Origin of Amphibians
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What geological time period to the earilest amphibian fossils appear?
Late Devonian period
Name the two fish subclasses
- Actinopterygii (ray-finned fishes)
- Sarcopterygii (lobbed-finned fishes)
~Most of the fish we know of today
~ Lack internal nares
Actinopterygii (lobbed-finned fishes)
~Gave rise to amphibians and all tetrapods
~Have internal nares
Name the two orders of Sarcopterygii
- Dipnoi (lungfish)
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
Name the two suborders of Crossopterygii
- Marine forms
- Most members are extinct (one that was thought to be extinct was found in the Indian ocean-deep waters)
- Freshwater forms
- All are extinct
- Gave rise to amphibians and all tetrapods
Name the three subclasses of Amphibia
- Labyrinthodontia (all extinct)
- Lepospondyli (all extinct)
- Lissamphibia (the modern orders)
Name the three orders of Labyrinthodontia
Which Labyrinthodontia order gave rise to reptiles? What geological time period did they go extinct?
- They went extinct by the end of the Permian
What geological time period did reptile show up?
The oldest fossils found in the Devonian were from?
What geological time period do the modern amphibian start to show up?
What type of teeth do all amphibians have?
Which is the only fish to have Labyrinthodont teeth?
- 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
What major anatomic characteristic links amphibians back to Crossopterygii?
- Existed from Mississippian through Periman (about 100 million years)
- Gave rise to reptiles during the Mid-Permian (250 mya)
- 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
The enamel forms infoldings or Labyrinths
- Probably entirely aquatic
- Bizarre body shapes, but most are small and bring to mind salamander body shape (strange heads)
- Extinct by early Permian
- 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
- 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)
- 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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