Sternotherus is a genus of turtles in the family Kinosternidae including six species commonly known as musk turtles. The genus is endemic to North America, occurring in the eastern third of the US and southeast Ontario, Canada. Musk glands positioned near the bridge of the shell can produce foul smelling secretions when the turtles are threatened, although gentle handling does not normally provoke a response. Sternotherus are moderately small turtles, with the largest species in the genus, the razor-backed musk turtle (S. carinatus), attaining a maximum of 17.6 cm. in shell length. The carapace is characteristically oval and domed (an exception being the flattened musk turtle, S. depressus), with most species having one or three keels on the back which may become smoother and obscure with age in some species. Musk turtles are generally drab in color, mostly black, gray, brown, olive, or ocher, which aid in camouflaging them in their natural habitats. The head is relatively large and stout, marked with spots, streaks, or strips. The plastron has only 10 or 11 scutes, as opposed to 12, a more common condition in North American turtles. The tail is short, with males having a horny claw like tip.
Sternotherus are largely aquatic, however some species frequently bask on fallen logs or rocks emerging from the water, and eastern musk turtles (S. odoratus) occasionally leave the water to forage. Sternotherus are omnivorous and opportunistic generalist in their diet, although inclining toward being carnivorous, with mollusks (gastropods and bivalves) and insects making up a significant percentage of their diet. Some older adults develop large musculature on the head and expanded, crushing jaw surfaces aiding in the consumption of mollusk. Musk turtles are oviparous with females producing one to six clutches a year. The typical clutch size is two to four eggs, although clutches may range from one to 13. The sex of the hatchlings is determined by the incubation temperature. The eggs are deposited in shallow nest excavated on the banks or in woodlands a few meters from the water. Eggs may be laid singly, or in groups, and some species are known to share communal nesting areas.Ernst, Carl, H. and Jeffrey E. Lovich. 2009. Turtles of the United States and Canada, 2nd. Ed. The Johns Hopkins University Press. Baltimore, MD. xii, 827 pp.
Etymology The generic name Sternotherus is Greek meaning hinged breast or chest, referring to the hinged plastron.Zug, George. 1986. Sternotherus. Catalogue of American Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles. 397:1-3. The trivial names, or specific epithets include: carinatus – Latin for keeled in reference to the shape of the carapace;Iverson, John B. 1979. Sternotherus carinatus. Catalogue of American Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles. 226:1-2. depressus – Latin for pressed down or low also referring to the shape of the carapace;Iverson, John B. 1977. Sternotherus depressus. Catalogue of American Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles. 194: 1-2. intermedius – Latin for intermediate, historically believed to be a hybrid from between S. minor and S. peltifer;Scott, Peter A., Travis C. Glenn, and, Leslie J. Rissler. 2017. Resolving taxonomic turbulence and uncovering cryptic diversity in the musk turtles (Sternotherus) using robust demographic modeling. Molecular Phylogenetics and Evolution. 120: 1-15. minor – Latin referencing its relatively small size compared to S. carinatus;Iverson, John B. 1977. Sternotherus minor. Catalogue of American Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles. 195: 1-2. odoratus – Latin for having an odor, referring the smell of the musk produced by its scent glands;Reynolds, Samuel L. and Michael E. Seidel. 1982. Sternotherus odoratus. Catalogue of American Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles. 287: 1-4. peltifer – Latin meaning bearing a small shield, in reference to the small size of the scutes on the bridge the species.
