4 - Tetrapods I

7/27/2019 4 - Tetrapods I

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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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4 - Tetrapods I