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Topic 4: The Origin of Tetrapods
Next two lectures will deal with:
Origin of Tetrapods, transition from
water to land.
Origin of Amniotes, transition to dry
habitats.
The geological time scale
Organizes the history of the earth
Based on geological and biological/fossil criteria
Allows us to consider “________________”
Time scale over which geological and
___________________ phenomena occur
Organized into hierarchical ________, ________,
______________, and ______________
The Paleozoic Era
Period
Permian
245-286
286-320
Devonian
360-408
Silurian
408-438
Ordovician
Cambrian
438-505
505-570
What is the geological time scale and why
is it important?
Where do herps fit in the vertebrate
phylogeny?
What are the evolutionary origins of
tetrapods?
What changes were involved in the
transition from water to land?
The geological time scale
Eon
Era
MYA
Cenozoic
0-65
Mesozoic
65-245
Paleozoic
245-570
Proterozoic
570-2500
Phanerozoic
Precambrian
Precambrian
accounts for
~88% of Earth
history
We will
concentrate on
Phanerozoic
1st multicellular
organisms
Archaen
2500-3800 1st unicellular organisms
Hadean
3800-4600
Age of oldest rocks
The Mesozoic Era
MYA
Carboniferous
Topic 4: The Origin of Tetrapods
Events
Period
MYA
Events
65-144
- Mass extinction at end of
Cretaceous
- 1st modern Squamata
1st _________________
Cretaceous
1st reptiles, amphibians
specialize
- 1st Urodela, Anura
- 1st Rynchocephalia
- High reptile diversity
- 1st birds
1st amphibians
1st jawed fishes
1st
Jurassic
144-208
Triassic
208-245
jawless fishes &
land plants
1st vertebrates
-1st
- 1st
Angiosperms, dinosaurs,
mammals
Testudines, ___________
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The Cenozoic Era
Period
What are stem and crown groups?
Epoch
MYA
Holocene
Recent
Quanternary
Pleistocene 0.01-1.5
Tertiary
Pliocene
1.5-5
Miocene
5-24
Oligocene
24-37
Eocene
37-58
Paleocene
58-65
Comments
Crown groups:
Are monophyletic
Contain all extant taxa
Can contain extinct taxa
_________________ – contains crown
group plus closely related extinct taxa.
Last common ancestor is older than that
for its extant members
1st hominines
-1st Gymnophiona
- 1st pacental mammals
Stem groups:
_________________ – smallest
monophyletic group to contain the last
common ancestor of all extant members
of a taxon
Evolution of humans
What are stem and crown groups?
Modern humans
Where do herps fit into the
vertebrate phylogeny?
Are also monophyletic
Contain all extant &
extinct taxa
Phylogeny of jawed
vertebrates
What are outgroups of
Tetrapoda (3)?
Actinopterygii (6)
Actinistia (7)
Dipnoi (8)
____________________ (6)
are ray-finned fishes
Extremely diverse (~25,000
spp.)
Highly derived
Fins have extrinsic muscle
Pough et al 2004, Fig 2-1
Benton Fig 9.11
Where do herps fit into the
vertebrate phylogeny?
Sarcopterygian lineages
________________ (2)
Lobe-finned fishes
Contain Actinistia (7),
Dipnoi (8), Tetrapoda
(3)
_________________
Fins/limbs are
supported by bone and
contain ___________
muscle
Teeth have enamel
Pough et al 2004, Fig 2-1
Benton Fig 9.11
_________________
What kind of characters
are these?
Coelacanth, Latimeria
2 extant species
Symmetrical, 3-lobed
________
“living fossil”
Lung fishes
3 extant genera
Gondwanan distribution
1 in S. America, 1 in
Africa, 1 in Australia
Vertebrate Life Fig 8-35
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Sarcopterygian lineages
Tetrapoda
Includes all modern
amphibians and
amniotes, and their
last common ancestor.
_________________
_________________
Fully developed
_____________ girdle
Pectoral girdle free
from the skull (not the
case in non-tetrapods)
Discrete shaft of
______________
Where do herps fit into the
vertebrate phylogeny?
This phylogeny includes
only extant taxa
Many species of early
tetrapods and
stegocephalians are
extinct
Therefore, must look at
both stem and crown
Amphibia
Pough et al 2004, Fig 2-1
Stem and Crown Amphibia
Most groups of
Amphibians and all
early tetrapods are
____________
Benton 1997, Fig 4-21
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Early tetrapod relationships are contentious
How do these two hypotheses differ? How are they the same?
Why might we prefer one over the other?
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
Laurin & Reisz 1997
Traditional hypothesis
Inclusion of only some taxa, assumption of
Temnospondyl-Lissamphibian association
No a priori assumptions,
many more taxa included
Pough et al. 2004 Fig 2-8
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What are the evolutionary origins of tetrapods?
What are the evolutionary origins of tetrapods?
Elpistostegidae (Panderichthys)
Laurin & Reisz 1997
Lepospondyls are:
__________________
Sister to Lissamphibia
Amniotes (including reptiles) are:
Sister group to
Lissamphibia+Lepospondyls
Outgroup to Stegocephalia but
closer than Dipnoi
Dorsoventrally _____________,
no dorsal fin, dorsal eyes
_________________ water
Tetrapod-like body but with fins
Developed frontal bones a
synapomorphy with
stegocephalia
Stegocephali
Tetrapoda
Lepospondyls
Pough et al. 2004 Fig 2-8
Temnospondyls
What are the evolutionary origins of tetrapods?
