Many species (for example, Cook's robber frog, E. cooki), also of Puerto Rico, exhibit sexual dimorphism in size and color.

Study on Eleutherodactylus and Lithobates amphibians shows that number of offsprings instead of body size may help to find which species require conservation from being extinct.

[8] The oldest fossil of Eleutherodactylus is a partial humerus from the Early Oligocene-aged San Sebastián Limestone of Puerto Rico, likely not long after the genus first dispersed to the Caribbean from South America.

All true members of the genus have been clustered into subgenera, but many less-related species require more genetic data before they are to be officially classified elsewhere.

The fossil record, combined with molecular clock analyses, indicate the subgenera were probably founded by small groups of individuals by flotsam dispersal from South America during the Eocene or Oligocene epochs.

Land bridges would have been limited to facilitating dispersal between West Indian islands, however, the Oligocene division of Hispaniola and Cuba resulted in further speciation.

The formation of the Panama Isthmus during the Pliocene has caused some intercontinental distribution among the clades, although only 20 "South American frogs" have ever made it northwards after the original colonization.