”), Upper Cretaceous (85-75 MY);
Length (up to) 1.8 m; omnivorous; Found in Mongolia

Ornithomimidae ("Bird Mimics")
Ornithomimids were a distinctive group of theropod
dinosaurs, who are a good example of convergent evolution
with the birds such as ostriches. Ornithomimids were
generally slender, lightly-framed, and reached huge sizes
(some attaining lengths of 7 m).

Feathered dinosaurs
A new range of fossil finds, mostly from China, are revealing that a
large number of small dinosaurs were covered by feathers
Sinornithosaurus was a small dinosaur that probably fed on animals
such as reptiles and mammals. Like larger raptors the animal may have
attacked with a jumping stance, as shown here. Although quite birdlike,
this dinosaur could not glide or fly, which raises the issue as to
why it evolved feathers.

Why Feathers?
• Sexual Display. One possibility is
that feathers may have served to
enhance sexual display as part of
mating behaviour.
• Insulation. One important role for
feathers may well have been
insulation. If some dinosaurs were
warm blooded, small individuals
would face a problem of significant
heat loss due to an unfavorable
(high) surface to volume ratio.
• Large vs. Small Bodies. The
hatchling has a covering of
feathers to assist in retaining body
heat, but the feathers are lost as
the animal grows to adult size.

Caudipteryx
Yet another feathered dinosaur/bird
from China...

Uenlagia (“half-bird”)
Several features of Unenlagia
(originally described from
Upper Cretaceous of
Argentina) are more birdlike
than in any other non-avian
theropod so far discovered.
The evidence suggests that it
could flap its arm, although
Unenlagia was much too heavy
to fly with such a short wing.

The development of birds...
The Jurassic Archaeopteryx was one transitional
form between birds and reptiles.
Unlike all living birds, Archaeopteryx had
a full set of teeth, a flat breastbone, a
long, bony tail, and three claws on the wing
which could have still been used to grasp
prey (or maybe trees). However, its
feathers, wings, wishbone and reduced
fingers are all characteristics of birds.
Ichthyornis: This ‘fish bird’ was an 30
cm long bird of the Cretaceous period
that dived to catch fish. Ichthyornis
could probably fly and had long wings.
It had teeth in its jaws, unlike modern
birds. Its remains were found in
Kansas, USA.

Ichthyornis
Ichthyornis was
first described in
1872, from sediments
in Kansas, and
originally thought to
be a marine reptile.

Birds of the Cretaceous
The evolution of birds is not well known, since they
preserve badly as fossils
Hesperornis or ‘western
bird’ was a >1 m long
flightless bird of the
Late Cretaceous period.
Fossil skeletons have
been found in Kansas and
Alberta, Canada. This
fish-eating bird had
large, possibly webbed
feet and may have been
a good swimmer and
diver.

Enantiornithes
http://www.sino-collector.com/eng/_private/cjyd/zjlt/hjs-hs/hjs02-3.htm

Action in the skies
A flock of Criorhynchu soars above a longnecked
Elasmosaurus, while the ternlike
Ichthyorni skims the waves at lower left.

...action in the skies...
The Pterosaur
Quetzalcoatlus
northropi had a
wingspan of 12-
13 m, making it
the largest
known flyer of
all time...
The giant Quetzalcoatlus has been compared with large modern birds
such as condors and eagles and it has been concluded that, like them, it
ate carrion. But the anatomical evidence does not support this.
Quetzalcoatlus had a long inflexible neck that would not have been
desirable for vulture-like feeding. Its long, tweezer-pointed, and
toothless jaws were not suited for tearing apart dinosaur cadavers, and
are more suggestive of a diet of fish or molluscs and arthropods in
shallow flood basins.

The diatoms (kísilþörungar) appear
They are among the most important aquatic micro-organisms today:
they are extremely abundant both in the plankton and in sediments in
marine and freshwater ecosystems, and because they are photosynthetic
they are an important food source for marine organisms. Some
Cretaceous rocks are formed almost entirely of fossil diatoms, and are
known as diatomite or diatomaceous earth. These deposits are mined
commercially as abrasives and filtering aids. Analysis of fossil diatom
assemblages may also provide important information on past
environmental conditions.

Enormous Cretaceous chalk deposisits
The massive chalk deposits (>200 m) of NW-Europe
(Denmark, England, N France) are composed of the armour
plates of calacareous nannoplankton (kalkþörungar)

Life on the sea floor
Life on the sea-floor began to
take on a modern appearance
during the Cretaceous Period.
Cretaceous Oysters – some grew
to very large sizes

Rudists build reefs
Rudists were the dominating Cretaceous reef-builders, at the
expense of the corals
Rudist: An extinct bivalve mollusk from the Jurassic and Cretaceous that
had two different sized and shaped shells; they usually were attached to
the substrate and were either solitary or in reeflike masses.

