Which of the Following Could Be Considered the Most Recent

Question

Which of the following could be considered the most recent common ancestor of living tetrapods?
A)a sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebrates
B)an armored, jawed placoderm with two pairs of appendages
C)an early ray-finned fish that developed bony skeletal supports in its paired fins
D)a salamander that had legs supported by a bony skeleton but moved with the side-to-side bending typical of fishes

Accepted Answer

The sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebrates is considered the most recent common ancestor of living tetrapods. This is because tetrapods are believed to have evolved from lobe-finned fishes, and this ancestor had features that were transitional between fishes and tetrapods, such as the presence of skeletal supports in its fins that could have helped it move on land. Placoderms and ray-finned fishes are not ancestors of tetrapods, and the salamander described in choice D has already evolved into a tetrapod and is not an ancestor of living tetrapods.