Frogs: The Animal Answer Guide

2. Form and Function

13 13 What are the largest and smallest living frogs? A single species, the goliath frog (Conraua goliath), holds the undisputed record as the largest frog in the world. A native of Cameroon and Equatorial Guinea, the goliath frog inhabits West African rivers, especially near rapids and waterfalls. According to Victor Hutchison, who conducted research on the species, the largest goliath frog ever found was almost 16 inches long (not including the outstretched legs) and weighed more than 6½ pounds. Even the average size of these gigantic frogs in museum collections (7 to 11.8 inches and more than 2 pounds) is greater than the maximum size of nearly all other frogs in the world. Unfortunately, because of their large size, goliath frogs are a favored food item in some areas, which threatens their survival. Because of these and other threats to this impressive species, it is classified as endangered by the IUCN (International Union for Conservation of Nature). Frogs from other regions can also reach impressive sizes. The biggest frog in the United States and Canada is the bullfrog (Rana catesbeiana). The largest individuals reach 8 inches and more than a foot long with legs extended . Their famously huge hind legs have led to their popularity for edible frog legs, but their widespread distribution and abundance have kept them from being endangered in their native range. Two other members of the family Ranidae (the pig frog, Rana grylio, and the river frog, Rana heckscheri ) of North America also have strong back legs and reach large body sizes, although their maximum body length is less than 7 inches. The body length of the Colorado River toad (Bufo alvarius), which is found in the U.S. Southwest (mostly in Arizona) and ranges into Sinaloa Chapter 2 Form and Function 14 Frogs: The Animal Answer Guide in Mexico, rivals the bullfrog in body length. The largest individuals reach 7½ inches long. But their hind legs are relatively shorter than bullfrogs’ hind legs, and their total lengths with legs outstretched are less. Nonetheless , because of their massive body bulk, the Colorado River toad may grow heavier than any other native U.S. frog. In tropical America, several species are notable for their large sizes. The marine toad (Bufo marinus), also known as the cane toad, is arguably the largest toad in the world. Large adult females average 5 to 6 inches in body length, and the maximum size is reportedly more than 15 inches according to some records, with a weight of more than 5 pounds. Two other species, the rococo toad (Bufo schneideri) and the yellow cururu toad (Bufo ictericus), reach similar or possibly even larger sizes than the marine toad. The South and Central American bullfrog , or smoky jungle frog (Leptodactylus pentadactylus), reaches body lengths of more than 7 inches. Although no one debates that the goliath frog is the largest species in both length and weight, deciding which species is the smallest frog is not so easy. Many tiny contestants can be considered, and the true award for The goliath frog (Conraua goliath) of West Africa is the largest frog in the world. Courtesy Vic Hutchison 15 Form and Function smallness should go to the species in which the largest individual is smaller than the largest individual of all other species. Determining this is difficult , because who knows when someone might find a slightly bigger individual of the largest known specimen of a rare species at some point in the future. And in a practical sense it does not really matter. With a bit of geographic qualification, certain species would certainly be in the running as the “smallest frog.” Most amphibian biologists agree that the frog group with the greatest number of small species is the genus Eleutherodactylus in the family Leptodactylidae (or Eleutherodactylidae). But at least three other families (Brachycephalidae, Microhylidae, and Sooglossidae) have tiny representatives as well. Each of these families has a species whose typical adult size is around 1 cm, which is less than 0.4 inches. Two such frogs can sit together on an average person’s thumbnail without touching each other. But which actual species wins the designation for world’s smallest is difficult to determine. Included among the world’s midget frogs is Eleutherodactylus iberia of Cuba, a dark brown frog with a yellow stripe down each side and with no common name. Equally minuscule is Brachycephalus...