Family (biology)
Class was the most general rank in the taxonomic hierarchy until phyla were introduced. Kingdom Animalia includes 108 classes including class Mammalia, Reptilia, Aves, etc. However, the classes used today are different from those proposed by Linnaeus and are not used frequently. For example, when it was discovered that birds are descendants of earlier dinosaurs, that caused some difficulties. In fact they are now so different from the original dinosaurs that it makes sense to teach and refer to them separately from dinosaurs.