Humans, cats, whales, and bats belong to the phylum chordate. Based on the structure of their forelimbs, what can you infer about chordates?

They have a common ancestor (forelimbs are homolog structures in these species)

Explanation:

Homologous organs/structures refer to structures/organs which are similar in different species due they have been inherited from a common ancestor. The forelimbs of vertebrates (e.g., birds, humans, crocodiles, whales, bats, etc) are homologous structures derived from the same ancestral structure. In consequence, small variations related to the structure of the forelimbs in mammals such as humans, cats, whales, and bats represent adaptive functional modifications to their common early ancestors. On the other hand, analogous structures/organs are those that are similar and have the same function but evolved independently in two living organisms (e.g., the wings of birds and of bees).