|Amphibian Species, Threatened (Number)|
The Amphibians are divided between three higher-level ranks or Orders: Gymnophiona, Anura and Caudata, with Anura and Caudata being more closely related to each other than either is to the Gymnophiona. Based on the results of the Global Amphibian Assessment (as of December 2006), the Anura is comprised of the frogs (and their subgroup, the toads), and is by far the largest Order, with 5.208 living species currently recognized. The Caudata (salamanders and newts) contains 535 described living species and is the second largest of the three amphibian Orders, although representing only about 10% of the number of species as frogs. The Gymnophiona (caecilians) is the smallest of the three amphibian Orders (with only 172 described species), even though the group is at least as old as all of the diversity of salamanders and frogs taken together. Because they tend to be rare animals in collections, the taxonomic status of many caecilian species is uncertain. Threatened species are the number of species classified by the IUCN as endangered, vulnerable, rare, indeterminate, out of danger, or insufficiently known.