Phylum Chordata
4. Notochord. A stiff cartilaginous rod which
supports the nerve cord.
5. Post-anal tail. This is an extension of the
body past the anal opening.
6. Blood that circulates forward in a main
ventral vessel and backward in a dorsal
vessel.
Phylum Chordata
Subphylum Urochordata
• Primitive chordates. Sea squirts,
ascidians, or tunicates. Larval forms have
notochord in tail region.
• Chief characteristics: Adults have sac-like
bodies, ranging in size from less than 1
mm to a few cm. Larval form resembles a
tadpole and has a notochord, dorsal
tubular nerve cord, gill slits, and post-anal
tail.
Phylum Chordata
Subphylum Urochordata
• Geologic range: not known
• Mode of life:
– Inhabit overhangs or shaded areas in the low
intertidal and subtidal zone.
– Most live attached as adults.
– Filter feeders.
– Behavior resembles that of a sponge.
– Body contracts abruptly expelling water,
giving them the name "sea squirts".
Phylum Chordata
Subphylum Cephalochordata
• Primitive chordates. Lancelets, Amphioxus,
Branchiostoma. Small marine animals with fishlike bodies and notochord.
• Geologic range: Cambrian to Recent.
• Mode of life: Bottom dwellers. Lancelets spend
much of their time burrowing in the sand in warm,
coastal, marine environments. Filter feeders.
Relatively sessile but capable of swimming.
• Significance: An ancestor to the vertebrates
resembled a lancelet-like creature (Pikaia).
Chief characteristics:
–
–
–
–
Lancelets resemble a small, colorless anchovy fillet.
No obvious eyes or lateral fins.
Worm-like.
Has segmented axial muscles, gill slits, a dorsal hollow
nerve cord, a notochord, and a post-anal tail.
– No solid skeleton. Nothing resembling a vertebral
column.
What ARE conodonts?
• The conodonts were previously placed in a
separate phylum (Phylum Conodonta),
because their affinities were unknown.
• The current interpretation places the
conodont-bearing animal with the
Chordates in Phylum Chordata.
• The organism from which they came is not
known with certainty.
Examples of various shapes of conodont elements.
Images courtesy of Anita Harris, U. S. Geological Survey.
Conodonts
• Chief characteristics:
– Microscopic in size
– Composed of calcium fluorapatite.
– Shape - cone-shaped teeth, or bars with rows
of tooth-like denticles, or irregular knobby
plates called platforms.
– Each conodont element is part of a larger
organism. Most fossil occurrences are of
disassociated elements, but occasionally they
are found arranged in specific assemblages
or “apparatuses”.
Conodonts
• Name: Conodont means "cone" + "teeth"
(dont)
• Geologic range: Neoproterozoic to Late
Triassic.
• Mode of life: Marine, free-swimming.
Conodonts
• Significance:
– Useful in biostratigraphy
– Useful in marine paleoenvironmental
interpretation
– Their color is a good indicator of the
temperature to which the rock has been
subjected. (This is important in determining
whether oil or gas may be present in the
rock).
Conodonts
The color indicates thermal history and burial
temperatures. Darker color indicates higher
temperature. Temperatures are important to
determine whether petroleum may have been
generated in the rock, or whether temperatures
were too high for petroleum to be preserved.
What WAS the conodont animal?
• Several fossils of conodont animals have
been reported, but most were discredited
and reinterpreted as an organism which
had actually eaten the conodont animal,
because the conodont elements were only
in the stomach or digestive tract.
What WAS the conodont animal?
• Sketch of a conodont animal published in
1993 from the Lower Carboniferous of
Scotland.
• The conodont animal is found as softbodied impressions. The animals lack
skeletal parts except for the conodonts,
which occur in the mouth region.
What WAS the conodont animal?
• A fossil discovered in 1995 in the Ordovician
Soom Shale of South Africa contains soft bodied
remains of an animal with an elongated eel-like
body.
• The animal had an eye, and had V-shaped
musculature along the sides of the body, as in
the amphioxus or lancelet.
• The organism has a longitudinal band which
may mark the position of the notochord.
What were the conodont elements
used for in the conodont animal?
• Internal laminated structures within conodont
elements indicate that new lamellae were added
on the outer surface of many elements,
suggesting that they were an internal skeletal
appatatus, covered with tissue, rather than being
used as teeth.
• They may have been supports for a foodgathering apparatus.
• Some conodonts show evidence of having been
broken and subsequently repaired.
• The function of the conodont apparatus is not
known.
