All chordates have dorsal tubular nerve cords. All chordates are vertebrates. Chordates are found in all major types of environments. The term agnathan could be used to describe a. ostracoderms. Exchange of respiratory gases through the skin is a characteristic of many a. fish.
Amphibians are completely dependent on an aquatic environment for a. respiration.
Mammals are the only vertebrates that possess a. teeth. According to the Gaia hypothesis, the earth will eventually cool down to the point that the oceans will freeze. The evolutionary trend of bipedalism refers to the a. ability of only humans to ride a bicycle. Fossil evidence suggests the earliest members of the genus Homo were a. social. Carbon Dioxide d. ozone 40.