12. How do relatively complete fossil records, such
as the horse fossil record, provide evidence for
evolution and common ancestry of organisms?

They show us exactly when and how the organism has changed and evolved through time.

Explanation:

The horse fossil record shows us how the legs of earliest horse ancestors ended in padded feet with four functional hooves on each of the forefeet and three on each of the hind feet—quite unlike the unpadded, single-hoofed foot of modern horsed. The fossil record from there on shows uh how the transition continued.

where is the scientific experiment?

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.