Phylum Chordata
Subphylum Vertebrata
The vertebrates are animals with:
• Segmented backbone consisting of vertebrae
• Definite head with a skull that encloses a brain
• Ventrally-located heart
• Well-developed sense organs
• Notochord is supplemented or replaced by
cartilaginous or bony vertebrae.
• Arches of the vertebrae encircle and protect a
hollow spinal cord.
Phylum Chordata
Subphylum Vertebrata
• Mode of Life:
– Includes both water-dwelling and landdwelling tetrapods (from the Latin, meaning
four feet).
– Some walk on four legs and some walk only
on the hind legs (bipedal).
– In some, forelimbs are modified into wings.
– In some, the limbs have been modified into
flippers.
• Geologic range: Cambrian to Recent.
Phylum Chordata
Subphylum Vertebrata
Two major groups of vertebrates:
• Non-amniotic vertebrates - Egg lacks a covering
and must be fertilized externally. Must be wet or
in water to reproduce.
– Fish
– Amphibians
• Amniotic vertebrates - Amniotes. Internal
fertilization and an amniotic egg (enclosed egg).
Water is not required for reproduction.
– Reptiles
– Birds
– Mammals
Amniotic Egg
Amnion (or amniotic membrane)
encloses the embryo in water
(amniotic fluid).
Allantois is a reservoir for waste
and provides for gas diffusion. It
becomes the urinary bladder in
the adult.
Chorion provides a protective
membrane around the egg.
Yolk is a storage area for fats,
proteins, and other nutrients food for the embryo.
Significance of the Amniotic Egg
• Provided freedom from dependency on
water bodies.
• Helped the vertebrates live in diverse
types of terrestrial environments.
• An important milestone in the evolution of
vertebrates.
The Fishes
There are five classes of fishes.
1. Agnathids or jawless fish
2. Acanthodians or spiny fish with jaws. Extinct.
3. Placoderms or plate skinned fish with jaws.
Extinct.
4. Chondrichthyes or fish with cartilaginous
skeletons, including sharks, rays, and skates.
5. Osteichthyes or bony fishes. Most modern fish.
Led to evolution of tetrapods.
Geologic ranges
of the five
classes of fishes
The Oldest Fish
• The oldest known fish is from the
Cambrian of China (about 535 m.y. old),
found in the Chengjiang fossil site in
Yunnan Province,
Class Agnatha
• Jawless fishes, including the living
lampreys and hagfishes as well as extinct
ostracoderms
• Name: "A-" means "without", and "gnatha"
means "jaws".
• Chief characteristics: Fish without jaws.
• Mode of life: Swimmers.
Class Agnatha
• Geologic range: Cambrian to Recent.
Ostracoderms were Ordovician to Devonian.
• Jawless fishes are present in the Harding
Sandstone (Lower Ordovician) of Colorado.
Also found in Lower Ordovician rocks in
Australia and Bolivia. Includes Astraspis.
Astraspis, an Ordovician
jawless fish
Ostracoderms
• A group of armored jawless fishes called
the ostracoderms (name means "shell
skin") lived in the Early Paleozoic.
• Ostracoderms were mainly small, sluggish
fish that were filter feeders or "mud
strainers".
Ostracoderms
• The armor was made of
bony material, and served
as protection from predators
or for storing seasonally
available phosphorous.
• Bone is made of apatite,
which contains
phosphorous.
Evolution of Jaws
• The first fish with jaws appeared in
nonmarine rocks in the Late Silurian.
• The evolution of the jaw expanded the
adaptive range of vertebrates.
• Used for biting and grasping.
• Led to more varied and active ways of life,
and to new sources of food.
Evolution of Jaws
• Origin of jaws - two hypotheses:
– Modification of a front pair of bone or cartilage
gill supports.
– More recent hypothesis: Modification of the
velum, a structure used in respiration and
feeding in lamprey larvae.
• Both hypotheses are based on anatomy
and embryology of living fishes.
Class Acanthodii
•
•
•
•
Acanthodians or spiny fishes.
The first fishes to have jaws.
Name: "Acanthos" means "spiny".
Chief characteristics: Primitive spiny fishes
with jaws.
• Geologic range: Late Silurian to Permian. Most
numerous during the Devonian. Extinct.
• Mode of life: Swimmers. Nonmarine.
Class Placodermi
Dunkleosteus
• Placoderms or "plate-skinned"
fishes.
• Name: "Placo-" means plate and
"derm" means "skin".
• Chief characteristics: Fish with
jaws and armor plating.
• Geologic range: Late Silurian to
Late Devonian. Extinct.
