Question

What derived characters do sharks and tuna share? What features distinguish tuna from sharks?

Short answer

Both sharks and tuna are gnathostomes and have jaws. They also have enlarged forebrains. The skeleton of a shark is made of cartilage, whereas tunas have a bony skeleton.

Step-by-step solution

Classification of sharks and tuna

Sharks are vertebrates that belong to the clade Chondrichthyes (cartilage fish). On the other hand, tuna belong to the clade osteichthyans, Actinopterygii. They both evolved from a common ancestor around 400 million years ago and are a classic example of convergent evolution.

Similarities between shark and tuna

Sharks and tuna are both gnathostomes with a body shape that allows them to swim efficiently; they both have a lateral line system for predator detection (vibrations). They also have bigger brains, jaws, and four clusters of Hox genes.

Difference between shark and tuna

The skeletons of sharks are made of cartilage. They have a spiral valve that increases the intestine’s surface area. On the other hand, tunas have a bony skeleton. They have a swim bladder and an operculum.

They also have flexible rays that support their fins for swimming. Thus, they are called ray-finned fishes.