Question

Sharks, whales, and dolphins share similar features such as body shape and the position of fins. However, sharks have gills for breathing, while whales and dolphins have lungs. These differences indicate that the organisms share a common ancestor for:

_______ - Both body structure and breathing structures.

_______ - Evolved from organisms with legs.

Answer 1

The similar body shapes and fin placement of sharks, whales, and dolphins compared to fish are due to analogous traits, a result of convergent evolution owing to adapting to similar aquatic environments. Their breathing structures, however, diverge as sharks have gills and whales and dolphins have lungs, highlighting their evolutionary differences despite common physical characteristics.

Step-by-step explanation:

Sharks, whales, and dolphins showcase similarities in body shape and fin placement, yet they differ significantly in their breathing structures; sharks have gills, while whales and dolphins have lungs. This phenomenon can be explained through the principles of analogous and homologous traits. An analogous trait is one in which species share features due to similar environmental pressures, not shared ancestry. For example, the similar body shapes of dolphins and fish are a result of convergent evolution, where unrelated species independently evolve similar traits as a consequence of adapting to comparable environments or ecological niches. Contrastingly, a homologous trait is one where species share features due to a common ancestor, such as the limb bones in humans, dogs, birds, and whales, which indicate a shared lineage.

Mammals such as whales, dolphins, and porpoises have a unique evolutionary history, as they returned to the ocean after their ancestors had lived on land. Therefore, their similarities to fish are analogous, because they result from adapting to life in aquatic habitats, even though fish and mammals took different evolutionary paths post their divergence about 400 million years ago.

The body structure of whales and dolphins found in the ocean today is adapted from land-dwelling ancestors, indicating that the similar construction of their appendages is due to a common ancestor, which is a homologous trait. However, their adaptations for aquatic life, which are similar to those of fish, such as their streamlined body shape and fin placement, are analogous traits, derived independently as both groups adapted to similar environmental pressures.