Reef builders
since the
Permian

The shallow seas
Helioceras was a
loosely-coiled
cephalopod that
lived in the
shallow seas that
bisected North
America in the
Cretaceous.
A gigantic (0.3 m)
ammonite shell of
Placenticeras

A very large
Cretaceous
marine turtle
(Archelon)
The shallow seas...
Mosasaurs were large marine lizards up to 9
m in length. They preyed largely on fish
Plesiosaurs were marine
reptiles with a stocky body,
four large flippers, and a
long tail.

The mosasaurs
are distinct
relatives of
modern snakes
and perhaps
the Komodo
Dragon of
Indonesia
A mosasaur in action
http://www.oceansofkansas.com/mosasaur.html

http://www.oceansofkansas.com/Greatrep.html

Reconstruction of marine life in upper
Cretaceous of USA

The Teleost fishes (beinfiskar)
develop
Teleosts are characterized by symmetrical tails, round
scales, specialized fins and short jaws
Diplomystus brevissimus
By Late Cretaceous time,
a wide variety of teleosts
existed, including
close relatives of the
modern sunfish (“tunglfiskur”),
carp (“vatnakarpi”),
swordfish
(“sverðfiskur”), eel (“áll”)
and salmon (“lax”).

Fish-in-a-fish
Xiphactinus audax, (Bulldog Fish), was a species of very
large (5 m) predatory fish that lived in the ocean during
the Late Cretaceous.

Enter the mammals...
The three modern mammal groups:
monotremes (nefdýr), marsupials
(pungdýr), and placentals (legkökudýr)
originate during the Cretaceous.
Echydna and Platyphus
Bandycoot, a small
marsupial
Koala
The earliest mammals,
such as Morganucodon
started to develop during
latest Triassic and early
Jurassic. Most Mesozoic
animals were small and
would remain so until the
extintion of the dinosaurs
opened niches that
permitted the adaptive
radiation of mammals in
the early Cenozoic.

Geological ranges
for mammals

Insects develop before the appearance of
flowering plants
Insects make up over threefourths
of all known animal species
on the planet...
A 95 million year old fossil insect
(a wasp) in amber from the
Raritan formation of New Jersey
The oldest true flies are Triassic in
age; butterflies appear in the
Jurassic; and by the end of the
Cretaceous, almost all the familiar
true flies groups had appeared.
Insects and flies, as far as we can
tell, were completely unaffected by
the extinction event at the end of
the Cretaceous...

Ants, termites, wasps, bees...
They all originated during the Cretaceous

The sudden emergence of flowering plants
More than one-hundred years
ago, Darwin called the origin of
angiosperms an "abominable
mystery".
One of the biggest questions
about early angiosperms,
besides their origin, is the
nature of their growth habit.
Were the first angiosperms
woody trees and shrubs, or were
they small herbs?
First appearing in the tropics during the Lower Cretaceous, around
125 MY ago, the flowering plants first radiated in the middle Cretaceous,
about 100 million years ago. By the end of the Cretaceous, a
number of forms had evolved that any modern botanist would
recognize. No fossils showing a transition from gymnosperm to
angiosperm have been discovered.

The flowering plants little secrets of
success...
1. Double fertilization. First fertilization produces egg
within the ovary (eggleg); second fertilization produces a
storey of food for the seed.
A photomicrograph of lily (lilja) double
fertilization.
The rapid manufacturing of
this food supply allows for
the quick release of a well
fortified seed.
Most gymnosperms have
reproductive cycles of 18-
24 months; angiosperms
have reproductive cycles
of few weeks!

Pollinating by insects...
2. Symbiotic relationships between flowering plants and
insects.
Isects benefit from the nutritious
nectar that the flowers provide;
The flowers benefit because the
insects (unknowingly) carry pollen
from one flower to another,
fertilizing the plants on which they
feed

-Gymnosperms dominated the Mesozoic landscape,
but are today mostly confined to cooler temperate
climates
- Angiosperms dominate since the Late Mesozoic

Oldest flowering plant in the world
Chinese and U.S. scientists
have identified what is
believed to be the world's
oldest flowering plant. The
140-million-year-old fossil was
found in northeastern China.
Sun Ge, a researcher with the
Academia Sinica in Nanjing,
China, and David Dilcher with
the University of Florida,
worked together earlier this
year to identify the specimen,
which predates the previous
oldest-known flower by 25
million years.

Did dinosaur grazing
boost flowering
plants?

Angiosperms and the modern world...
• Nearly all of our food comes from flowering plants:
grains, beans, nuts, fruits, vegetables, herbs and spices;
as do tea, coffee, chocolate, wine, beer, tequila...
• Angiosperms are the staple for herbivores that we in
turn eat: sheep, cattle, goats, pigs... you name it...
• Much of our clothing comes from them as well: cotton
and linen are made from "fibers" of flowering plants, as
are rope and many commercial dyes are extracted from
other flowering plants.
• We also owe them credit for a large number of our
drugs, including aspirin, numerous prescribed drugs and
controlled drugs such as opium, cocaine, marijuana, and
tobacco.

