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Montana Field Guides

Spiny Softshell - Apalone spinifera

Species of Concern
Native Species

Global Rank: G5
State Rank: S3

Agency Status

External Links

General Description
The eggs are hard and white with a smooth and spherical shape. The shell is thick and brittle, approximately 24-32 mm (0.94-1.26 in) in diameter. Clutch size can range from as few as 4 eggs to as many as 40 (typically 12-18), with eggs deposited in flask-shaped nests that are covered with soil (Webb 1962, Miller et al. 1989, Ernst et al. 1994, Hammerson 1999).

The carapace is olive to tan, with small dark circles, spots, or dashes, and a yellowish margin bordered by a black line. Carapace is approximately 3-4 cm (1.2-1.6 in) in length.

Juveniles have characteristics that are female-like, except the carapace coloration, which is male-like.

The shell is flattened (pancake-like), with flexible edges and covered with leathery skin. The tail is thick and long, with the vent well beyond the rear edge of the carapace. Small conical tubercles or “spines” are present on the front edge of the carapace above the neck. The snout is tubular and flexible, with a ridge along the inner margin of each nostril. This allows the species to remain beneath the surface with just the snout exposed. The lips are fleshy and cover sharp-edged jaws. Limbs are flat, and the toes are broadly webbed. Carapace coloration is olive-brown, brown, or grayish, with a cream or yellowish margin. The plastron is unmarked and cream to yellowish in coloration (Webb 1962, Ernst et al. 1994, Hammerson 1999, Stebbins 2003).

In mature males, the carapace has the texture of sandpaper, and marked with small dark spots or circles. The tail is thick and long, with the vent well beyond the rear edge of the carapace. In mature females, the carapace does not have the texture of sandpaper with more mottled or marked with blotches. Tubercles at the front edge of the carapace are more prominent than in males, and the tail is relatively short. Adult females can reach 54 cm (21.3 in) in carapace length (CL), while males are smaller by an average of 10 cm (3.9 in) and reach about 22 cm (8.7 in) in carapace length. For example, a study in southeastern Montana produced 14 males ranging from 14.8-21.6 cm (5.8-8.5 in) CL, weighing 290-730 g (10.23-25.75 oz), and 23 females ranging from 28.3-43.8 cm (11.1-17.2 in) CL, weighing 2,080-6,700 g (73.4-236.3 oz) (Gates 2005).

Diagnostic Characteristics
The Spiny Softshell (Apalone spinifera) differs from other Montana turtles by having a flattened and leathery shell that is soft and by the presence of a pointed snout with tubular nostrils. The Smooth Softshell (A. muticus), which occurs in the Missouri River in South Dakota and southern North Dakota (Hoberg and Gause 1989, Ballinger et al. 2000), differs from the Spiny Softshell by lacking the ridge on the inner margin of each tubular nostril and the absence of tubercles or spines along the front edge of the carapace (Ernst et al. 1994).

Species Range
Montana Range Range Descriptions

All Ranges
(Click legend blocks to view individual ranges)

Western Hemisphere Range


Range Comments
The Spiny Softshell is one of three North American turtle species formerly in the genus Trionyx that were moved to Apalone by Meylan (1987). Other authors (Webb 1990, Ernst et al. 1994, Hammerson 1999, Stebbins 2003) have retained the Spiny Softshell in Trionyx. Molecular data indicates a genetic dichotomy between populations of Spiny Softshell north and west of Louisiana and populations from the Gulf Coast in southeastern North America (Weisrock and Janzen 2000). The Spiny Softshell is divided into seven subspecies, six of which are present north of Mexico (Webb 1962, 1973, Ernst et al. 1994).

The Spiny Softshell is found from Montana east to southern Quebec, south in the west through northern and eastern Wyoming, eastern Colorado, New Mexico and Texas to northern Mexico, and east through the Midwest west of the Appalachian Mountains in the northeast, and throughout the Gulf region and southeastern United States to the Florida panhandle, to elevations of about 1,580 m (5,200 ft) (Stebbins 2003). It has been introduced in the Colorado-Gila River system of Arizona and in New Jersey (Webb 1973). There are disjunct populations in several areas around the periphery of the range.

