Tetrapod Footprint Discovery
• The discovery in 1992 of fossilized Devonian
tetrapod footprints
– more than 365 million years old
– has forced paleontologists to rethink
– how and when animals emerged onto land
GEOLOGY IS A YOUNG SCIENCE, CONSTANTLY
EVOLVING WITH RICH NEW DISCOVERIES
JUST WAITING FOR THE NEXT CLASS OF GRADUATE
GEOLOGISTS TO “ROCK THE WORLD”
Tetrapod Footprint Discovery
• Tetrapod trackway
– at Valentia Island,
Ireland
• These fossilized
footprints
– which are more
than 365 million
years old
– are evidence of
one of the earliest
four-legged
animals on land
Transition from Water to Land
• One of the striking parallels between plants
and animals
– is the fact that in passing from water to land,
– both plants and animals had to solve the same
basic problems
• For both groups,
– reproduction was the major barrier
• With the evolution of the seed in plants and
the amniote egg in animals,
– this limitation was removed, and both groups were
able to expand into all the terrestrial habitats
Vertebrate Evolution
• A chordate (Phylum Chordata) is an animal
that has, at least during part of its life cycle,
– a notochord,
– a dorsal hollow nerve cord,
– and gill slits
• Vertebrates, which are animals with
backbones, are simply a subphylum of
chordates
Characteristics of Chordates
• The structure of the lancelet Amphioxus
illustrates the three characteristics of a
chordate:
– a notochord, a dorsal hollow nerve cord, and gill
slits
A Very Old Chordate
• Yunnanozoon lividum is one of the oldest known
chordates
– Found in 525 MY old rocks in Yunnan province, China
– 5 cm-long
animal
Sturgeon
Fresh water fish Canada
A prehistoric fish
Has a notochord,
No scales, plates instead
Asymetrical tail
Hypothesis for Chordate Origin
– a random mutation produced a duplicate set of
genes
– allowing the ancestral vertebrate animal to evolve
entirely new body structures
– that proved to be evolutionarily advantageous
• Not all scientists accept this hypothesis and the
evolution of vertebrates is still hotly debated
Spiral Versus Radial Cleavage
• Echinoderms
and chordates
– have similar
– embryonic
development
• In the arrangement
of cells resulting
from spiral
cleavage, (a) at the left,
– cells in successive rows are nested between each other
• In the arrangement of cells resulting from radial
cleavage, (b) at the right,
– cells in successive rows are directly above each other
– This arrangement exists in both chordates and echinoderms
Fragment of Primitive Fish
Fish appear in the late Cambrian
• A fragment of a plate from Anatolepis cf. A.
heintzi from the Upper Cambrian marine
Deadwood Formation of Wyoming
• Anatolepis is one of the oldest known fish
– a primitive member of the class Agnatha (jawless
fish)
Ostracoderms —
“Bony Skinned” Fish
• The oldest and most primitive of the class
Agnatha are the ostracoderms
– whose name means “bony skin”
• These are armored jawless fish that first
evolved during the Late Cambrian
– reached their zenith during the Silurian and
Devonian
– and then became extinct
ostracoderm
An ostracoderm, an extinct jawless fish that existed from about
510 million to 350 million years ago. The name means "shellskinned," and this fish was typically armored with scales and
bony plates. Instead of vertebrae it had a rigid notochord.