Stegocephali Lepospondyls
Tetrapoda
Temnospondyls
___________ from Devonian
(360mya) of Greenland and
Russia
Four limbs with digits, but also a
branchial apparatus with gills ________________
Pough et al. 2004 Fig 2-2
What are the evolutionary origins of tetrapods?
Acanthostega & Ichthyostega
Stegocephali Lepospondyls
Tetrapoda
Temnospondyls
Vertebrate Life Fig 10-3
What are the evolutionary origins of tetrapods?
Carboniferous
Few centimeters to over 1m
Limbed, posture more upright
than Acanthostega/Ichthyostega
Some aquatic, others (below)
terrestrial
Typically ________________
Pough et al. 2004 Fig 2-7
6-8 digits per limb
What does this mean for
ancestral number of digits?
Amniota
Stegocephali Lepospondyls
Tetrapoda
Temnospondyls
_______________
Temnospondyls
Pough et al. 2004 Fig 2-3
What are the evolutionary origins of tetrapods?
Acanthostega & Ichthyostega
Stegocephali Lepospondyls
Tetrapoda
Temnospondyls
We will come back to these
Mammals, birds, snakes &
lizards, turtles, crocidilians
Next slide
Stegocephali Lepospondyls
Tetrapoda
Temnospondyls
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What are the evolutionary origins of tetrapods?
What are the evolutionary origins of tetrapods?
Lepospondyls
Carboniferous & Permian
Diverse
Microsauria – _________
& small
Aisopoda – ___________
Nectridea – _________ &
newt-like
Pough et al. 2004 Fig 2-4b,c; 4-14, 4-15
What changes were involved in the transition
from water to land?
Obligate Aquatic
What is involved in
this major
evolutionary
transition?
Stegocephali Lepospondyls
Tetrapoda
Temnospondyls
Urodela, Anura, Gymnophiona
Extant (finally)
Photos: KP Bergmann, Pough et al. Fig 3-8
What changes were involved in the
transition from water to land?
This transition involved aspects
of structure and function
associated with:
Terrestrial
Lissamphibia
____________________
____________________
____________________
____________________
____________________
____________________
____________________
____________________
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What changes were involved in the
transition from water to land?
What changes were involved in the
transition from water to land?
Body support
Moving onto land means coping
with _____________
In the water, the body is
supported by the water, on
land by limbs
Coping with ______________
__________________
Ground reaction forces
Actinopterygii
Pectoral girdle became
____________ from the head
Minimizes forces exerted on
skull and brain, increases head
____________
Small in water
Large on land
Ichthyostega
Panderichthys
Benton 1997 pg 183; Benton Fig 4-2a; Pough et al 2004 Fig 2-2
What changes were involved in the
transition from water to land?
What changes were involved in the
transition from water to land?
Ground reaction forces
Limb girdles became more ______________ to the
vertebral column
Allows limbs to become support structures and transfer
forces to the axis
Locomotion
Protopterus
(African lungfish)
A switch from ____________
to walking and running
Terrestrial locomotion is much
harder on the ___________
Fin-based swimming is
replaced by pushing off a
substrate with the limbs
Lateral undulation plays a role
in both
________________ less of an
issue on land
Acanthostega
Benton 1997 Fig 3.22; Pough et al 2004 Fig 2-2a
What changes were involved in the
transition from water to land?
Locomotion
Locomotion
Limbs change dramatically:
More ____________
More ________________
Switch from extrinsic to
intrinsic limb musculature
Panderichthys & Acanthostega
What changes were involved in the
transition from water to land?
Vertebral morphology becomes more ______________
Zygapophyses limit excessive intervertebral forces,
especially _____________
Acanthostega
Vertebrate Life Fig 10-3
Kardong & Zalisko 2002: Fig 5.8c, 5.11b
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What changes were involved in the
transition from water to land?
What changes were involved in the
transition from water to land?
Body shape
Very _________________ in fishes
Streamline but dorsoventrally
flattened in Panderichthys
Allows invasion of shallow
water
Also dorsal eyes, no dorsal fin
Decrease in hydrodynamics in
terrestrial forms
What changes were involved in the
transition from water to land?
Trend from excreting ammonia
to __________ to ___________
Ammonia is most toxic but also
most water soluble
Both gills and lungs are
ancestral because lungs
arose from ____________
Acanthostega still had gills
Ventilation increasingly
powered by __________ of
the ______________
Water balance
Lissamphibia live in moist
environments, but more water_________________
Ammonia is voided quickly
through ___________
Mucous glands limit evaporation
from an amphibian’s body
Urea and Uric Acid are
concentrated and excreted by
_______________
Lissamphibia have various
behaviors and postures that limit
water loss
Sound travels differently in air than in water
Other organisms are similar density to water
In air there is a differential between densities
Hyomandibula bone of the 1st gill arch gives rise to the
_______________, an inner ear bone that connects to
the ____________________
This allows for better conduction of vibrations to the inner
ear
Kardong & Zalisko Fig 5.29d
Fishes live in excess water
Hearing
Gills only to gills & lungs to
lungs only
What changes were involved in the
transition from water to land?
What changes were involved in the
transition from water to land?
Excretion
Respiration
What changes were involved in the
transition from water to land?
Feeding
______________ is prevalent in fishes, impossible on land
On land, jaws and the tongue play a more important role
Pough et al 2004, Fig 11-19
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