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Lecture 4 Tetrapods I
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Tetrapods are descended from
sarcopterygian fish
KK Fig. 3.20
Sarcopterygian
fish of the kind
thought to be
ancestral to
tetrapods.
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Class Amphibia*
Amphibia, the first tetrapod or land-dwellingvertebrates, appear about 400 mybp. Their ancestorswere Sarcopterygii with lungs and limb-like fins.
early Amphibia lived in the swamp forests that
produced the coal deposits we have so thoroughlydug up, so we know many kinds. There are moreAmphibia known as fossils than as living species.
*Kardong feels that the term Amphibia should only include the modern forms,and not the first land-dwelling vertebrates, but I will use the term in themore general sense.
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Amphibia are not fully terrestrial, as we can see if we list the
adaptation required to move completely away from the water.
Sarcopteryigii Amphibia Reptilia
limbs for walking limited yes yes yes
lungs, external nares yes yes yes
stronger limb girdles
and spine
yes yes
desiccation resistant
skin
few,
somewhat
yes
oral glands yes yes
terrestrial eggs few, recent yes
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Amphibian Classification
Hildebrand and Goslow, 5th
edition:Class Amphibia*
Subclass Icthyosteglia (first, fish-like Amphibia)
Subclass Anthracosauria (ancestors of reptiles)
Subclass Temnospondyli (ancestors of Lissamphibia)
Subclass Lissamphibia(modern Amphibia)
Kardong
Class Labyrinthodontia* (Ichthyostegalia, Anthacosauria and
Temnospondyli)Class Amphibia
Subclass Lepospondyla
Subclass Lissamphibia**terms I will use
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KK Fig. 3.22, 3.23. H&G Fig. 4.1
Examples of the extinct
Amphibians or
labyrinthodonts
Ichthyostegalians were decidedly
fish-like, often with fins on the tail
and numerous digits.
Anthrocosaurs were large, robust
creatures unlike modern Amphibia.
They are named for their highly-
folded labyrinthodont teeth.
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Labyrinthodont Teeth
KK 13.12
Labyrinthodont teeth are highly folded for
strength. They are found in someSarcopterygii (crossopterygians),
labyrinthodonts, and early reptiles.
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Subclass
Lissamphibia
modern Amphibia
Order Urodela, salamanders
Order Anura, frogs and toads
Order Apoda (Gymnophonia)
caecilians
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The Amniotes
The remaining classesof vertebrates (Reptilia,
Aves, Mammalia) are
collectively called
amniotes referring tothe way they
reproduce.
KK Fig. 5.29, H&G Fig. 5.11
They lay descication-resistant, amniotic eggs
on land, or bear live young. These eggs require internal
fertilization.
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Class Reptilia
Reptilia are the first truly terrestrial vertebrates. They arenot restricted to damp environments.
They have dry, keratinized skin that resists moisture loss
and allows them to bask and raise their body
temperatures.
They lay amniotic eggs on land or retain their eggs
internally to produce live young.
The first reptiles appear in the fossil record about 300
mybp.
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The various reptile taxa ending in apsida are named for
the openings or apses in the temple region of the skull.
H&G Fig. 8.18
KK Fig. 3.28
Reptile Skulls
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Subclass Mesosauria
250-300 mybp
Early reptiles, secondarily aquatic.
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Parareptilia
In 2008, a description of an early turtle from China was published that
illustrates how the turtle shell evolved. (Nature 456: 497-501)
KK 3.30
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Class ReptiliaEureptiliaIncludes:
Dinosaurs (ornithischians,
saurischians, pterodactyls,
thecodonts, icthyosaurs, plesiosaurs).
Crocodilians (alligators, crocodiles)
Snakes and lizards.
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Eureptilia dominated the fauna of the land for
>100 million years during the Jurassic and
Cretaceous periods.
They gave rise to the birds, and some believethat birds should be included in the Reptiles.
The two main dinosaur groups are named for
the structure of their hips.
Eureptilia, DinosaursKK 3.36, H&G 4.7
KK 3.35
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Aquatic EureptiliaThese are the ones that are sometimes referred to as euryapsids.
KK Fig. 3.22
H&G 4.8
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Flying Eureptilia Pterosaurs or pterodactyls
Some pterosaurs
were larger thanany modern bird,
up to 12 m in
wingspan.
KK
3.34
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Modern Eureptilia include crocodilians, Sphenodon,and lepidosaurs (snakes and lizards)
KK
3.34KK 3.33
H&G 4.5, 4.6
(Tuatara)
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Synapsida
Synapsida are often called mammal-like reptiles and are thought to be ancestral to the
mammals. Kardong does not consider them to be reptiles.
They appeared at the same time as Eureptilia, but went extinct as dinosaurs radiated in
the Jurassic.
mammalian characterstics: dentition, details of the skull, limb girdles, gait,
endothermy? hair? mammary glands?
KK 3.43,3.44
H&G 4.3
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