Key to the Orders of U.S. Reptiles

Order names linked to a key for that order.

1 a. Animal with a bony or leathery shell
b. Animal without a bony or leathery shell		 Order Chelonia
2
2 a. Cloacal opening a longitudinal slit
b. Cloacal opening a transverse slit		 Order Crocodilia
3
3 a. 2 pairs of legs usually present; eyelids and external ear openings usually present
b. Legs absent; no eyelids or external ear openings
Order Squamata
Suborder Lacertilia
Suborder Ophidia

Key to the Families of Chelonia (Turtles)

Family names linked to common name examples.

1 a. Claws 3-3; carapace covered with skin; edge of carapace flexible
b. Claws 5-4 or 5-3; carapace covered with horny shields, or if no horny shields are evident, carapace skin with many projections giving it a roughened appearance		 Trionychidae
2
2 a. Plastron with 12 shields; pectoral shield forming front part of bridge
b. Plastron with 11 or fewer shields; pectoral shield not forming a part of bridge		 3
4
3 a. Top of head covered anteriorly with shields; digits short, without rudiment of web
b. Top of head covered anteriorly with undivided skin; digits usually elongate, nearly always with some web between toes		 Testudinidae
Emydidae
4 a. Tail generally long with a crest of large horny tubercles; rear of carapace strongly serrate
b. Tail generally short with fleshy papillae; rear of carapace nearly smooth		 Chelydridae
Kinosternidae

Family name with a common name example:

Key to the Families of Crocodilia

Family names linked to common name examples.

1 a. Snout broad; a tooth not visible when mouth is closed
b. Snout pointed; a tooth exposed when mouth is closed		 Alligator
Crocodylus

Family name with a common name example:

Key to the Families of Lacertilia (Lizards)

Family names linked to common name examples.

1 a. 2 pair of legs
b. Legs absent, or only forelegs present		 2
9
2 a. Eyelids present; pupils not vertical
b. Eyelids absent; pupils vertical		 3
8
3 a. All scales around body about equal in size; scales smooth, shiny
b. All scales around body not about equal in size; scales not smooth, shiny		 Scincidae
4
4 a. A skin fold extending from the head to the rear leg; scales of fold much smaller than those above and below it
b. No skin fold extending from head to rear leg; no lateral rows of scales smaller than dorsal or ventral scales		 Anguidae
5
5 a. Head covered with very small scales of about equal size
b. Head covered with scales unequal in size		 6
7
6 a. Ventral scales arranged in transverse rows
b. Ventral scales not in transverse rows		 Helodermatidae
Gekkonidae
7 a. Belly scales smaller than or equal to back scales
b. Belly scales larger than back scales		 Iguanidae
Teidae
8 a. Ventral plates rectangular; head plates large, 1 or 2 between eyes
b. Ventral plates rounded; head plates small, more than 10 between eyes		 Xantusidae
Gekkonidae
9 a. Only forelegs present, and these very small
b. No legs present		 Amphisbaenidae
10
10 a. Ear openings present
b. Ear openings absent		 Anguidae
Anniellidae

Family name with a common name example:

Vertebrate Key