The subspecies present in Montana is the Western Spiny Softshell, A. spinifera hartwegi (Conant and Goin 1948, Webb 1962, 1973, Ernst et al 1994). Populations in Montana are isolated from the remainder of the species and subspecies range, and merit genetic examination. In Montana, they are known from 25 counties east of the Continental Divide and two counties west of the Continental Divide. There is a paucity of records along the Missouri River at and below Fort Peck Reservoir, and few records from the Musselshell River in central Montana (Maxell et al. 2003, Werner et al. 2004). Available records suggest that the Missouri and Yellowstone populations within Montana are isolated from each other.

Maximum elevation: 1,158 m (3,799 ft) in Wheatland County (Kayhan Ostovar and Mike Burda, MTNHP POD 2023).

Observations in Montana Natural Heritage Program Database
Number of Observations: 1222

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

No migration has been documented in Montana. In Vermont, Spiny Softshell migrated about 3 km (1.9 mi) between riverine wintering sites and river mouth nesting sites near Lake Champlain. Migratory movements were most extensive in spring and fall (Graham and Graham 1997). Annual home range size for male Spiny Softshell in Arkansas was 784-2,310 m (2,572-7,579 ft) (average 1,750 m or 5,741 ft) of stream length, and 683-2,145 m (2,241-7,037 ft) (average 1,400 m or 4,593 ft) for females (Plummer et al. 1997, Hammerson 1999). During the active season, they were very mobile, and made movements on 85% of days.

The Spiny Softshell is primarily an animal of riverine systems, but also inhabits marshy creeks, bayous, oxbows, lakes, irrigation canals, and impoundments (Webb 1962, Ernst et al. 1994, Hammerson 1999, Stebbins 2003). A soft bottom in permanent bodies of water with some aquatic vegetation appears to be essential, and sandbars and/or mudflats, as well as partially submerged debris (trees, fallen logs, brush), are usually present. In shallow water, young Spiny Softshell bury themselves in soft sand and silt to seek refuge and concealment (Baxter and Stone 1985). In Iowa, females seemed to prefer open water more than males (Williams and Christiansen 1981). Eggs are laid in nests dug in open areas in sand, gravel, or soft soil near water (Baxter and Stone 1985, Ernst et al. 1994, Hammerson 1999, Stebbins 2003).

Habitat use by Spiny Softshell in Montana is probably similar to elsewhere in the range, but studies are lacking and there is little qualitative information available. They are encountered most often in the larger rivers and their tributaries. Adult males and females have been observed basking together on partially submerged logs in backwater sites of slow-moving water, on sandy and muddy riverbanks, and on partially submerged rocks in shallow water along major rivers. Hatchlings have been found in shallow water at the edge of rivers, burrowing into silty substrate with emergent vegetation present (Paul Hendricks, personal observation). A small-scale trapping and visual encounter survey conducted on a six-mile (9.7 km) stretch of the upper Tongue River in southeastern Montana concluded that the most successful trapping locations were near sandbar islands adjacent to pools with a soft organic bottom. Additionally, stretches of river with exposed boulders and basking logs produced the most visual observations (Gates 2005).

Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
Spiny Softshell forage in the water, often on the bottom in shallow with vegetation, and are considered generalist carnivores. Major foods include crayfish, aquatic insects (at least seven Orders), and fishes; mollusks, worms, isopods, amphibians, carrion, and vegetation are also taken (Webb 1962, Ernst et al. 1994, Hammerson 1999). The diet in an Iowa study (Williams and Christiansen 1981) was about 25% insects, 36.5% fish as carrion, 5.8% small fish as live prey, and 55% crayfish, with plant material in 61% of stomachs. This breakdown of categories appears representative for other states (Ernst et al. 1994). Prey may be chased, ambushed, or flushed and pursued. The diet in Montana has not been studied.

Because Spiny Softshell dehydrate quickly, they are seldom seen far from water. However, they will move overland when exposed to falling water levels (Williams and Christiansen 1981). They burrow into the bottoms of permanent water bodies, either shallow or relatively deep, approximately 0.5-7.0 m (1.6-23 ft), where they hibernate (Graham and Graham 1997, Plummer and Burnley 1997). Hibernation sites may occur within the summer home range or a few kilometers from summer nesting areas. Adults are active from April to October (usually May to September) in Kentucky, Tennessee, and Colorado (Robinson and Murphy 1978, Ernst et al. 1994, Hammerson 1999), and are similar elsewhere in the range (Webb 1962). Water temperatures of 12 °C (53.6 °F) appear to determine when animals enter or emerge from hibernation in Vermont (Graham and Graham 1997). Adults emerge earlier and remain active longer into fall, than do juveniles. The length of the active season increases with decrease in latitude (Webb 1962). The period of activity in Montana is poorly documented, with records from early June to late July (Hendricks and Reichel 1996b, Hendricks 1999a).