• Mode of life: Swimmers. Some
were large carnivorous predators,
such as Dunkleosteus, which grew
to about 9 m long
Class Chondrichthyes - Sharks
• Sharks, rays, and skates
• Name: From "chondros", meaning "cartilage",
and "icthyes" meaning "fish".
• Chief characteristics: Cartilaginous fishes.
Skeleton made of cartilage not bone. Rarely
preserved.
• Geologic range: Middle Paleozoic (Late Silurian
or Devonian) to Recent.
• Mode of life: Swimmers. Marine, except one
Late Carboniferous freshwater genus.
• The genus Cladoselache, is found in Devonian
shales on the southern shore of Lake Erie.
Class Osteichthyes - Bony Fishes
• Bony fishes
• Name: "Osteo" means "bone"
and "ichthyes" means "fish".
• Chief characteristics: Skeleton of bone, not
cartilage. Modern bony fishes are of this type.
• Geologic range: Devonian to Recent.
• Mode of life: Swimmers. Marine and freshwater.
The earliest lived in freshwater.
• The most numerous, varied, and successful of
all aquatic vertebrates.
Class Osteichthyes - Bony Fishes
• Bony fishes played a key role in the
evolution of tetrapods (four-legged
animals).
• Two types of bony fish are significant:
– Subclass Actinopterygii - the ray-finned fish.
– Subclass Sarcopterygii - the lobe-finned fish
or lungfish.
Subclass Actinopterygii
•
•
•
•
Ray-finned fish
Dominant fishes in the world today.
No muscular base to the paired fins.
Fins are thin structures supported by
radiating rods or rays.
• First appeared in Devonian freshwater
lakes and streams, and then expanded
their geographic range to the sea.
Subclass Sarcopterygii
- Lobe-finned fish or Lungfish
Chief Characteristics:
• Leg-like fins:
Muscular fins used to "walk" on pond or stream
bottoms.
• Lungs:
A pair of openings in the roof of the mouth led to
nostrils.
Able to rise to the surface and breathe air with
lungs when the water became foul or stagnant.
Some had both lungs and gills.
Subclass Sarcopterygii –
Lobe-finned fish or Lungfish
• Geologic range: Late Devonian to Recent
• Significance: This group gave rise to the
amphibians and other tetrapods (fourlegged animals).
• Types of sarcopterygians:
– Order Dipnoi or dipnoans
– Order Crossopterygii or crossopterygians –
the ancestor of the amphibians
Order Dipnoi - dipnoans
• Chief characteristics: They can breathe with
lungs during the dry season, and can burrow
into the mud during droughts.
• Name: Dipnoi means "double breather"
• Significance: This group did not lead to
tetrapods, but includes interesting freshwater
lungfish living today in Australia, Africa and
South America.
Devonian lungfish, Dipterus
Order Crossopterygii crossopterygians
• Chief characteristics:
– Short, muscular, paired fins.
– Had a single limb bone called the humerus,
followed by the radius and ulna in front fins,
and the tibia and fibula in hind fins.
• The adaptation assisted movement in shallow
water, and allowed the fish to move from a
stagnant or drying body of water, to another
body of water.
Order Crossopterygii crossopterygians
• Significance: Considered to be ancestral to the
amphibians because of the arrangement of
bones in their fins, the pattern of bones of the
skull, and the structure of their teeth.
Late Devonian crossopterygian lungfish, Eusthenopteron.
Types of crossopterygian fish
1. Rhipidistians - This group led to the amphibians
2. Coelacanths - Lobe-finned crossopterygian fish
invaded the sea and gave rise to coelacanths.
Coelacanths were long-believed to be extinct
and are considered to be living fossils. One
was caught in 1938 near Madagascar. More
have been caught since.
Latimeria, a modern coelacanth. Tail
is similar to that of Eusthenopteron,
but very different from that of rayfinned fish.
Similarities between Crossopterygian
Fish and Amphibians
1. The same limb bones are present.
Early amphibian (left). Crossopterygian fish (right).
The major limb bones are coded r, u and h.
r = radius
u = ulna
h = humurus
Similarities between Crossopterygian
Fish and Amphibians
2. The same skull bones are present.
Crossopterygian fish (left) and the Devonian amphibian,
Ichthyostega (right).
The Advent of Tetrapods
• Tens of millions of generations passed
before crossopterygian fish evolved into
animals that could live entirely on land.
The early tetrapods (four-legged animals)
continued to return to water to lay their
fish-like, naked eggs. Fish-like tadpoles
hatched from these eggs, which used gills
for respiration.
