The Linnaean Classification System

How did Linnaeus group species into larger taxa?

In addition to creating the system of binomial nomenclature, Linnaeus also developed a classification system that organized species into taxa that formed a hierarchy or set of ordered ranks. Linnaeus's original system had just four levels. Over time, Linnaeus's original classification system expanded to include seven hierarchical taxa: species, genus, family, order, class, phylum, and kingdom.

We've already discussed the two smallest categories, species and genus. Now let's work our way up to the rank of kingdom by examining how camels are classified. The scientific name of a camel with two humps is Camelus bactrianus. (Bactria was an ancient country in Asia.) As you can see in Figure 18–5, the genus Camelus also includes another species, Camelus dromedarius, the dromedary, which has only one hump. In deciding how to place organisms into these larger taxa, Linnaeus grouped species according to anatomical similarities and differences.

FIGURE 18–4 Carolus Linnaeus

▸ Family The South American llama bears some resemblance to Bactrian camels and dromedaries. But the llama is more similar to other South American species than it is to European and Asian camels. Therefore, llamas are placed in a different genus, Lama; their species name is Lama glama. Several genera that share many similarities, like Camelus and Lama, are grouped into a larger category, the family—in this case, Camelidae.

▸ Order Closely related families are grouped into the next larger rank—an order. Camels and llamas (family Camelidae) are grouped with several other animal families, including deer (family Cervidae) and cattle (family Bovidae), into the order Artiodactyla, hoofed animals with an even number of toes.