Question

how can we say that birds are closely related to reptiles and have evolved from them

Answer 1

as reptiles like dinosaurs first came into the existence they had feathers but due to their heavy body they were not able to fly so when birds cane into the existence they were able to fly as we can say the modification.

Answer 2

Birds are related to reptiles. This statement can be justified by the given explaination :

Dinosaurs belongs to the class named reptiles. Dinosaurs had feathers on their body. These feathers helped them to be warm in the cold conditions and weather.

Later on, in the process of evolution, feathers appeared on birds. These helped the birds to fly in the sky.

Also, they both share same features like : laying eggs, having sacles on their feet, etc.

Such similarity justifies that birds have evolved from reptiles.