Anatomical changes associated
with the shift from water to land:
1. Three-chambered heart developed and
functioned to pump blood more efficiently to
the lungs
2. Limb and girdle bones altered to support the
body above the ground
3. Spinal column changed to become sturdy but
flexible
4. Fish spiracle (vestigial gill slit) became
amphibian eustachian tube and middle ear
Anatomical changes associated
with the shift from water to land:
5. Bones of the ear changed to function
better in air than in water (modification of
hyomandibular bone that propped fish
braincase and upper jaw together, into
an ear ossicle called the stapes)
6. Eardrum (tympanic membrane) formed
across a notch in the skull
Amphibians are interpreted to be descended
from crossopterygian fishes because of:
1. Arrangement of bones in amphibian limbs
compared with the fins of crossopterygian fish
2. Pattern of bones of the skull
3. Structure of the teeth - highly infolded like a
maze (or labyrinth), and called labyrinthodont
teeth.
4. Bones of the spinal column in early forms.
Class Amphibia –
The Amphibians
• Name: "Amphi" means "both" or "double",
and "bios" means "life". "Amphibios"
means living a double life, referring to
living in water and on the land.
• Chief characteristics and mode of life:
Amphibians can live on the land as adults,
but they lay their eggs in water. Young
amphibians live in the water and are fishlike (tadpoles).
The Amphibians
• Geologic range: Late Devonian to Recent.
• For 50 million years, from the Late
Devonian to the Middle Carboniferous,
amphibians were the only vertebrates to
the inhabit the land. Some adult
amphibians reverted to an aquatic mode of
life, while others retained a terrestrial
lifestyle.
Ichthyostega – The First
Amphibian
• The first terrestrial vertebrate, Ichthyostega,
appeared in the Late Devonian, about 375 m.y. ago
• Found in freshwater deposits.
• "Ichthyo" means "fish" and "stega" means "roof" or
"cover" (probably referring to the bones in the roof
of the skull).
Ichthyostega – The First
Amphibian
• Ichthyostega retained many features of its fish
ancestors, such as:
– Scales
– Similar skull structure, including arrangement
of nostrils
– Loosely connected fish-like spinal column
• It also had a number of unique traits such as:
– Five-toed limbs
– Pelvic and pectoral girdles, allowing it to walk
on land
• Amphibians inhabited the Carboniferous
coal swamps, and were abundant and
varied.
• They had several different modes of life,
including some with an aquatic lifestyle (as
suggested by features such as a flattened
body and skull, reduced limbs, and a
slender snake-like body), and some that
were clearly land dwellers (with stout
limbs, short body and tail).
Skull of Neopteroplax, 290 m.y. ago, aquatic
amphibian from the Late Carboniferous of Ohio.
Features suggesting an aquatic lifestyle include
a flattened body and skull, reduced limbs, and a
slender snake-like body.
• Some Carboniferous amphibians were quite large,
ranging up to 20 feet (about 6-7 m) long. In
contrast, most living amphibians are small.
• Eryops, large amphibian (about 5 ft or nearly 2 m
long) from the Permian.
• Eryops had short, powerful limbs, which suggest
that it was primarily a land dweller.
• Some Permian amphibians, such as Seymouria,
exhibit a combination of amphibian and reptilian
features.
• Seymouria, a land-dwelling amphibian from the
Lower Permian of Texas, 260 m.y. ago, was less
than 3 ft long.
• Note stout limbs, short body and tail.
• A primitive amphibian similar to Seymouria was
probably ancestral to the reptiles.
Two major groups of vertebrates:
• Non-amniotic vertebrates - Egg lacks a covering
and must be fertilized externally. Must be wet or
in water to reproduce.
– Fish
– Amphibians
• Amniotic vertebrates - Amniotes. Internal
fertilization and an amniotic egg (enclosed egg).
Water is not required for reproduction.
– Reptiles
– Birds
– Mammals
Characteristics of the
Amniotic Egg
• Durable outer shell protects embryo from drying
• Egg can be laid on land
• Yolky part of egg provides nutrition; sac contains
embryo and another sac collects waste
products.
• Eliminated need to lay eggs in water, allowing
vertebrates to live and reproduce on dry land for
the first time.
• Amniotic egg probably evolved in Carboniferous.
• First fossil eggs are Early Permian
Amniotic Egg
Amnion (or amniotic membrane)
encloses the embryo in water
(amniotic fluid).
Allantois is a reservoir for waste
and provides for gas diffusion. It
becomes the urinary bladder in
the adult.
