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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.
Topic 4: The Origin of Tetrapods
� 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
� 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 geological time scale
Eon Era
Phanerozoic
Cenozoic
Mesozoic
Paleozoic
Precambrian
Proterozoic
Archaen
Hadean
MYA
0-65
65-245
245-570
570-2500
2500-3800
3800-4600
� Precambrian accounts for ~88% of Earth history
� We will concentrate on Phanerozoic
Age of oldest rocks
1st unicellular organisms
1st multicellular organisms
1st multicellular organisms
Age of oldest rocks
1st multicellular organisms
Age of oldest rocks
The Paleozoic Era
Period
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
MYA
245-286
286-320
360-408
408-438
438-505
505-570
Events
1st _________________
1st reptiles, amphibians specialize
1st amphibians
1st jawed fishes
1st jawless fishes & land plants
1st vertebrates
The Mesozoic Era
Period
Cretaceous
Jurassic
Triassic
MYA
65-144
144-208
208-245
Events
- Mass extinction at end of Cretaceous
- 1st modern Squamata
- 1st Urodela, Anura
- 1st Rynchocephalia
- High reptile diversity
- 1st birds
-1st Angiosperms, dinosaurs, mammals
- 1st Testudines, ___________
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The Cenozoic Era
Period Epoch
QuanternaryHolocene
Pleistocene
Tertiary
Pliocene
Miocene
Oligocene
Eocene
Paleocene
MYA
Recent
0.01-1.5
1.5-5
5-24
24-37
37-58
58-65
Comments
Modern humans
Evolution of humans
1st hominines
-1st Gymnophiona
- 1st pacental mammals
What are stem and crown groups?
� _________________ – smallest monophyletic group to contain the last common ancestor of all extant members of a taxon
� _________________ – contains crown group plus closely related extinct taxa. Last common ancestor is older than that for its extant members
What are stem and crown groups?
� Crown groups:
� Are monophyletic
� Contain all extant taxa
� Can contain extinct taxa
Benton Fig 9.11
� Stem groups:
� Are also monophyletic
� Contain all extant & extinct taxa
Where do herps fit into the
vertebrate phylogeny?
� 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
� ________________ (2)
� Lobe-finned fishes
� Contain Actinistia (7), Dipnoi (8), Tetrapoda (3)
� Fins/limbs are supported by bone and contain ___________ muscle
� Teeth have enamel
� What kind of characters are these?
Pough et al 2004, Fig 2-1
Where do herps fit into the
vertebrate phylogeny? Sarcopterygian lineages
Benton Fig 9.11
Vertebrate Life Fig 8-35
� _________________
� 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
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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 ______________
� 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
Where do herps fit into the
vertebrate phylogeny?
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�
Pough et al. 2004 Fig 2-8
Traditional hypothesis
Laurin & Reisz 1997
Inclusion of only some taxa, assumption of Temnospondyl-Lissamphibian association
No a priori assumptions, many more taxa included
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
How do these two hypotheses differ? How are they the same? Why might we prefer one over the other?
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What are the evolutionary origins of tetrapods?
Pough et al. 2004 Fig 2-8
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
� Laurin & Reisz 1997
� Lepospondyls are:
� __________________
� Sister to Lissamphibia
� Amniotes (including reptiles) are:
� Sister group to Lissamphibia+Lepospondyls
Pough et al. 2004 Fig 2-3
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
� Elpistostegidae (Panderichthys)
� 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
What are the evolutionary origins of tetrapods?
Pough et al. 2004 Fig 2-2
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
� Acanthostega & Ichthyostega
� ___________ from Devonian (360mya) of Greenland and Russia
� Four limbs with digits, but also a branchial apparatus with gills �________________
What are the evolutionary origins of tetrapods?
Vertebrate Life Fig 10-3
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
� Acanthostega & Ichthyostega
� _______________
� 6-8 digits per limb
� What does this mean for ancestral number of digits?
What are the evolutionary origins of tetrapods?
Pough et al. 2004 Fig 2-7
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
� Temnospondyls
� Carboniferous
� Few centimeters to over 1m
� Limbed, posture more upright than Acanthostega/Ichthyostega
� Some aquatic, others (below) terrestrial
� Typically ________________
What are the evolutionary origins of tetrapods?
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
� Amniota
� We will come back to these
� Mammals, birds, snakes & lizards, turtles, crocidilians
What are the evolutionary origins of tetrapods?
� Next slide
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Pough et al. 2004 Fig 2-4b,c; 4-14, 4-15
� Lepospondyls� Carboniferous & Permian
� Diverse� Microsauria – _________ & small
� Aisopoda – ___________� Nectridea – _________ & newt-like
What are the evolutionary origins of tetrapods?
Photos: KP Bergmann, Pough et al. Fig 3-8
Stegocephali
Tetrapoda
Lepospondyls
Temnospondyls
� Lissamphibia
� Urodela, Anura, Gymnophiona
� Extant (finally)
What are the evolutionary origins of tetrapods?
What changes were involved in the transition
from water to land?
What is involved in
this major evolutionary
transition?
Terrestrial
Obligate Aquatic� This transition involved aspects
of structure and function associated with:
� ____________________
� ____________________
� ____________________
� ____________________
� ____________________
� ____________________
� ____________________
� ____________________
What changes were involved in the
transition from water to land?
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� Body support� Moving onto land means coping
with _____________
� In the water, the body is supported by the water, on land by limbs
� Coping with ______________ __________________
� Small in water
� Large on land
What changes were involved in the
transition from water to land?
� Ground reaction forces
� Pectoral girdle became ____________ from the head
� Minimizes forces exerted on skull and brain, increases head ____________
Ichthyostega
Benton 1997 pg 183; Benton Fig 4-2a; Pough et al 2004 Fig 2-2
Panderichthys
Actinopterygii
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
Benton 1997 Fig 3.22; Pough et al 2004 Fig 2-2a
Acanthostega
Protopterus(African lungfish)
What changes were involved in the
transition from water to land?
� Locomotion
� 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
What changes were involved in the
transition from water to land?
� Locomotion
� Limbs change dramatically:
� More ____________
� More ________________
� Switch from extrinsic to
intrinsic limb musculature
AcanthostegaPanderichthys & Acanthostega
Vertebrate Life Fig 10-3
What changes were involved in the
transition from water to land?
� Locomotion
� Vertebral morphology becomes more ______________
� Zygapophyses limit excessive intervertebral forces, especially _____________
Kardong & Zalisko 2002: Fig 5.8c, 5.11b
What changes were involved in the
transition from water to land?
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� 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?
� Respiration� Gills only to gills & lungs to
lungs only
� Both gills and lungs are ancestral because lungs arose from ____________
� Acanthostega still had gills
� Ventilation increasingly powered by __________ of the ______________
What changes were involved in the
transition from water to land?
� Excretion
� Trend from excreting ammonia to __________ to ___________
� Ammonia is most toxic but also most water soluble
� Ammonia is voided quickly through ___________
� Urea and Uric Acid are concentrated and excreted by _______________
What changes were involved in the
transition from water to land?
� Water balance
� Fishes live in excess water
� Lissamphibia live in moist environments, but more water-_________________
� Mucous glands limit evaporation from an amphibian’s body
� Lissamphibia have various behaviors and postures that limit water loss
What changes were involved in the
transition from water to land?
� Hearing
� 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
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
What changes were involved in the
transition from water to land?