A class of amphibians, the order Anurans contains all of the world's frogs and toads. These creatures are defined by their large eyes, moist skin, relatively large hind legs, and lack of a tail. Amphibians split from their closest primitive relatives, the lobe-finned fish, in the Devonian as the first tetrapods to set foot on land1. Examining the morphology of these animals can elucidate much of what makes amphibians such excellent candidates for land colonization. They had fingers that allowed them to walk (albeit clumsily) on land, lungs that allowed them to breathe the air above them, and the beginnings of a neck that would allow them to attack moving prey. . Over time, the clade diversified and Vieraella herbstii, the first known “true frog” without a tail, appeared in the late Jurassic2. The appearance of V. herbstii marked the beginning of the Anura order. Like all amphibians, Anurans do not have the ability to produce amniotic eggs. Because they are unable to lay eggs on land, almost all organisms in this class spend their lives near a freshwater source. Frogs need fresh water to lay eggs and pass on their genes, but without a source of fresh water nearby, any lineage of frogs will dry out. Another limitation faced by all amphibians, not excluding frogs, is the fact that their skin is vital for their respiration. They absorb O2 and release Co2 through their porous envelope and to do this, they must remain humid3. Desiccation is a very real threat to all amphibians, which is why they are largely found in tropical environments and other areas with high humidity and precipitation. Frogs are all carnivores that feed primarily on arthropods like insects and spiders, but some of the larger breeds can prey on them. on small mammals and birds. Their s...... middle of paper ......//sci.waikato.ac.nz. University of Waikato, nd Web. March 31, 2014. .[2] Evans, SUSAN E., ANDREW R. Milner, and FRANCES Mussett. “A discoglossid frog from the Middle Jurassic of England.” Paleontology 33.2 (1990): 299-311.[3] Reece, Jane B. and Neil A. Campbell. Campbell Biology / Jane B. Reece... Boston: Benjamin Cummings, 2011. Print.[4] Levine, RP "Contribution of eye retraction to swallowing performance in the northern leopard frog, Rana Pipiens." Journal of Experimental Biology207.8 (2004): 1361-368. Print.[5] Fryer, Benjamin. “Rana Pipiens.” AmphibiaWeb.com. Amphibiaweb, June 4, 2004. the web. April 3, 2014.[6]Gilbert SF. Developmental biology. 6th edition. Sunderland (MA): Sinauer Associates; 2000. The life cycle of the frog. Available at: http://www.ncbi.nlm.nih.gov/books/NBK10035/