Late Cretaceous: Active plate boundaries and
mountain building start changing the scene...

The Cordilleran
orogeny
The Rockies were formed
in the Mesozoic and Early
Cenozoic eras during the
Cordilleran orogeny. They
are geologically complex,
with remnants of an
ancestral Rocky Mt.
system and evidence that
uplift, which involved
almost all mountainbuilding
processes,
occurred as a series of
pulses over millions of
years. The mountains have
since been eroded to
expose ancient crystalline
cores flanked by thick
upturned layers of
sedimentary rocks.

• Cordilleran orogeny: A protracted episode of
deformation affecting the western margin of North
America from Jurassic to Early Cenozoic time; typically
divided into three separate phases called the Nevadan,
Sevier, and Laramide orogenies.
•CretaceousInteriorSeaway:An interior seaway that
existed during the Late Cretaceous; formed when
northward-transgressing waters from the Gulf of
Mexico joined with southward-transgressing water from
the Arctic; effectively divided North America into two
large landmasses.
• Laramide orogeny: The Late Cretaceous to Early
Cenozoic phase of the Cordilleran orogeny; responsible
for many of the structural features of the present-day
Rocky Mountains.

The Laramide orogeny
A series of mountain-building events that affected much
of western North America in Late Cretaceous and Early
Tertiary time. Evidence of the Laramide orogeny is
present from Mexico to Alaska.

Laramide thrusts
The Keystone thrust. This fault shows the Cambrian
Bonanza King formation (gray) over folded Jurassic
Nugget sandstone (red).

Rocky Mts landscapes

Summing up the Cretaceous
• Latitudional temperature gradients were gentle –
warm even at high latitudes and no glaciers
• The Cretaceous was an extreme greenhouse situation
• Gondwana broke apart during the Cretaceous Period,
forming the South Atlantic. The Tethys seaway
existed, that carried warm waters through the
Mediterranean region
• On land, flowering plants diversified and evolved,
together with the insects
• The mammals evolve and diversify
• In the sea, the phytoplankton assumes a modern
character, and crabs and teleost fishes evolve and
diversify significantly

K/T Boundary
The Cretaceous-Tertiary boundary is marked by a mass
extinction: 50-60% of all living species of animals and
plants became extinct. Caused by a large meteorite
impact?

Causes-effects of the 65 MY K/T extinction
During the K-T extinction (65
MY ago) 85% of all species
disappeared. The dinosaurs
perished in the K-T extinction,
and several other terrestrial
and marine groups were also
severely affected or eliminated.
Among those that perished
were the pterosaurs, belemnids,
many species of plants, ammonides
and marine reptiles. Groups
which were severly affected
included planktonic foraminifera,
diatoms, molluscs and fish.
Remarkably, most mammals,
birds, turtles, crocodiles,
lizards, snakes, and amphibians
were primarily unaffected by
the K/T extinction...
Evidence for catastrophism
at the K/T boundary is found
in a layer containing unusually
high concentrations of
Iridium, originating either
from the earth's mantle or
from extra-terrestrial
meteors. This layer has been
found found in both marine
and terrestrial sediments, at
many sites around the world.

Cretaceous
extinctions
90 million years ago 80 70 65
?
60
Figure 15.5

Meteorite Impact or Volcanic Eruptions?
• The widespread distribution of the Iridium layer may have been
caused by a meteorite impact. Recent research suggests that the
impact site may have been in the Yucatan Peninsula of Mexico.
• The high concentrations of Iridium in the boundary layer could be
result of massive volcanic eruptions at the K/T boundary: either in the
Deccan Traps (India and Pakistan) or at the Iceland hot spot. These
eruptions produced thousands of km 3 of lava and enormous amounts of
ash. They could have affected global climate and ocean chemistry.
• Both volcanic and meteorite impact hypotheses are viable mechanisms
for causing the K/T mass extinction, although the latter is more
popular...

Major events of the Cretaceous Period

References, web resources
• Stanley, Earth System History, chapter 17.
• http://www.ucmp.berkeley.edu/mesozoic/cretaceous/cretaceous.html
• http://www.bbc.co.uk/dinosaurs/fact_files/
• http://www.ucmp.berkeley.edu/diapsids/saurischia/theropoda.html
• http://www.sino-collector.com/eng/_private/cjyd/zjlt/hjs-hs/hjs02-3.htm
• http://www.palaeos.com/Mesozoic/Cretaceous/Cretaceous.htm
• http://www.oceansofkansas.com/
• http://www.scotese.com/
• http://jan.ucc.nau.edu/~rcb7/globaltext2.html
• http://www.nytimes.com/library/national/science/122199sci-archaeoflowers.html
• http://www.napa.ufl.edu/98news/flowerph.htm
• http://www.colby.edu/~ragastal/Paleobotany/angiorigins.htm
• http://www.pbs.org/wgbh/evolution/library/03/4/l_034_01.html