Chorion provides a protective
membrane around the egg.
Yolk is a storage area for fats,
proteins, and other nutrients food for the embryo.
Significance of the Amniotic Egg
• Provided freedom from dependency on
water bodies.
• Helped the vertebrates live in diverse
types of terrestrial environments.
• An important milestone in the evolution of
vertebrates.
Class Reptilia - The Reptiles
• Name: From "reptilis" meaning "creeping".
• Chief characteristics: Skull characteristics
that distinguish reptiles from amphibians:
– Reptile skull is high and narrow, compared
with the low, broad amphibian skull.
– In reptiles, the roof of the mouth is arched,
with small openings. In amphibians, it is flat
with large openings.
Class Reptilia - The Reptiles
• Mode of life: Complete colonization of land was
achieved by the reptiles, which can lay their
eggs on dry land.
• Geologic range: Pennsylvanian to Recent.
• The oldest reptile fossils, genus Hylonomus,
(300 m.y. old) are found in Nova Scotia inside
fossilized hollow trees filled with sediment.
These reptiles were about 24 cm (1 ft) long.
They resemble modern insect-eating lizards.
Vertebrate Skulls
Vertebrates can be distinguished on the position
and number of skull openings behind the eye.
– Anapsida (no holes) - amphibians, the
earliest known reptile (Hylonomus), and
turtles
– Diapsida (two holes) - dinosaurs, flying
reptiles, birds, and living reptiles except
turtles
– Euryapsida (upper hole only) - extinct
marine reptiles
– Synapsida (lower hole only) pelycosaurs, therapsids, and mammals
Diagram
showing the
evolution of
reptiles and
synapsids.
Class Synapsida The Synapsids
• The synapsids had diverged from the
reptiles by the Late Carboniferous.
• The synapsids were long considered to be
a subclass of reptile, but more recent
cladistic analysis shows that they diverged
from ancestors completely different than
Hylonomus and other true reptiles.
The Synapsids
• The synapsids were the dominant
terrestrial vertebrate in the Permian.
• This group was formerly called the
"mammal-like reptiles", however the name
has been abandoned because they are
not really reptiles.
• Synapsids include the pelycosaurs and the
therapsids.
Pelycosaurs
• Several species of pelycosaurs had fins or "sails"
on their backs, supported by rod-like extensions
of their vertebrae. These sails may have been
used as temperature regulating mechanisms.
• Pelycosaurs lived in the Carboniferous and
Permian. Sail-backed forms are Permian.
The Permian pelycosaur,
Edaphosaurus.
Pelycosaurs
• Two well known pelycosaurs, which
evolved their sails independently were the
carnivorous Dimetrodon, and the planteating Edaphosaurus.
• Dimetrodon has a larger skull and teeth
than does Edaphosaurus, suggesting that
Dimetrodon was a meat-eater.
Therapsids
Therapsids were small to moderate-sized animals
with mammalian skeletal characteristics:
1. Fewer bones in the skull than the other
reptiles
2. Mammal-like structure of the jaw
3. Differentiated teeth (incisors, canines, and
cheek teeth)
4. Limbs in more direct alignment beneath the
body
5. Reduction of ribs in the neck and lumbar
regions, allowing greater flexibility
Therapsids
6. Double ball-and-socket joint between the skull
and neck
7. Bony palate which permitted breathing while
chewing (an important characteristic for
animals evolving toward mammalian warmbloodedness). Efficient breathing provides
oxygen needed to derive heat energy from
food.
8. Whisker pits on the snout.
Geologic range: Permian to Triassic.
Therapsids - Cynognathus
• Mammal-like features are well developed in the
therapsid, Cynognathus.
• Name: From "kynos" meaning "dog" and
"gnathos" meaning "jaw" or "tooth".
Cynognathus crateronotus, a
therapsid from the Early Triassic
(230-225 m.y.), Cape Province,
South Africa.
Note the differentiated teeth. This
animal was a predator.
Therapsids - Cynognathus
• Examination of the bone on the snout portion of
the skull reveals probable "whisker pits",
suggesting that they had hair, which may have
functioned to insulate the animal and slow the
rate of heat loss.
Cynognathus crateronotus, a
therapsid from the Early Triassic
(230-225 m.y.), Cape Province,
South Africa.
Note the differentiated teeth. This
animal was a predator.
Plants of the Paleozoic
Stromatolites - A Photosynthetic
Plant Ancestor
• The earliest photosynthetic organisms were in
the sea.
