Answer the following question given this paragraph: 

Birds are endothermic tetrapod vertebrates. They are bipedal, which means they walk on two legs. Birds also lay amniotic eggs, and the eggs have hard, calcium carbonate shells. Although birds are the most recent class of vertebrates to evolve, they are now the most numerous vertebrates on Earth. Why have birds been so successful? What traits allowed them to increase and diversify so rapidly?.


Q: What type of vertebrates are birds?

 Choices:

- epidermal tetrapod

- invertebrates

- exothermic

- endothermic tetrapod

A:
endothermic tetrapod
