Ineed on this question, i dont know what to fill it

So basically its like every animal has all the leading characteristics. for example, you marked that the shark has a vertebra that is correct now you would go onto the Ray-finned fish, you would follow the cladogram lines and x off Vertebra and Bony skeleton you had this correct as well. Now going onto the Amphibians, you would follow the lines again as before and x off everything you've already ticked off plus four limbs because it falls underneath. you would do this for every category and characteristic. Hopefully, this makes sense!! The rest after Amphibians needs to be revised its not correct. :)

The answer would be abrasion.