• Stromatolites, built by photosynthetic bacteria
(cyanobacteria, sometimes called blue-green
algae), were ancestral to the Paleozoic plants.
They were not plants themselves.
• Kingdom Eubacteria.
Stromatolites growing in
the intertidal zone of
Shark Bay, western
Australia
Stromatolites - A Photosynthetic
Plant Ancestor
• Stromatolites:
– Appeared in the Archean
– Expanded during the Proterozoic
– Are present in limestones of the Phanerozoic.
• Most Precambrian stromatolites grew in shallow
marine and intertidal environments, but some
lived in freshwater.
Stromatolites - A Photosynthetic
Plant Ancestor
• Stromatolite reefs were widespread during
the Cambrian, but declined in the
Ordovician. They are typically found in
areas lacking marine invertebrates, which
feed on the cyanobacterial mats.
• The appearance of abundant marine
invertebrates in the Cambrian led to the
decline of the stromatolites. Why? They
ate them.
Marine Algae
•
•
•
The next step in the evolutionary path to
land plants was probably the green algae
or chlorophytes. Kingdom Protista.
Marine algae fossils are found in some
Paleozoic rocks.
Types of marine algae:
1. Chlorophytes
2. Receptaculitids
Chlorophytes
1. Chlorophytes - Green algae.
• Cambrian to Recent.
• A close relationship between chlorophytes
and land plants is suggested by the
adaptation of some species to freshwater
and moist soil.
Receptaculitids
2. Receptaculitids are lower Paleozoic
marine fossils resembling sunflowers.
– Produced by organisms of uncertain affinity.
– Interpreted as lime-secreting algae.
– Most are found in the Ordovician, but they
are also present in the Silurian and
Devonian.
Land Plants
Land plants include:
1. Bryophytes - non-vascular plants
Mosses, liverworts, and hornworts.
Devonian to Recent.
2. Tracheophytes - vascular plants
Trees, ferns, and flowering plants.
Silurian to Recent
Tracheophytes
• Tracheophytes have vascular tissues, or
an internal system of tubes and vessels,
that transport water and nutrients from one
part of the plant to another.
• A water transport system is important,
because plants generally withdraw water
from below the ground. Below the ground
there is water but no light. Above the
ground there is sunlight but there may not
be water. The vascular system allows the
plant to take advantage of both places.
Tracheophytes
• The oldest unquestioned vascular plant fossils
occur in Silurian rocks.
• Small, leafless plants with thin branching stems.
• These plants are called psilophytes.
• Spore bodies are present on the ends of the
stems in fossils of Cooksonia.
Cooksonia, an early vascular
plant in the Late Silurian - Early
Devonian. Height about 4 cm.
Major Advances in Land Plants
Three major advances in land plant history,
developing more efficient reproductive systems:
1. Seedless spore-bearing plants, appearing in the
Ordovician, and flourishing in Carboniferous coal
swamps
2. Seed-producing, pollinating, but non-flowering
plants appearing in the Late Devonian
(gymnosperms, such as conifers)
3. Flowering plants, appearing in the Late Mesozoic
(angiosperms)
Spore-bearing Plants
• The first plants to invade the land were
spore-bearing plants.
• In fact, the first evidence of land plants is
the presence of spores in Ordovician
rocks.
• Spores are plant reproductive structures.
Familiar spore-bearing plants include
mosses and ferns.
Life Cycle of Spore-bearing
Plants
• The life cycle of spore-bearing plants
differs from that of the more familiar seedbearing plants.
• Alternation of generations between diploid
(double set of chromosomes) and haploid
(single set of chromosomes) forms.
• Water is required for fertilization.
The First Seeds
• Seeds appeared in the Late Devonian, although
it is not known which plant produced them.
• Seed-bearing plants became more abundant in
the Carboniferous.
• The seed is significant because it freed plants
from their dependence on moist environments
and allowed them to inhabit dry land, much as
the amniotic egg freed animals from their
dependence on wet environments.
Invasion of the Land by Plants
The invasion of the land by plants
profoundly altered the landscape.
– Plant roots slowed erosion.
– Decaying vegetation led to soil formation.
– Plants also provided a food source for
animals, which invaded the land after the
appearance of land plants. Animals could not
have survived on land without a food source
(plants) in place.
Evolution of Wood
• As plants evolved wood,
they were able to withstand
the pull of gravity and grow
taller.
• During the Middle
Devonian, the first wood
appeared in plants of the
genus Rhynia.
Rhynia, a middle
Devonian vascular land
plant with woody
tissues called xylem.
The First Trees
• The first trees were present by the Late
Devonian.
