Kinosternon flavescens

(Agassiz, 1857)
Yellow mud turtle

Yellow to brown in color, Kinosternon flavescens is a moderate-sized (to 16.5 cm) mud turtle with a broad, smooth, unserrated, medially depressed carapace lacking a medial keel. Its 1st vertebral scute is elongated, expanding anteriorly to touch the 2nd marginals. Vertebrals 2-5 are usually broader than long, and the 5th is somewhat expanded. Both marginals 9 and 10 are elevated. Dark pigment occurs along the seams. The plastron is large with two well-developed hinges; it is yellowish to brown, with dark pigment along the seams. The forelobe is as long as or slightly longer than the hindlobe; there is a shallow posterior notch. The gular is much shorter than half the forelobe length. The plastral formula is: an > abd > hum > gul >< fem > pect. Seldom do the axillary and inguinal scutes touch on the bridge. The head is moderate in size with a slightly protruding snout and a hooked upper jaw in males (only weakly hooked at best in females). Its rostral scale is strongly furcate posteriorly. The head is yellow to grayish; the jaws are whitish to yellow and may bear small dark spots. There are two pairs of barbels. Other skin is yellow to gray, and the tail is spine tipped.
The diploid chromosome number is 56: 26 macrochromosomes, 30 microchromosomes (Killebrew, 1975b). Stock (1972) reported 16 metacentric and submetacentric chromosomes, 8 subtelocentric, and 32 acrocentric and telocentric.
Males have long, thick tails and vinculae.

The yellow mud turtle occurs in northwestern Illinois and adjacent Iowa and Missouri, and from Nebraska south through Texas, New Mexico, and southern Arizona to Sonora, Durango, Tamaulipas, and Veracruz, Mexico. It has been found at elevations as great as 6500 m.

Geographic Variation
Three subspecies are recognized. The yellow mud turtle Kinosternon flavescens flavescens (Agassiz, 1857) ranges from southern Nebraska southward to Texas, New Mexico, and southeastern Arizona, and to immediately south of the Rio Pánuco basin in Veracruz, Mexico. It has a short gular scute (to 59% of forelobe length); a long interhumeral seam (8-25% of carapace length); a wide plastral hindlobe (36-49% of carapace length in males, 38-53% in females); and a short bridge (16-25% of carapace length). The Arizona mud turtle, K. f. arizonense Gilmore, 1922, is found in southern Arizona and Sonora, Mexico. It has a long gular (54-70%); a short interhumeral seam (8-15%); a narrow plastral hindlobe (35-42%); and a long bridge (21-28%). This subspecies was formerly known by the name williamsi, but Iverson (1979a) has shown it identical to fossils of arizonense described by Gilmore. The Durango mud turtle K. f. durangoense Iverson, 1979a is known from the Mexican states of Chihuahua, Coahuila, and Durango. It has a much shorter plastral forelobe (31-33% of carapace length; usually over 33% in the other subspecies); a long gular (54-69%); a short interhumeral seam (6-12%); a narrow plastral hindlobe (39-40% in males, 42-47% in females); and a long bridge (20-24%). The characters used are basically those of Iverson (1979a).
The populations in Illinois and adjacent Iowa and Missouri were formerly designated a separate race (K. f. spooneri Smith, 1951), but studies by Houseal et al. (1982) and Berry and Berry (1984) synonymized it with K. f. flavescens (although quite a controversy raged over its status; Dodd, 1982, 1983; Bickham et al., 1984; Gallaway et al., 1985). Collins (1991) suggested that K. f. arizonense be elevated to specific rank, as there is no demonstrable gene flow between it and K. f. flavescens.

Kinosternon flavescens inhabits almost any quiet water within its range: swamps, sloughs, sinkholes, rivers, creeks, ponds, lakes, reservoirs, cisterns, and cattle tanks in semiarid grasslands or open woodlands. A mud or sand bottom is preferred, and aquatic vegetation is often present.

Natural History
Male yellow mud turtles become sexually mature at carapace lengths of 8-9 cm in years 5-6; females mature at about 8-12.5 cm in 4-16 years (Mahmoud, 1967; Christiansen and Dunham, 1972; Long, 1986; Iverson, 1989b, 1991a). The annual male and female reproductive cycles are essentially like those reported under Sternotherus odoratus (Mahmoud and Klicka, 1972; Christiansen and Dunham, 1972; Christiansen et al., 1984; Long, 1986).
The courtship pattern is identical to that of Sternotherus odoratus (which see for details). K. flavescens may stay in coitus for 10 min to 3 h. Courtship usually takes place in water varying in depth from one inch to several feet, but a mating pair has been seen on land (Mahmoud, 1967).
Nesting occurs from May to August but is usually completed by 1 July. Clutches vary from one to six eggs, with two to four being most common; apparently only one clutch is laid each season (Christiansen and Dunham, 1972). Females sometimes divide a single clutch of eggs, ovipositing the eggs in two nests (Tuma, 1993). Eggs are elliptical, hard, and white, 24.0-28.5 mm in length and 13.5-16.5 mm in width.
The hatchling carapace is 21-30 mm long, and the width nearly equals the length. It is slightly keeled, and marginals 9 and 10 are the same height as or slightly lower than marginal 8. Cahn (1937) reported that elevation of the marginals first appears at a carapace length of about 67 mm.
Kinosternon flavescens is omnivorous. Mahmoud (1968) found the following percentages of frequency and volume, respectively, of food items in K. flavescens: Insecta 94.7, 27.8; Crustacea 99.2, 27.7; Mollusca 93.7, 23.5; Amphibia 91.2, 9.2; carrion 13.2, 3.2; and aquatic vegetation 37.2, 8.5. Turtles under 5 cm in carapace length fed predominantly on small aquatic insects, algae, and carrion, whereas those over 5 cm ate a greater variety of items. Yellow mud turtles are essentially bottom feeders but sometimes feed at the surface or on land. Their acute sense of smell and taste under water aids them in locating food.
With the onset of cold weather these turtles burrow into natural depressions, such as old stumpholes, and beneath shrubs, brushpiles, logs, or leaf litter. Some dig burrows in loose sandy soil; others hibernate in muskrat dens or in the mud at the bottom of pools. During the hottest parts of summer they seek out sheltered spots to aestivate.

IUCN Red List Status (1996)
Not listed.