| Sternotherus | |
|---|---|
 | |
| HatchlingSternotherus odoratus (eastern musk turtle) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Testudines |
| Suborder: | Cryptodira |
| Family: | Kinosternidae |
| Subfamily: | Kinosterninae |
| Genus: | Sternotherus Bell inGray, 1825[1] |
| Species | |
6 extant, 1 extinct., see text | |
Sternotherus is a genus of turtles in thefamilyKinosternidae including six species commonly known asmusk turtles. The genus is endemic toNorth 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. Thecarapace 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. Theplastron 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 areomnivorous and opportunistic generalist in their diet, although inclining toward being carnivorous, withmollusks (gastropods andbivalves) 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 areoviparous 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.[2]: 471–472, 511–535 pp.
The generic nameSternotherus is Greek meaning hinged breast or chest, referring to the hingedplastron.[3] The trivial names, or specific epithets include:carinatus – Latin for keeled in reference to the shape of thecarapace;[4]depressus – Latin for pressed down or low also referring to the shape of the carapace;[5]intermedius – Latin for intermediate, historically believed to be a hybrid from betweenS. minor andS. peltifer;[6]minor – Latin referencing its relatively small size compared toS. carinatus;[7]odoratus – Latin for having an odor, referring the smell of the musk produced by its scent glands;[8]peltifer – Latin meaning bearing a small shield, in reference to the small size of the scutes on the bridge the species.[2]: 647–648 pp. [7]
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Sternotherus is one of four genera in the familyKinosternidae 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 subfamilyKinosterninae within the family Kinosternidae. In the past some taxonomist placedSternotherus in the synonymy of the genusKinosternon[9][10] but they are generally regarded as two separate genera with six species currently (2022) recognized in the genusSternotherus.[11]
| Extant Species | Common name | Image |
|---|---|---|
| Sternotherus carinatus | razor-backed musk turtle |  |
| Sternotherus depressus | flattened musk turtle |  |
| Sternotherus intermedius | intermediate musk turtle | .jpg) |
| Sternotherus minor | loggerhead musk turtle |  |
| Sternotherus odoratus | eastern musk turtle[17] |  |
| Sternotherus peltifer (H.M. Smith &Glass, 1947)[18] | stripeneck musk turtle | .jpg) |
Fossil species
Nota bene: Abinomial authority in parentheses indicates that the species was originally described in a genus other thanSternotherus.
Turtles in the genusSternotherus are very similar to the Americanmud turtles in the genusKinosternon, but tend to have a moredomedcarapace, with a distinctive keel down the center of it.Sternotherus odoratus typically grows to only 8–14 cm (3.1–5.5 in) in straight carapace length at full maturity, with females often being larger than males.
The genusSternotherus is endemic to North America. It occurs in the approximant eastern third of the US and extreme southeastOntario, Canada. The eastern musk turtle (S. odoratus), the most wide-ranging species of the genus, occurs in southernMaine, south toFlorida, west into easternTexas,Oklahoma, andKansas, and north to southeastWisconsin, southernMichigan, and theGreat Lakes region of southern Ontario. It is generally absent from higher elevations in theAppalachian 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-centralAlabama in theBlack Warrior River basin above thefall line, and the intermediate musk turtle (S. intermedius) is found in southeastern Alabama and adjacent areas of theFlorida panhandle in theChoctawhatchee,Conecuh,Yellow,Pea,Blackwater, andEscambia rivers. The razor-backed musk turtle (S. carinatus) occurs throughoutLouisiana, and neighboring areas ofMississippi,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 easternTennessee with marginal records fromNorth Carolina, andVirginia.[20][6]
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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. Anontogenetic change in diet occurs and adults shift to an omnivorous diet with a high percentage of mollusk. Food items include mollusks (gastropods andbivalves), 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).[2]: 513, 516, 523, 533 pp. [21][22]