Taxonomy
Sternotherus is one of four genera in the family Kinosternidae including: narrow-bridged musk turtles (Claudius), American mud turtles (Kinosternon), giant musk turtles (Staurotypus), and musk turtles (Sternotherus). Sternotherus are closely related, similar in appearance, and sympatric in much of their range with some species of mud turtles (Kinosternon), and the two genera constitute the subfamily Kinosterninae within the family Kinosternidae. In the past some taxonomist placed Sternotherus in the synonymy of the genus KinosternonIverson, John B., 1991. Phylogenetic hypotheses for the evolution of modern kinosternine turtles. Herpetological Monographs, No. 5: 1-27.Iverson, John B. 1992. A Revised Checklist with Distribution Maps of the Turtles of the World. Green Nature Books Homestead, Florida. 363 pp. but they are generally regarded as two separate genera with six species currently (2022) recognized in the genus Sternotherus.Uetz, Peter, Paul Freed, Aguilar, R. & Hošek, J. (eds.) (2021) The Reptile Database: http://www.reptile-database.org, (accessed March 5, 2022) +Sternotherus Bell, T. in Gray, John Edward. 1825. A synopsis of the genera of reptiles and Amphibia, with a description of some new species. Annals of Philosophy 10: 193-217. – musk turtlesExtant SpeciesCommon nameImageSternotherus carinatus Gray, John Edward. 1855 . Catalogue of Shield Reptiles in the Collection of the British Museum. Part I. Testudinata (Tortoises). Taylor and Francis, London, 79 pp.razor-backed musk turtleSternotherus depressus Tinkle, Donald W., and Robert G. Webb 1955. A new species of Sternotherus with a discussion of the Sternotherus carinatus complex (Chelonia, Kinosternidae). Tulane Studies in Zoology 3 (3): 53.flattened musk turtleSternotherus intermedius intermediate musk turtleSternotherus minor Agassiz, Louis 1857. Contributions to the Natural History of the United States of America. Vol. 1. Little, Brown & Co., Boston, 452 pp.loggerhead musk turtleSternotherus odoratus Latreille, Pierre André. 1801 . In: C.N.S. Sonnini de Manoncourt and P.A. Latreille. Histoire Naturelle des Reptiles, avec Figures Déssinnées d'après Nature. Détérville, Paris, Vol. 1. xx + 280 p.eastern musk turtleCrother, Brian I. (ed.). 2017. Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico, with Comments Regarding Confidence in Our Understanding. SSAR Herpetological Circular 43, 1–102 pp. [see page 90] Sternotherus peltifer Smith, Hobart M. & Bryan P. Glass. 1947. A new musk turtle for southeastern United States. Journal of the Washington Academy of Sciences 37 (1): 22-24.stripeneck musk turtle Fossil species †Sternotherus palaeodorus
Nota bene: A binomial authority in parentheses indicates that the species was originally described in a genus other than Sternotherus.
Description Turtles in the genus Sternotherus are very similar to the American mud turtles in the genus Kinosternon, but tend to have a more domed carapace, with a distinctive keel down the center of it. Sternotherus odoratus typically grows to only in straight carapace length at full maturity, with females often being larger than males.
Distribution
The genus Sternotherus is endemic to North America. It occurs in the approximant eastern third of the US and extreme southeast Ontario, Canada. The eastern musk turtle (S. odoratus), the most wide-ranging species of the genus, occurs in southern Maine, south to Florida, west into eastern Texas, Oklahoma, and Kansas, and north to southeast Wisconsin, southern Michigan, and the Great Lakes region of southern Ontario. It is generally absent from higher elevations in the Appalachian Mountains.
The other species in the genus largely occur within the southern regions of the eastern musk turtle's range. Two species have relatively limited distributions, the flattened musk turtle (S. depressus) is endemic to north-central Alabama in the Black Warrior River basin above the fall line, and the intermediate musk turtle (S. intermedius) is found in southeastern Alabama and adjacent areas of the Florida panhandle in the Choctawhatchee, Conecuh, Yellow, Pea, Blackwater, and Escambia rivers. The razor-backed musk turtle (S. carinatus) occurs throughout Louisiana, and neighboring areas of Mississippi, Arkansas, Oklahoma, and Texas. The loggerhead musk turtle (S. minor) is found in extreme southeast Alabama, Georgia, and northern Florida. The stripe-necked musk turtle (S. peltifer) predominantly occurs in Alabama and Mississippi with some peripheral records from Georgia, and Louisiana, and ranging into northern watersheds in eastern Tennessee with marginal records from North Carolina, and Virginia.Powell, Robert, Roger Conant, and Joseph T. Collins 2016. Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America, Fourth Edition. Boston and New York: Houghton Mifflin Harcourt. xiii + 494 pp. [pages 227-229]
Diet
Sternotherus are omnivorous. The loggerhead (S. minor) and stripe-necked musk turtle (S. peltifer) have been described as opportunistic generalist tending toward carnivory. Mollusk make up a significant portion of the diet in all species, particularly adults. Juveniles and sub-adults (under 5 cm.) feed on a higher percentage of aquatic insects, algae, and carrion. An ontogenetic change in diet occurs and adults shift to an omnivorous diet with a high percentage of mollusk. Food items include mollusks (gastropods and bivalves), insects (including larva, adults, aquatic and terrestrial), crustaceans (crayfish and crabs), worms (earthworms and leeches), amphibians (tadpoles and small frogs), carrion, filamantous green algae, parts of vascular plants and seeds (e.g. Prunus, Sambucus, Ulmus, Podostemum). Some novel and less common documented food items include spiders, millipedes, small fish and fish eggs, isopods, and small turtles. The flattened musk turtle (S. depressus) is known to feed on introduced Asian clams (Corbicula maniliensis).Marion, Ken R., William A. Cox, and Carl H. Ernst. 1991. Prey of the flattened musk turtle, Sternotherus depressus. Journal of Herpetology 25.3 (1991): 385-387Mahmoud, I. Y. 1968. Feeding behavior in kinosternid turtles. Herpetologica, 24(4), 300-305.