Grouping animals by what they share
Animals are sorted into broad groups using features you can see and test
Animals are grouped by features you can observe — covering, breathing, habitat, food, reproduction.
Vertebrate = has a backbone · invertebrate = no backbone.
Mammals: hair or fur, feed young with milk. Birds: feathers and a beak. Insects: three body parts, six legs.
Breathe with lungs (mammals, birds, reptiles), gills (fish), lungs and moist skin (adult amphibians), spiracles (insects).
Warm-blooded (mammals, birds) keep a constant body temperature; cold-blooded animals do not.