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What geological time period to the earilest amphibian fossils appear?
Late Devonian period
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Name the two fish subclasses
- Actinopterygii (ray-finned fishes)
- Sarcopterygii (lobbed-finned fishes)
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~Most of the fish we know of today
~ Lack internal nares
Actinopterygii (lobbed-finned fishes)
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~Gave rise to amphibians and all tetrapods
~Have internal nares
Sarcopterygii
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Name the two orders of Sarcopterygii
- Dipnoi (lungfish)
- Crossopterygii
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What demonstates that amphibians arose from Crossopterygii rather than lungfish? Why?
- Fin anatomy
- Here's why: Lungfish limbs are not built well for moving long distances on land
- Crossopterygians have larger bones in their limbs which are posed for terrestrial evolution
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Name the two suborders of Crossopterygii
- Coelacanthiformes
- Rhipidistia
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Coelacanthiformes
- Marine forms
- Most members are extinct (one that was thought to be extinct was found in the Indian ocean-deep waters)
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Rhipidistia
- Freshwater forms
- All are extinct
- Gave rise to amphibians and all tetrapods
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Name the three subclasses of Amphibia
- Labyrinthodontia (all extinct)
- Lepospondyli (all extinct)
- Lissamphibia (the modern orders)
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Name the three orders of Labyrinthodontia
- Icthyostegalia
- Anthracosauria
- Temnospondyli
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Which Labyrinthodontia order gave rise to reptiles? What geological time period did they go extinct?
- Anthracosauria
- They went extinct by the end of the Permian
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What geological time period did reptile show up?
Mid-Permian
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The oldest fossils found in the Devonian were from?
Icthyostegalia
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What geological time period do the modern amphibian start to show up?
Jurassic
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What type of teeth do all amphibians have?
Labyrinthodont teeth
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Which is the only fish to have Labyrinthodont teeth?
Crossopterygii
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Icthyostegalia
- Oldest fossils (Devonian)
- Have a fish-like skull, but pectoral girdle no longer articluates with the skull
- Limbs are well developed
- Have neural spines (processes) for muscle attachment
- Pelvic girdle articulates with sacrum
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What major anatomic characteristic links amphibians back to Crossopterygii?
Labyrinthodont teeth
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Anthracosauria
- Existed from Mississippian through Periman (about 100 million years)
- Gave rise to reptiles during the Mid-Permian (250 mya)
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Temnospondyli
- A very successful group.... Existed from Mississippian through Triassic (all extinct)
- Began mostly as freshwater aquatic forms
- Some became terrestrial
- Others became marine
- Most modern Herpetologist believe that Lissamphibia (modern amphibians) arose from Temnospondyli
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Labyrinthodont teeth
The enamel forms infoldings or Labyrinths
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Lepospondyli
- Probably entirely aquatic
- Bizarre body shapes, but most are small and bring to mind salamander body shape (strange heads)
- Extinct by early Permian
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Lissamphibia
- Three modern orders and one extinct order (Anuran, Apoda, Caudata, and Proanuran)
- Huge gaps in fossil records make it difficult to determine where these came from
- Has adaptations (extinct one don't)
- Pedicellate teeth
- Green rods in eyes
- Fat bodies from gonadal ridge
- Unique skin glands
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Pedicellate teeth
- Grow as two parts: Pedicel (base part) and crown
- Pedicel is located under the gum line
- Crown is sticks out through the gum
- As crown wears out, pedicels replace them (throughout life)
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Conflicting theories
- Some believe that anurans and caecilians evolved from Temnospondyli and that salamanders evolved from Lepospondyli
- Since all modern orders have the unique characteristics, it is unlikey these all evolved indentdently in all three groups
- Most herpetologists believe that Lissamphibia arose from Temnospondyli
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