(Copyright 1995 by Grolier Electronic Publishing, Inc
Jawless Fish
Modern:
Lamprey
“Living Fossil”
Evolution of Jaws
• The evolution of jaws: advantage
• While their jawless ancestors
– could only feed on detritus
• jawed fish
– could chew food and become active predators
– thus opening many new ecological niches
Apparent modification of the first two or
three anterior gill arches
Devonian: Age of Fish
• Many fish evolved during the Devonian Period
including
– the abundant acanthodians
– placoderms,
– ostracoderms,
– and other fish groups,
• such as the cartilaginous and bony fish
• It is small wonder, then, that the Devonian is
informally called the “Age of Fish”
– because all major fish groups were present during
this time period
Other Jawed Fish
• Devonian jawed fish
– that evolved during the Late Silurian were the
placoderms,
• whose name means “plate-skinned”
• Placoderms were heavily armored jawed fish
– that lived in both freshwater and the ocean,
– and like the acanthodians,
– reached their peak of abundance and diversity
during the Devonian
Devonian Seafloor
• Recreation of a Devonian seafloor showing:
an acanthodian
(Parexus)
a ray-finned fish
(Cheirolepis)
– a placoderm (Bothriolepis)
an ostracoderm (Hemicyclaspis)
Late Devonian Marine Scene
• A Late Devonian marine scene from the
midcontinent of North America featuring the
giant placoderm, Dunkleosteus
Geologic Ranges of
Major Fish Groups
Cartilaginous Fish
• Cartilaginous fish,
– class Chrondrichthyes,
– represented today by
• sharks, rays, and skates,
– first evolved during the Middle Devonian
– and by the Late Devonian,
– primitive marine sharks
• such as Cladoselache were quite abundant
Ray-Finned and Lobe-Finned Fish
• Arrangement of fin
bones for
(a) a typical
ray-finned fish
(b) a lobe-finned fish
– Muscles extend
into the fin
– allowing greater
flexibility
Ray-Finned Fish Rapidly
Diversify
• From a modest freshwater beginning during
the Devonian,
– ray-finned fish,
• which include most of the familiar fish
• such as trout, bass, perch, salmon, and tuna,
– rapidly diversified to dominate the Mesozoic and
Cenozoic seas
Living Fossil: Coelacanths
Coelacanths are marine lobe-finned fish
– that evolved during the Middle Devonian
– and were thought to have gone extinct
– at the end of the Cretaceous.
• In 1938, a fisherman caught a coelacanth
– in the deep waters off Madagascar,
– and several dozen more have been caught since
then.
Lungfish Fish
• Lungfish were fairly abundant during the Devonian,
– but today only three freshwater genera exist,
– one each in South America, Africa, and Australia
• Their present-day distribution presumably
– reflects the Mesozoic breakup of Gondwana
• The “lung” is actually a modified swim bladder
– that most fish use for buoyancy in swimming
• In lungfish, this structure absorbs oxygen,
– allowing them to breathe air
– when the lakes or streams in which they live become
stagnant or dry up.
Lungfish Respiration
• When the lakes become stagnant and dry up,
– The lungfish burrow into the sediment to prevent
dehydration
– and breathe through their swim bladder
– until the stream begins flowing or the lake fills with
water
• When the water is well oxygenated,
– however, lungfish rely upon gill respiration
–Transitional form?
Amphibians Evolved from
Crossopterygians
• The crossopterygians are an important group of
lobe-finned fish because amphibians evolved from them
• Some species reaching over 2 m in length,
– were the dominant freshwater predators
• during the Late Paleozoic.
Rhipidistian Crossopterygian and
Eusthenopteron
Fish/Amphibian Comparison
• Similarities between the crossopterygian lobefinned fish and the labyrinthodont amphibians
• Their
skeletons
were similar
Comparison of Limbs
ulna
radius
humerus
• Comparison of the limb bones
– of a crossopterygian (left) and an amphibian (right)
• Color identifies the bones that the two groups
have in common
Water to Land Barriers
• What structural problems
existed for marine
animals to move on to
land?
Acanthostega – oldest tetrapod?
– desiccation
– reproduction
– the effects of gravity – stronger bones required
– and the extraction of oxygen
• from the atmosphere by lungs
rather than from water by gills
• Protection from predators – cover?
Problems Partly Solved
• These problems were already partly solved by the
crossopterygians
– they already had a backbone and limbs
– that could be used for walking
– and lungs that could extract oxygen
• The oldest amphibian fossils are found
– in the Upper Devonian Old Red Sandstone of eastern Greenland
Amphibians—
Vertebrates Invade the Land
• Although amphibians were the first vertebrates to
live on land,
– they were not the first land-living organisms
• Land plants, which probably evolved from green
algae,
– first evolved during the Ordovician
• Furthermore, insects, millipedes, spiders,
– and even snails invaded the land before amphibians
A Late Devonian Landscape
• A Late Devonian Landscape in Eastern
Greenland
• The flora was diverse,
– consisting of a
variety of small and
large seedless
vascular plants
• Ichthyostega was an
amphibian that grew to
a length of about 1 m
Compare tetrapod to amphibian
Early amphibian
Oldest tetrapod
Transition to Amphibians
• In 2006, an exciting discovery
– of a 1.2-2.8 m long
– 374-million-year-old (Late Devonian) “fishapod”
– was announced.
• Tiktaalik roseae (“large fish in a stream”)
– was hailed as an intermediary
– between lobe-finned fish like Panderichthys
– and the earliest tetrapod, Acanthostega.
