(Gray, 1856)
Razorback musk turtle
Recognition
The deep, steeply sloping, oval carapace (to 16 cm) has a prominent medial keel and is slightly serrated posteriorly; each vertebral scute usually overlaps the one behind it. This high-peaked shell is triangular when viewed from the front; its sides always slope at an angle less than 100°. No dorsolateral keels are present on adults. The 1st vertebral scute is long and narrow but flared anteriorly; however, it never touches the 2nd marginal scutes. The 2nd vertebral varies from longer than broad, to as broad as long, or broader than long; the last three vertebrals are usually broader than long, and the last is laterally expanded. Carapacial scutes are light brown to orange, with dark spots or radiating streaks and dark posterior borders on each; this pattern usually fades with age. The immaculate yellow plastron lacks a gular scute and has only 10 instead of the normal 11 scutes found in Kinosternon and Sternotherus. An indistinct hinge is located between the pectoral and abdominal scutes, and there is a slight anal notch. The plastral formula is: an > abd > pect > hum >< fem. The head is moderate with a protruding tubular snout and a slightly hooked upper jaw. The rostral shield is deeply furcated posteriorly, and there is usually only one pair of chin barbels. All skin is gray to light brown or pink, with small dark spots; the jaws are tan with dark streaks.
The karyotype consists of 56 chromosomes (26 macrochromosomes, 30 microchromosomes): 16 metacentric and submetacentric, 8 subtelocentric, and 32 acrocentric and telocentric (Stock, 1972; Killebrew, 1975b).
Males have thick, long, spine-tipped tails with the vent located posterior to the carapacial rim, and roughened patches of scales (vinculae) on their thighs and crura.
Distribution
Sternotherus carinatus ranges from southeastern Oklahoma, central Arkansas, and Mississippi south to the Gulf of Mexico; the range is almost completely within the Gulf Coastal Plain.
Habitat
This species lives in rivers, slow streams, and swamps. Little current, soft bottoms, abundant aquatic vegetation, and some basking sites are the preferred conditions.
Natural History
Females mature at a carapace length of about 10 cm, which is reached in 4-5 years; males at 10-12 cm, in 5-6 years. Spermatogenesis begins in June and peaks by mid-August when the testes attain maximum size (Mahmoud and Klicka, 1972). During the last half of August though the middle of September the testes shrink as mature sperm are released to the epididymides. Testes size continues to decline through December when the testes weigh the least. No spermatogenesis occurs from January to April, but mature sperm descend into the vas deferens in March and April. In females, follicular growth proceeds slowly from September to November, and possibly also from December through February (Mahmoud and Klicka, 1972). In March and April follicles are yolked and enlarge, and during May and June grow at their fastest rate. Ovulation and oviposition also occur then. The largest corpora lutea are present when eggs are still in the oviducts, but begin to degenerate to corpora albicantia shortly after oviposition. There is no significant follicular growth during July and August.
Courtship and mating occur in the spring, and the acts are identical to those of Sternotherus odoratus (which see for details).
Presumably, nesting occurs from April through June, as females with oviducal eggs have been found during this period. At least two clutches of two to four white, elongated, brittle-shelled eggs are laid each year. Hatchlings emerge in August and September with carapace lengths of 23-31 mm and often three carapacial keels.
S. carinatus is omnivorous, feeding on insects, crustaceans, snails, clams, amphibians, and aquatic plants.
S. carinatus is a habitual basker; a full sunlight position on steeply angled branches of small diameter was recorded in about 74% of the observations by Lindeman (1996c).
Remark
Seidel and Lucchino (1981) electrophoretically examined 11 protein systems (17 loci) and discriminantly analyzed 15 morphological characters in a study of speciation among S. carinatus, S. minor and S. depressus, and found S. carinatus to be strongly divergent from the other two species.
IUCN Red List Status (1996)
Not listed.