What is the sign of the first terrestrial vertebrates indicating their origin from the ancient bristles?

this is the structure of paired limbs
The first terrestrial ones were probably ichthyostegs, descended from ancient beetle fish and giving rise to amphibians. The ancestors of amphibians could only be such fish that are able to breathe atmospheric air and crawl along the bottom, relying on paired fins.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.