Amphibians and Reptiles
Main sources: Stebbins, Robert C., 1985, A Field Guide to Western Reptiles and Amphibians. The Peterson Field Guide Series. Boston: Houghton Mifflin Co.; Behler, John & Wayne King, 1979, The Audubon Society Field Guide to North American Reptiles and Amphibians, NY; Brennan, Thomas & Holycross, Andrew, 2006, Amphibians and Reptiles in Arizona. Phoenix: Arizona Game & Fish Department. See also the UC Berkeley Taxon Lift.
Amphibians and reptiles are tetrapods -- terrestrial vertebrates that bear four jointed limbs, possessing digits rather than fins. The oldest known Tetrapod forms date no later than the Mississipian period (350 MYA) of the Paleozoic Era, and were probably Amphibians. Tetrapods today include two broad groups -- the Amphibians (including frogs and toads, salamanders and newts, and caecilians) -- animals whose soft eggs must be laid in water and are fertilized by the male externally, and whose embryos first swim in water like fish before metamorphosing into tetrapods), and the Amniotes, carriers of the amnion, a layer within the egg or womb which replaces the aquatic enviroment required for developing embryos (and who are therefore freed from an imposed reproductive connection with external bodies of water). Reptiles are amniotes (and apparently the earliest reptiles were all egg-layers, though some now bear live young), and birds and mammals (including ourselves) are also amniotes. Birds in fact are now classified as a line of reptiles, being descended from a Dinosaur lineage, but for sake of familiar traditions we deal with them separately here. Living Amniotes differ from Amphibians in more ways than reproduction: their brains are significantly different -- amniotes possess a dynamic, flowing visual consciousness which appears to be absent in amphibians, whose visual world appears to be entirely automatic.
Amphibians became numerous by the late Paleozoic, and familiar forms of frogs, toads, and salamanders are in evidence by Jurassic times (216-145 MYA). The Amniotes have a complex history: they are now divided into the Anapsida (the turtles and their extinct kin, dating at least from the lower Permian, 280 MYA), Diapsida (the main group of reptiles, dinosaurs, and birds, ancestors probably dating from the Pennsylvanian, 300 MYA), and Synapsida (the mammals and their extinct relatives, also probably dating to the late Permian Period). See this link (from the UC Berkeley Taxon Lift) for more details on tetrapod evolution and ecology.
While recent evolutionary systematics shows amphibians and reptiles to be more remotely related than the latter are to birds, etc., herpetology (Greek: the study of creeping animals) emerged as a scientific field lumping amphibians and reptiles together on the basis of such features as locomotion, skin and "cold-bloodedness". Today it remains a vital discipline, and we follow this tradition in grouping the two classes of animals together here.
For excellent, detailed listings (and images) of reptiles and amphibians in our general area, click on this Tucson Herpetological Society website link.
For information and images from our specific area, click on the links below to open each page.