The razor-backed (S. carinatus) and eastern musk turtles (S. odoratus) are known to be bottom feeders, often searching with the neck extended and probing the mud and sand with their heads.Olfaction is probably important in the location and selection of food items. However, musk turtles occasionally feed at the surface and are also known to eat out of the water. Eastern musk turtles (S. odoratus) have occasionally been observed leaving the water at dusk to feed on slugs on land. Some larger adults develophypertrophied head musculature and expanded crushing surfaces on both the upper and lower jaws that aid in eating mollusk. One study concluded razor-backed (S. carinatus) and eastern musk turtles (S. odoratus) were "euryphagous with food preferences directly related to the availability of food."[22]: 304 p. Another study found the diet of the eastern musk turtle (S. odoratus) varied seasonally and males ate more insects and females more snails.[23] Digestive turnover rates, from ingestion to defecation, of 49 hours (S. odoratus) to 57 hours (S. minor, S. peltifer) have been reported, although temperatures may influence these times.[2]: 513, 516, 523, 533 pp. [24][22]
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Sternotherus are largely aquatic, but some species bask frequently, and may occasionally leave the water to forage and lay eggs. Fallen logs and deadwood submerged and emerging from the water are important for shelter and basking sites for all species ofSternotherus. Habitat preferences varies among some species. The eastern musk turtle (S. odoratus) tends to be generalist and may occur in almost any body of water, as are loggerheads (S. minor) to a lesser extent, although water with slow or no currents, soft bottoms, and shelter in the form of logs and rocks are usually preferred over very deep water and swift currents. Eastern musk turtles have been found at depths of 9 meters but, shallower water (ca. 1 meter), are more typical. Brackish water is usually avoided. Depths of 0.5–1.5 meters are typical for loggerheads (S. minor), but they have been found at 13 meters.[2]: 520 p. [25] The razor-backed musk turtle (S. carinatus) favors the relatively deeper waters of rivers, creeks, bayous, and associated oxbow lakes, backwater swamps, and floodplains where slower currents and soft substrates are found.[2]: 511 p. The stripe-necked musk turtle (S. peltifer) arelotic, preferring the currents of rivers and streams although they can be abundant in lakes and impoundments along these waterways as well.[2]: 520 p. The flattened musk turtle (S. depressus) is an inhabitant of clear, rocky to sandy bottom creeks and streams above the fall line, typically 1.5 meters or less in depth, taking shelter under logs and rocks, or burrowing in the sand.[2]: 515 p. The intermediate musk turtle (S. intermedius) was regarded as a hybrid betweenS m. minor andS. m. peltifer as recently as 2017, and few if any studies specifically examining the ecology of the species have been published (as of 2022).
In one ecological study ofkinosternid turtles conducted over five years inOklahoma, permanent bodies of lotic (moving) water in wooded areas such as large rivers and creeks were the favored habitats of both razor-backed (S. carinatus) and eastern musk turtles (S. odoratus), however,S. carinatus was generally found in deeper water. No sexual, age, or seasonal differences were observed in habitat selection other than juveniles preferred shallower water than adults. The two species were strictly aquatic and terrestrial migrations occurred only during the breeding season. When inactive, both specie hid under rocks, logs, and overhanging banks, but did not show the burrowing proclivities thatKinosternon did. Turtles were found in abundance in quiet waters where submerged and floating vegetation such as algae,Nasturtium,Polygonum,Myriophyllum,Najas, andPotamogeton formed in mats and provided food and suitable shelter. Light intensity,pH levels, and transparency of water were examined, although it was concluded they were probably not directly limiting factors for the turtles, but did affect the distribution of vegetation and prey which provided food for the turtles.[26]
Sternotherus is a highly aquatic genus. But some species, like thecommon musk turtle, are known to bask on fallen trees and coarse woody debris on shorelines.[2] The thermal activity range and annual activity period was longer forSternothaerus thanKinosternon[26]
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| Other | |
