Reptiles are characterized by having dry skin with keratinized epidermal scales. In addition to their scales, reptiles have true claws (if limbs are present). If they lay eggs (some give live birth), the eggs are amniotic and have a shell that allows them to develop in a manner less reliant on water than amphibians. The class Reptilia includes the orders: Testudines (tortoises and turtles), Crocodylia (alligators and crocodiles), Rhynchocephalia (Tuatara), and Squamata. Squamata includes the suborders Sauria (lizards) and Serpentes (snakes). The orders represented here in Idaho are Testudines and Squamata
The reptiles that comprise the order Testudines are easily recognizable. No other vertebrate has the hard shell that surrounds and protects the organs of turtles. Turtle shells consist of two basic parts, the top shell which is referred to as a carapace, and a bottom shell that is known as a plastron. The two parts of the shell are connected on each side by a portion of the shell known as the bridge. Turtle ribs and vertebrae, with the exception of the neck and tail, are fused to form the carapace (Pough et al., 1998). The outer surface of turtle shells are comprised of keratinized scutes or laminae (Goin and Goin, 1971). The Latin word-root "test" is synonymous for shell, and the order name "Testudines" is Latin for turtle.
Turtles are oviparous and have internal fertilization. Fertilization is accomplished by a penis which is an outgrowth of the cloacal wall (Pough et al., 1998). Turtle eggs are buried in a nest and left to incubate and hatch. Another feature of Testudines is the lack of teeth. The jaws of many Testudines are sharp-edged or serrated to provide a cutting surface. The beak is covered by a horny layer of keratin.
A final characteristic we will mention here is the lack of holes in the temporal region of the skull, a condition known as anapsis. This feature is unique among living reptiles (Goin and Goin, 1971; Pough et al., 1998).
Not only are turtles easy to identify as being members of the order Testudines, in Idaho there is only a single representative. The Painted Turtle (Chrysemys picta) is in the family Emydidae, which is one of twelve families that comprise the order Testudines.
Characteristics of the order Squamata include a transverse vent or cloacal opening (Goin and Goin 1971), skulls that are more moveable (or kinetic) than other reptile orders, paired copulatory organs called hemipenes, keratinous scales that cover the body, and the shedding of the outer epidermal layer (ecdysis). Other evolutionary trends for many Squamates include the loss or reduction of limbs and the ability to lose the tail (caudal autotomy) at distinct fracture planes (Pough et al. 1998)
The order Squamata is the most diverse of the reptile orders, containing 96% of the reptile species (Nussbaum et al. 1983). In Idaho, there are 21 species of squamates, but only 1 species of testudines and no species of crocodylians. Within the Idaho squamates, there are enough distinct differences to address the lizards (Lacertilia) and the snakes (Serpentes) separately.
Characteristics that distinguish Idaho Lacertilia from the group Serpentes are the presence of four limbs (there are some lizards species elsewhere that lack limbs), visible ear openings, and movable eyelids. These three characters alone should allow you to readily recognize Idaho lizards.
Snakes have several unique characteristics that should allow you to readily identify them as members of the group Serpentes. All snakes lack limbs; there are however, some species that have vestigial limbs in the form of small spurs (e.g. the rubber boa). All snakes lack eyelids; there are some lizard species that lack eyelids, but none in Idaho. Snakes have no external ear opening; some burrowing lizards lack ear openings as well, but all Idaho lizard species have an external ear opening. Finally, snakes have a elongate body. Again, there are some lizard species that are limbless and have long slender bodies, but none of these species occur in Idaho.