Tinkle and Webb, 1955
Flattened musk turtle
Recognition
The oval carapace (to 11.5 cm) is wide and very flattened. Its sides always slope at an angle greater than 100°, and in juveniles the mean angle/height ratio is about 9.5:1. There is a blunt middorsal keel, and the posterior marginals are serrated. Each vertebral overlaps the one behind (vertebrals are juxtaposed). The 1st is very long, and never touches the 2nd marginals; the other four vertebrals are broader than long, and the 5th is posteriorly expanded. The carapace is yellowish brown to dark brown with small, dark-brown or black spots or streaks and dark seams. The immaculate pink to yellowish brown plastron contains a single gular scute, and has an indistinct hinge between the pectoral and abdominal scutes. There is a shallow posterior notch. The plastral formula is: an > abd > pect > fem >< hum > gul. The head is moderate with a projecting tubular snout and a slightly hooked (sometimes notched) upper jaw. The rostral shield is furcated posteriorly, and there are two pairs of chin barbels. Fine black mottling is present on the olive head, and dark bars on the jaws. A yellow stripe from the nostril to the orbit may occur on some individuals. Other skin is olive with fine black mottling.
Males have thick, long, spine-tipped tails with the vent posterior to the carapacial rim, and roughened patches of scales on their thighs and crura.
Distribution
Sternotherus depressus is restricted to the Black Warrior River system in west-central Alabama.
Habitat
Clear, rock-bottomed to sandy, permanent streams above the fall line seem to be the preferred habitat.
Natural History
Tinkle (1958a) thought this species matured in four years; females a carapace length of 9-10 cm, males at about 7.5 cm. However, Close (in Mount, 1981) examined a large series of flattened musk turtles, and though that males require 4-6 years to mature at 6,0-6.5 cm carapace length, and females 6-8 years at 7.0-7.5 cm. The reproductive cycles of both sexes are unknown.
Estridge (in Mount, 1975) reported a female laid an oblong (32.0 x 16.4 mm) brittle-shelled egg in June which hatched in October. The hatchling had the following carapacial measurements: length, 25 mm; width, 20 mm; height 7.8 mm.
The food consists mostly of clams, snails, insects, crayfish, arachnids, and isopods. Older specimens often develop enlarged heads, presumably correlated with a mollusk diet.
Remark
Sternotherus depressus was originally described by Tinkle and Webb (1955) as a full species; however, Wermuth and Mertens (1961) and Ernst and Barbour (1972) designated it a subspecies of the closely related S. minor. Specimens intermediate between these species exist, but are probably interspecific hybrids rather than intergrades. Recent morphological studies and studies of the electrophoretic properties of proteins of these two turtles have shown them to be closely related but distinct species (Iverson, 1977b; Seidel and Lucchino, 1981; Seidel et al., 1981; Ernst et al., 1988b). Ernst et al. (1988b) showed these "intermediate" populations to be S. depressus. Although some individuals from western Alabama have head and neck patterns (characters quite variable in kinosternid turtles) similar to those in S. m. peltifer, carapacial configuration clearly indicates they are S. depressus.
IUCN Red List Status (1996)
Vulnerable (B1+2c).