Egg predators include Striped Skunk (Mephitis mephitis), Spotted Skunk (Spilogale gracilis), Raccoon (Procyon lotor), Red Fox (Vulpes vulpes), and probably Coyote (Canis latrans); young Spiny Softshell are captured and eaten by predatory fish, wading birds, and Muskrat (Ondatra zibethicus) (Ernst et al. 1994, Hammerson 1999). Some individuals are caught by anglers using live or dead bait, and then killed. No information on predators is available from Montana, but some adults are incidentally captured and killed by anglers.

Reproductive Characteristics
Mating occurs shortly after emerging from winter dormancy, in April or May. Nesting may begin in late May and extend into August, but usually occurs in June and July in Tennessee and Colorado (Robinson and Murphy 1978, Hammerson 1999). Eggs are laid in flask-shaped burrows excavated in coarse sand or fine gravel, to depths of 10-25 cm (4-10 in). Colorado nests contained 15-39 eggs (Miller et al. 1989b, Hammerson 1999), but as few as 3 eggs have been reported in Indiana (Webb 1962). During the reproductive season, eggs may be laid in two clutches, but there is no evidence for production of multiple clutches throughout the species range (Robinson and Murphy 1978, Hammerson 1999). Eggs hatch in about 60-80 days. Most hatching occurs in August to September in Colorado. In some families of turtles, incubation temperature determines the sex of hatchlings, but this effect of incubation temperature does not appear to pertain to Spiny Softshell (Vogt and Bull 1982a). Some hatchlings may overwinter in the nest and emerge the following spring, although there is no solid evidence that this occurs (Ernst et al. 1994, Hammerson 1999).

Little information is available from Montana on any aspect of the reproductive biology of this species. A small juvenile with a carapace length of 4.0 cm (1.6 in) was captured in mid-July on the Missouri River (Paul Hendricks, personal observation). Individuals may live up to 50 years based on the relationship between growth rate and observed carapace size. Females mature at a carapace length of about 25 cm (10 in) or approximately 8-9 years of age. Males mature earlier at approximately 4-5 years when carapace length is about 16 cm (6.3 in) (Breckenridge 1955, Webb 1962). The oldest female of known age (a captive zoo animal) lived 25 years (Ernst et al. 1994). Nevertheless, little quantitative information is available on survival rate and longevity.

The following was taken from the Status and Conservation section for the Spiny Softshell account in Maxell et al. 2009.

