Presence of gills in the tadpole of frog indicates that frogs evolved from gilled ancestors.

Explanation:

Gills are respiratory organs that allow aquatic organisms to extract oxygen from water. The presence of gills in the tadpole stage of a frog suggests that frogs have evolved from ancestors that had gills. This is because gills are typically found in aquatic organisms, and frogs undergo a metamorphosis from a water-dwelling tadpole to a land-dwelling adult.

Key Points:

1. Gills in tadpoles: Tadpoles are the larval stage of frogs and are fully aquatic. They possess external gills, which are used to extract oxygen from water.
2. Metamorphosis: During metamorphosis, tadpoles undergo significant physiological and anatomical changes to transform into adult frogs. This includes the development of lungs for breathing air instead of relying on gills.
3. Adaptation to terrestrial life: Adult frogs have adapted to life on land and have lungs as their primary respiratory organ. They breathe air directly through their lungs, whereas tadpoles rely on gills to extract oxygen from water.
4. Evolutionary perspective: The presence of gills in the tadpole stage suggests that frogs have evolved from ancestors that were adapted to an aquatic lifestyle. These ancestors would have possessed gills as their primary respiratory organs.
5. Evolution of lungs: Through evolutionary processes, frogs have developed lungs to breathe air and have become highly adapted to life on land. This transition from an aquatic to a terrestrial lifestyle is a significant evolutionary change.
6. Evidence from other amphibians: Other amphibians, such as salamanders and newts, also have aquatic larval stages with gills. This further supports the idea that frogs evolved from gilled ancestors.

In conclusion, the presence of gills in the tadpole of a frog indicates that frogs evolved from ancestors that had gills as their primary respiratory organs. This adaptation allowed them to transition from an aquatic to a terrestrial lifestyle through the process of metamorphosis.