Origin of Amphibians
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Origin of Amphibians
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
What demonstates that amphibians arose from Crossopterygii rather than lungfish? 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
Most members are extinct (one that was thought to be extinct was found in the Indian ocean-deep waters)
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)
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