Tiktaalik roseae
• This “fishapod” has
characteristics of both
fish and tetrapods
– It has gills and fish
scales
– but also a broad skull,
eyes on top of its head,
flexible neck and large
ribcage
– that could support its
body on land or
shallow water,
• and the beginning of a
true tetapod forelimb
Tiktaalik roseae
• Diagram illustrating
how Tiktaalik roseae
is a transitional
species between
lobe-finned fish and
tetrapods
Carboniferous Coal Swamp
• Reconstruction of a Carboniferous coal swamp
Evolution of the Reptiles —
the Land is Conquered
• Amphibians were limited in colonizing the land
– because they had to return to water to lay their
gelatinous eggs
• The evolution of the amniote egg freed
reptiles from this constraint
• In such an egg, the developing embryo
– is surrounded by a liquid-filled sac,
• called the amnion
– and provided with both a yolk, or food sac,
– and an allantois, or waste sac
Amniote Egg
• The amnion cavity
– surrounds the embryo.
• The yolk sac
– provides the food
source
• while the allantois
– serves as a waste sac
• The evolution of the
amniote egg freed
reptiles
– to inhabit all parts of
the land
Colonization of
All Parts of the Land
• In this way the emerging reptile is
– in essence a miniature adult,
– bypassing the need for a larval stage in the water
• The evolution of the amniote egg allowed vertebrates
– to colonize all parts of the land
– because they no longer had to return
– to the water as part of their reproductive cycle
• SUCCESS of reptiles is partly because
– of their advanced method of reproduction
– and their more advanced jaws and teeth,
• as well as their ability to move rapidly on land
Paleozoic Reptile Evolution
• Evolutionary
relationship
among the
Paleozoic
reptiles
Pelycosaurs (Finback Reptiles)
• Most pelycosaurs have a characteristic sail on
their back
The herbivore Edaphosaurus
The carnivore Dimetrodon
Pelycosaurs Sails
• An interesting feature of the pelycosaurs is
their sail
– It was formed by vertebral spines that,
– in life, were covered with skin
• The sail has been variously explained as
– a type of sexual display,
– a means of protection
– and a display to look more ferocious
– OR a thermo-regulatory device! ??
Pelycosaurs Sail Function
• current consensus
– sail served as thermoregulatory device,
– raising the reptile's temperature by catching the
sun's rays or cooling it by facing the wind
• Because pelycosaurs are considered to be the
group from which therapsids evolved, and are
more mammal like
– it is interesting that they may have had some sort
of body-temperature control
Therapsids
• A Late Permian scene in southern Africa
showing various therapsids- 90% of reptiles
– Many paleontologists think therapsids were
endothermic: warm-blooded
– and may have had a covering of fur
– as shown here
Moschops
Dicynodon
Count the losses at the end of the
Permian…….
• By the end of the Permian,
–about 90% of all marine invertebrate species
were extinct,
– compared with more than two-thirds of all
amphibians and reptiles
• Plants apparently did not experience
– as great a turnover as animals did
END HERE
for TEST 3 December 2010
Plant Evolution
• When plants made the transition from water to
land,
– they had to solve most of the same problems that
animals did
• desiccation,
• support,
• and the effects of gravity
• Plants did so by evolving a variety of structural
adaptations that were fundamental to the
subsequent radiations
Major Events in the Evolution of Land Plants
• The Devonian Period was a time of rapid evolution for
land plants
Earliest Land Plants
• The earliest land plants
• from the Middle to Late Ordovician
– were probably small and bryophyte-like in their overall
organization
• but not necessarily related to bryophytes
• The evolution of vascular tissue in plants was an
important step
– as it allowed for the transport of food and water
• The ancestor of terrestrial vascular plants
– was probably some type of green algae
• While no fossil record of the transition
– from green algae to terrestrial vascular plants exists,
– comparison of their physiology reveals a strong link
Vascular Tissue Also Gives
Strength
• Besides the primary function
– of transporting water and nutrients throughout a
plant,
– vascular tissue also provides
– some support for the plant body
• Additional strength that acts to counteract
gravity is derived
– from the organic compounds lignin and cellulose,
– which are found throughout a plant's walls
Earliest Land Plant
Late Silurian and Devonian and found in New York State
• The earliest known
fertile land plant was
Cooksonia
– seen in this fossil from
the Upper Silurian of
South Wales
• produced spores
typical of vascular
plants
• These plants probably
lived in moist
environments such as
mud flats
• This specimen is 1.49