• By the Carboniferous, trees reached 30 m
tall or more, with trunks 1 m in diameter.
Carboniferous Coal
• There are more plant fossils in Carboniferous
strata than in any other geologic interval.
• Plants gave the Carboniferous its name,
because of the vast coal deposits which formed
from plant remains in lowland swamps. Coal is
dominated by the element carbon.
• Coal represents an enormous biomass of plants
because it takes several cubic meters of wood to
make one cubic meter of coal.
Common plants in the
Carboniferous
1.
2.
3.
4.
Lycopods or Lycopsids - club mosses
Sphenopsids - horsetails, scouring rushes
Ferns
Gymnosperms
a.
b.
c.
d.
Seed ferns
Cordaites
Conifers
Ginkgoes
Lycopods or Lycopsids
• Phylum Lycopodophyta or
Lycopsida
• Club mosses, scale trees
• Spore-bearing plants were
confined to swamps because
spores require moisture to germinate.
• Some grew to be 30 m tall and 1 m diameter.
• Geologic range: Silurian to Recent. Few after the
Permian.
• Common genera = Lepidodendron and
Sigillaria.
Sphenopsids
• Phylum Equisetaphyta or Sphenopsida
• Spore-bearing and similar to living
horsetails or scouring rushes.
• Interpreted as living in moist areas or standing
water.
• Geologic range: Devonian to Recent.
Few after the Permian.
• Common genus = Calamites
Ferns
• Phylum Polypodiophyta
• Ferns are vascular plants that reproduce
by means of spores.
• They live in moist habitats.
• Geologic range: Devonian to Recent.
Gymnosperms
• Phylum Pinophyta or Gymnospermophyta
• Conifers, cycads, ginkgoes, and various
evergreen plants without flowers
• The word "gymnosperm" means "naked seed".
• Seed-bearing plants. No flowers.
• Seed-bearing plants no longer require moist
habitats. This led to the expansion of plants into
drier areas.
• Geologic range: Middle Paleozoic to Recent.
Seed ferns
• Gymnosperms. Class Pteridospermophyta
• Fernlike leaves, but reproduced with seeds instead
of spores.
• Geologic range: Devonian to Recent.
• Common genera = Neuropteris and Glossopteris.
• One of the best-known is Glossopteris, which lived
in Gondwana during the Carboniferous and
Permian. They were sometimes associated with
glacial deposits, suggesting that they were adapted
to cool climates.
Cordaites
• Gymnosperms. Class Pinopsida,
Order Cordaitales
• Seed-bearing gymnosperms with strap-like
leaves that were ancestors to the modern
conifers.
• Tall trees (up to 50 m).
• Abundant in Carboniferous coal swamps.
• Extinct by the end of the Permian.
Conifers
• Gymnosperms. Class Pinopsida, Order
Coniferales
• The word "conifer" means "cone bearing".
• Trees with cones which contain seeds.
• Today conifers are represented by trees such as
pines, cedars, hemlocks, spruces, firs, etc.
• Conifers spread widely during the Permian,
perhaps as a result of the drier conditions which
led to the demise of the coal swamps.
Ginkgoes
•
•
•
•
•
Gymnosperms. Class Ginkgopsida
Deciduous trees (they drop their leaves)
Fan-shaped leaves.
They produce a fleshy fruit but have no flowers.
Geologic range: Early Permian to Recent.
Maximum diversity in the Jurassic.
• Represented by a single species today, Ginkgo
biloba. It is extinct in the wild, but is widely
grown as an ornamental tree.
Mass Extinctions in the Paleozoic
• The Paleozoic was a time of adaptive
radiations and extinctions.
• Many of the geologic periods of the
Paleozoic began with adaptive radiations,
or times of rapid evolution of organisms.
Several of the Paleozoic periods ended
with extinction events of varying severity.
Mass Extinctions in the Paleozoic
The three most catastrophic extinctions in the
Paleozoic Era were at the following times:
– End of the Ordovician Period (443 m.y. ago)
– End of the Devonian Period (359 m.y. ago)
– End of the Permian Period (251 m.y. ago)
The Permian extinction was the most severe.
The extinction at the end of the Permian Period is
considered to be the most catastrophic mass
extinction in the history of life.
Diversity of marine animals, and extinction events
over geologic time.
Late Ordovician Extinctions
• Following a slight dip in diversity at the end of
the Cambrian, the Ordovician was a time of
renewed diversification. The number of genera
increased rapidly, and the number of families
increased from about 160 to 530. This increase
was particularly dramatic among trilobites,
brachiopods, bivalved molluscs, and gastropods.
