Question

Ribs were first developed in

1) Arthropods

2) Reptiles

3) Aves

4) Echinoderms​

Answer 1

Answer:

in vertebrates ribs are firstly developed

I. e. in "reptiles" they are incompletely evolved but in mammals ribs are fully evolved, hence the ribs first time occurs in vertebrates and it evolves as class in vertebrates evolves.

3.3 million years ago

The skeleton of an early human ancestor found in Africa shows that some features were already established at least 3.3 million years ago, earlier than previously thought. The fossil was found to have only 12 rib-bearing vertebrae, the same number as modern humans — and one fewer than most apes.