Question

Structural similarities and differences among organisms can be studied to understand evolutionary relationships. This process is called comparative anatomy. The structures may be labeled as homologous or analogous. Homologous refers to structures in different organisms that have the same evolutionary origin. These structures may have different functions in different animals, but they share a common ancestor. Analogous refers to structures in organisms that serve the same purpose and function, but the organisms have different evolutionary ancestors. Although these structures may appear to be related, they have different origins. Scientists must consider how the organisms developed and evolved to determine if structures are homologous or analogous.



The diagram shows the fins of a shark and a dolphin, and the tails of an alligator and a turtle.



The sharks have supporting rods inside their first dorsal fin. The dolphins dorsal fin is dense, fibrous connective tissue with no bone, cartilage or muscle. The alligator's tail is large with wider vertebrae-style bones narrowing down to small bones. The turtle's tail is small with vertebrae-style bones.



Why do the tails of the alligator and the turtle look similar?


They both use them to swim in water.


They both reproduce by laying eggs.


They have a common ancestor.


They live in the same environment.

Answer 1

They have a common ancestor.

Explanation: The alligator and turtle tails have similar vertebrae-style bones, indicating a shared evolutionary origin (homology). Similar function or environment (swimming, egg-laying) does not explain the same internal bone structure.