Vertebrate Keys

1 a. Fins present
b. Fins absent
2
3
2 a. Jawless; several gill openings behind head
b. Bony jaws present; usually a single gill opening behind head covered by an operculum
Agnatha
Osteichthyes
3 a. Skin naked, with no protective coverings
b. Skin with scales or other protective coverings
Amphibia
4
4 a. Skin with scales; feathers or hair not present
b. Skin without scales; either feathers or hair present
Reptilia
5
5 a. At least some part of body with feathers
b. At least some part of body with hair
Aves
Mammalia