• An extinction event at the end of the
Ordovician led to an abrupt decline in diversity.
Late Ordovician Extinctions
• The extinction occurred in two phases.
– First phase - affected planktonic and nektonic
(floating and swimming) organisms such as
graptolites, acritarchs, many nautiloids and
conodonts, as well as benthic (bottomdwelling) organisms such as trilobites,
bryozoa, corals, and brachiopods.
– Second phase - affected several trilobite
groups, corals, conodonts, and bryozoans.
Late Ordovician Extinctions
• Both phases of the extinction event were related
to global cooling and the growth of glaciers in
Gondwana.
• Glaciation was coupled with the lowering of sea
level and a reduction in shallow water habitat.
• As the climate cooled, tropical organisms
showed the greatest decline.
• As warming occurred and the glaciers began to
melt, organisms which were adapted to the
cooler conditions began to suffer extinction. This
was the second phase of extinctions.
Late Devonian Extinctions
The Late Devonian extinctions occurred
over a span of about 20 million years, and
appear to have been the result of an
ecological crisis in the seas, perhaps
induced by changes occurring on the land.
Late Devonian Extinctions
• The Devonian was the time of the appearance of
trees and spread of land plants. This would have
accelerated weathering rates, leading to large
volumes of nutrients being washed into the seas.
• Large quantities of nutrients in the water (such
as phosphorus) causes algal blooms.
• Bacteria breaking down large quantities of dead
algae uses up all of the oxygen in the water,
causing anoxic conditions (= "without oxygen").
• This process is called eutrophication, and it
occurs today in lakes, and causes massive "fish
kills".
Late Devonian Extinctions
• Extensive Devonian black shale deposits (for
example, the Chattanooga Shale) suggest the
widespread occurrence of anoxic conditions in
the Devonian sea.
• Glaciation may have been an additional
contributing factor. By the Late Devonian, South
America had drifted over the South Pole, and
glaciations occurred.
• Overall, 70% of marine invertebrate families
went extinct in the Late Devonian.
Late Devonian Extinctions
Organisms most strongly affected (but not totally
wiped out) by the Devonian extinction were:
– Tabulate corals
– Rugose corals
– Stromatoporoids
– Brachiopods
– Goniatite ammonoids (cephalopod molluscs)
– Trilobites
– Conodonts
– Placoderm fish
Late Permian Extinctions
• The Late Permian is marked by a
catastrophic extinction event which
resulted in the total disappearance of
many animal groups.
• This was the largest extinction event in the
history of life, exceeding even the
extinction event at the end of the
Cretaceous, which killed the dinosaurs.
Late Permian Extinctions
• More than 90% of all marine species that
existed in the Permian disappeared or
were severely reduced in number.
• Nearly half of the known families
disappeared.
• Tropical forms experienced the most
extensive losses.
Late Permian Extinctions
• The following marine organisms were
extinct by the end of the Permian:
– Fusulinid foraminifera
– Rugose corals
– Tabulate corals
– Blastoids
– Trilobites (which had become extinct
somewhat earlier in the Permian)
Late Permian Extinctions
• Other groups of organisms were severely
reduced in diversity, with some surviving
species:
– Brachiopods
– Crinoids
– Bryozoa
– Ammonoids
• Organisms which inhabited warm waters shifted
their distributions toward the equator. Cool
conditions prevented construction of reefs and
the formation of limestones.
Late Permian Extinctions
• The Permian extinction also affected land
dwellers.
• More than 70% of land animals
disappeared or were severely reduced,
including:
– Amphibian families
– Reptile families
– Synapsids (once called "mammal-like reptiles")
Late Permian Extinctions
• Among the plants, the spore-bearing
plants that inhabited tropical coal swamps
were replaced by seed-bearing
gymnosperms, that could inhabit cooler,
drier climatic conditions.
Contributing Factors
Many factors may have contributed to the Permian
mass extinction:
1. Climatic change associated with assembly of
Pangea –
Global cooling and drying, along with
interruption of equatorial circulation
2. Glaciation at both north and south ends of
Pangea
3. Reduction in epicontinental seas as sea level
dropped (habitat loss)
Contributing Factors
4. Unusually active volcanism releasing CO2
(flood basalts in Siberia), leading to global
warming, which may have triggered release of
large stores of methane gas frozen in
sediments on the sea floor, causing increased
global warming.
5. Possibility of an extraterrestrial impact, as
indicated by spherical carbon molecules
containing an extraterrestrial helium-3 isotope