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Fossils of lobe-finned fishes, which are ancestors of amphibians, are found in rocks that are at least 380 million years old. Fossils of the oldest amphibian-like vertebrate animals with true legs and lungs are found in rocks that are approximately 363 million years old. Three samples of rocks are available that might contain fossils of a transitional species between lobe-finned fishes and amphibians: one rock sample that is 350 million years old, one that is 370 million years old, and one that is 390 million years old. (a) Select the most appropriate sample of rocks in which to search for a transitional species between lobe-finned fishes and amphibians. Justify your selection. (b) Describe TWO pieces of evidence provided by fossils of a transitional species that would support a hypothesis that amphibians evolved from lobe-finned fishes.

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Answer:

(a) The most appropriate sample of rocks in which to search for a transitional species between lobe-finned fishes and amphibians is the one that is 370 million years old.  

(b)  Extremities´ bones and inner ear.

Explanation:  

(a) Lobe-finned fishes are ancestors of amphibians, and their fossils are found in rocks that are at least 380 million years old. On the other hand, the oldest amphibian-like vertebrate animals with true legs and lungs are found in rocks that are approximately 363 million years old. According to this information:

  • The rock sample that is 350 million years old, contains the fossil of a species that is intermediate between the actual forms and the oldest amphibian-form.
  • The rocks that are 390 million years old, contains the fossil of a species that is even older than the Lobe-finned fishes
  • Only the rock that is 370 million years old contains the transitional species between lobe-finned fishes and amphibians.

(b)

  • Extremities´ bones: Fishes had to adapt to a new locomotor strategy, such as walking on land. Their pectoral and pelvic fins suffered changes and evolved, becoming very similar to the amphibian's extremities. The bones of the Lobe-finned fishes' extremities are homologous with the bones of the amphibians´extremities.
  • Inner ear: Fishes also had to adapt to hearing in a completely new environment, so they suffered changes in their inner ear.      

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