Key to Adult Turtles of Illinois

1a. Bony shell covered with leathery skin … 2

1b. Bony shell covered with large scutes (Fig. 13a) … 3

labelled illustration of False Map Turtle's carapace and plastron
Figure 13. Carapace (a) and plastron (b) of the False Map Turtle

2a. Anterior edge of carapace with small tubercles or spines; interior of nostrils with horizontal projections (Fig. 14a) … Spiny Softshell

2b. Anterior edge of carapace smooth; interior of nostrils lack projections (Fig. 14b) … Smooth Softshell

labelled drawing of nostrils of softshell turtles
Figure 14. Looking head-on into the nostrils of softshell turtles: (a) Spiny Softshell showing horizontal projections, (b) Smooth Softshell showing rounded nostrils

3a. Plastron with 11 or more plates contacting at midline (Fig. 13b); tail short (less than one-half shell length) … 4

3b. Plastron with fewer than 11 plates contacting at midline (Fig. 15); tail long (greater than one-half shell length) … 5

plastron of Snapping Turtle
Figure 15. Plastron of the Snapping Turtle showing 9 plastral plates. The horizontal elements are part of the bridge and not considered plastral plates.

4a. Carapace (usually) with 11 pairs of marginal scutes (Fig. 13a); plastron with fewer than 6 pairs of scutes (Fig. 13b) … 6

4b. Carapace (usually) with 12 pairs of marginal scutes (Fig. 13a); plastron with 6 pairs of scutes (Fig. 13b) … 8

5a. Carapace with a single row of marginal scutes and 3 low keels that disappear with age … Snapping Turtle

5b. Carapace with an extra row of scutes between marginals and pleural scutes 1-3 on each side (Fig. 16) and 3 prominent keels that do not disappear with age … Alligator Snapping Turtle

side view of Alligator Snapping Turtle's carapace
Figure 16. Side view of the carapace of the Alligator Snapping Turtle showing the extra row of scutes called supramarginals (S) between marginals and pleural scutes 1-3

6a. Skin showing between plastral scutes; pectoral scutes square (Fig. 17a); a single poorly developed plastral hinge anteriorly … Eastern Musk Turtle

6b. Skin not showing between plastral scutes; pectoral scutes triangular (Fig. 17b); 2 well-developed plastral hinges … 7

Figure 17. Plastrons: (a) Eastern Musk Turtle with skin between plastral scutes (stippled areas) and squarish pectoral scutes (P); (b) Yellow Mud Turtle without skin between plastral scutes and triangular pectoral scutes (P)

7a. Marginals 8 and 9 are of approximately equal height (Fig. 18a) … Eastern Mud Turtle

7b. Marginal 9 much higher than 8 (Fig. 18b) … Yellow Mud Turtle

side view of carapaces of Eastern Mud Turtle and Yellow Mud Turtle
Figure 18. Side view of the carapace: (a) Eastern Mud Turtle showing marginals 8 and 9 as approximately equal in height; (b) Yellow Mud Turtle showing marginal 9 much higher than marginal 8

8a. Plastron hinged between pectoral and abdominal scutes … 9

8b. Plastron not hinged … 11

9a. Chin and throat bright yellow; upper jaw notched … Blanding’s Turtle

9b. Chin and throat not bright yellow; upper jaw hooked … 10

10a. Carapace and plastron with radiating yellow lines; peak of carapace flattened and lacking a keel … Ornate Box Turtle

10b. Carapace pattern variable; plastron lacking discrete pattern of light lines; peak of carapace dome-like with median keel … Eastern Box Turtle

11a. Carapace black with prominent yellow spots … Spotted Turtle

11b. Carapace variable, without prominent yellow spots … 12

12a. Marginal scutes or plastron marked with red … Painted Turtle

12b. Marginal scutes and plastron not marked with red … 13

13a. Head pattern posterior to the eye comprised only of longitudinal stripes extending onto neck … 14

13b. Head pattern posterior to the eye includes a spot or horizontally oriented stripe or bar in addition to longitudinal stripes … 15

14a. Prominent red or orange stripe behind the eye; plastron with single dark spot or smudge per scute (head striping may be obscure in old, dark males but some plastral spots typically remain) … Pond Slider

14b. All head stripes yellow; plastron with little or no pattern … River Cooter

15a. Yellowish spot or comma-shaped marking behind the eye; median keel of carapace low and lacking prominent knobs … Northern Map Turtle

15b. Conspicuous blotch, crescent, or horizontally oriented stripe or bar behind the eye; median keel of carapace topped with low black knobs on vertebral scutes 2-4 … 16

16a. Broad, squarish to rectangular blotch or bar behind the eye; spot under the eye and spot on lower jaw with a diameter greater than the iris (Fig. 19a) … Ouachita Map Turtle

16b. Narrow stripe or crescent behind the eye; if present, spot under the eye and spot on lower jaw with a diameter less than the iris (Fig. 19b) … False Map Turtle

head patterns of false map turtles
Figure 19. Head patterns of false map turtles: (a) Ouachita Map Turtle, (b) False Map Turtle