cm long
Parallel between Seedless
Vascular Plants and Amphibians
• An interesting parallel can be seen between seedless
vascular plants and amphibians
• When they made the transition from water to land,
they both required a source of water in order to
reproduce
• Amphibians gelatinous egg had to remain moist
And Plants required water for the sperm to travel through
– to reach the egg
Early Devonian Plants
• Reconstruction of an Early Devonian landscape
– showing some of the earliest land plants
Protolepidodendron\
Dawsonites /
- Bucheria
Late Carboniferous and
Permian Floras
• The rocks of the Pennsylvanian Period
• Late Carboniferous
– are the major source of the world's coal
• Coal results from
– the alteration of plant remains
– accumulating in low swampy areas
• The geologic and geographic conditions of the
Pennsylvanian
– were ideal for the growth of seedless vascular
plants,
– and consequently these coal swamps had a very
diverse flora
Pennsylvanian Coal Swamp
• Reconstruction of a Pennsylvanian coal
swamp
– with its characteristic vegetation
Amphibian Eogyrinus
Horsetail
• Living
sphenopsids
include the
horsetail
Equisetum
Glossopteris
• Another important non-swamp dweller was
Glossopteris, the famous plant so abundant in
Gondwana,
– whose distribution is cited as critical evidence that
the continents have moved through time
Cratonic Sequences of North America
• White areas represent sequences of rocks
• that are
separate
d by
largescale
unconformities
• shown in
brown
Paleogeography of the World
• During the Triassic Period
Early Mesozoic Evaporites
• Evaporites
accumulated in
shallow basins
– as Pangaea
broke apart
during the Early
Mesozoic
– Water from the
Tethys Sea
flowed into the
Central Atlantic
Ocean
Jurassic
Paleogeography of the World
• During the Late Cretaceous Period
Thick Evaporites from the
Southern Ocean
• The subsequent separation of South America
and Africa
– formed a narrow basin
– where thick evaporite deposits
– accumulated from the evaporation
– of southern ocean waters
Thick Southern Ocean Evaporites
• Marine
water
flowed into
the
southern
Atlantic
Ocean
from the
south
Late Cretaceous
note the seaway in central US
Ocean Currents and Continents
• The world's climates result from the complex
interaction between
– wind and ocean currents
– and the location and topography of the continents
• In general, dry climates occur
– on large landmasses
– in areas remote from sources of moisture
– and where barriers to moist air exist,
– such as mountain ranges
• Wet climates occur
– near large bodies of water
– or where winds can carry moist air over land
Evaporites, Red Beds, Dunes, Coal
• Widespread Triassic evaporites, red beds, and
desert dunes: such as Zion National Park
which began in the Jurassic
– in the low and middle latitudes
– of North and South America, Europe, and Africa
– indicate dry climates in those regions,
• while coal deposits
– are found mainly in the high latitudes,
– indicating humid conditions
• These high-latitude coals are analogous to
– today's Scottish peat bog
– or Canadian muskeg
Newark and Hartford Basins form
Widespread igneous intrusions
Areas where
Triassic fault-block
basin deposits
crop out in
eastern North
America
Palisades Sill of the Hudson River
• This sill was one of many that were intruded into the Newark sediments
– during the Late Triassic rifting
– that marked the separation
– of North America from Africa
Reptile Tracks
• Reptile tracks in the Triassic Newark Group
– were uncovered during the excavation
– for a new state building in Hartford,
Connecticut
• Because the tracks were so spectacular,
– the building side was moved
– and the excavation was designated as a state
park
Mesozoic Cephalapods
White Cliffs of Dover, UK
Lived and died in clear warm seas that covered much of Britain around 70 to
100 million years ago. When they died, they fell to the bottom in a rain of
fine white mud. As chalk formed from the mud, layers and lumps of hard,
glassy flint also developed - prized by stone-age man for tools.
Living Fossil
• Latimeria
– belongs to a group of fish once thought to have
gone extinct at the end of the Mesozoic Era
– A specimen was caught off the coast of East Africa
in 1938
– Since then
many more
have been
captured
Reptiles and Birds
All dinosaurs possess
a number of shared characteristics,
such as full and upright posture
with limbs directly beneath their bodies
yet differ enough for us to recognize
two distinct orders,
the Saurischia
and Ornithischia
A distinctive pelvic structure
characterizes each order
Dinosaur Cladogram
• Cladogram showing dinosaur relationships
– showing pelvises of ornithischians and saurischians
– Among the several subgroups of dinosaurs
• theropods were
carnivores
• and all
others were
herbivores