At the time the comprehensive summaries of amphibians and reptiles in Montana (Maxell et al. 2003, Werner et al. 2004) were published, there were about 70 total records for Spiny Softshell from 13 counties. Records are scattered east of the Continental Divide along the Missouri River and tributaries between the confluence of the Musselshell River and Fort Benton. Also, low on the Marias River downstream from Tiber Reservoir, and along the Yellowstone River and tributaries between Edgar (Carbon County) and Glendive (Dawson County), including the Clark Fork of the Yellowstone, Bighorn, Tongue, and Powder rivers. Populations in parts of the Missouri River (especially the Wild and Scenic portion) appear to be robust, with 21 and 24 individuals observed opportunistically on each of two float trips between Coal Banks and Judith landings in July 2003 and 2004 (Paul Hendricks, personal observation). On the Tongue River near Brandenburg (Rosebud County), several basking adults were observed in three consecutive years (Hendricks 1999a). On a six-mile (9.7 km) stretch of the upper Tongue River, near Decker, a short, five-day trapping survey produced 37 Spiny Softshell captures at 14 of 30 trap locations without any recaptures, and an additional 60 individuals were seen basking while traversing the river (Gates 2005). This suggests a healthy population may be present in this region of the river. However, population density and trend estimates remain unavailable for any locality in Montana, including areas of recent surveys. In the Arkansas River of central Kansas, the population density of Spiny Softshell was estimated to be 500-700 individuals per river mile (Capron 1987), probably a value exceeding that in Montana. Connectivity of populations is unknown; the Missouri River population above Fort Peck appears to be isolated from the Yellowstone River population, and Spiny Softshell in the Musselshell River may be isolated from the remainder of the Missouri River population. All Spiny Softshell in Montana appear to be isolated from the remainder of the species range in the United States. There are no confirmed records from North Dakota; there is an old record from Fort Union, but the collection locality is uncertain (Maxell et al.2003), and the nearest records in the Missouri River are from southeastern South Dakota (Hoberg and Gause 1989, Ballinger et al. 2000). Status on the Marias River is also uncertain. Spiny Softshell were not reported by Mosimann and Rabb (1952) near the site of Tiber Reservoir prior to its flooding but have been seen in recent years far downstream nearer the confluence with the Missouri River. On the local scale, limited data from other states suggest this species is relatively sedentary, with most movements restricted to about 3 km (1.9 mi) of stream or river (Graham and Graham 1997, Plummer et al. 1997). Given the limited distance Spiny Softshell move over land, populations are vulnerable to habitat fragmentation, especially by dams or other water diversion projects. Risk factors relevant to the viability of populations of this species are likely to include habitat loss/fragmentation, dam construction, water diversion, pollutants (including herbicides and pesticides), accidental take during recreational fishing, mining of sand and gravel, and off- road vehicle use (Hammerson 1999). However, perhaps the greatest risk to maintaining viable populations of Spiny Softshell in Montana is the lack of baseline data on its distribution, status, habitat use, and basic biology (Maxell and Hokit 1999), which are needed to monitor trends and recognize dramatic declines when and where they occur. Few studies address or identify risk factors. Throughout much of its range, the Spiny Softshell has been sought for food (Carr 1952) and is sometimes killed because of the erroneous belief that Spiny Softshell are harmful to fish populations (Webb 1962). The impact of accidental and intentional take by fisherman in Montana is unknown.

  • Literature Cited AboveLegend:   View Online Publication
    • Ballinger, R.E., J.W. Meeker, and M. Thies. 2000. A checklist and distribution maps of the amphibians and reptiles of South Dakota. Transactions of the Nebraska Academy of Sciences 26:29-46.
    • Baxter, G.T. and M.D. Stone. 1985. Amphibians and reptiles of Wyoming. Second edition. Wyoming Game and Fish Department. Cheyenne, WY. 137 p.
    • Breckenridge, W. J. 1955. Observations on the life history of the soft-shelled turtle Trionyx ferox, with especial reference to growth. Copeia 1955:5-9.
    • Capron, M. 1987. Selected observations on south-central Kansas turtles. Kansas Herpetological Society Newsletter 67:13-15.
    • Carr, A.F. 1952. Handbook of turltles: the turtles of the United States, Canada, and Baja California. Cornell University Press, Ithaca, New York.
    • Conant, R. and C.J. Goin. 1948. A new subspecies of soft-shelled turtle from the central United States, with comments on the application of the name Amyda. Occassional Papers, Museum of Zoology, University of Michigan, No. 510, p. 1, map 1, pls. 1-2.
    • Ernst, C. H., R. W. Barbour, and J. E. Lovich. 1994. Turtles of the United States and Canada. Smithsonian Institution Press. Washington, D.C. 578 p.
    • Gates, M.T. 2005. Amphibian and reptile baseline survey: CX field study area Bighorn County, Montana. Report to Billings and Miles City Field Offices of Bureau of Land Management. Maxim Technologies, Billings, MT. 28pp + Appendices.
    • Graham, T. E. and A. A. Graham. 1997. Ecology of the eastern spiny softshell, Apalone spinifera spinifera, in the Lamoille River, Vermont. Chelonian Conservation and Biology 2(3): 363-369.
    • Hammerson, G.A. 1999. Amphibians and reptiles in Colorado. University Press of Colorado & Colorado Division of Wildlife. Denver, CO. 484 p.
    • Hendricks, P. 1999a. Amphibian and reptile survey of the Bureau of Land Management Miles City District, Montana. Montana Natural Heritage Program, Helena, MT. 80 p.
    • Hendricks, P. and J.D. Reichel. 1996b. Preliminary amphibian and reptile survey of the Ashland District, Custer National Forest: 1995. Montana Natural Heritage Program, Helena, MT. 79 p.
    • Hoberg, T., and C. Gause. 1989. Reptiles & amphibians of North Dakota. North Dakota Outdoors 55(1):7-18.
    • Maxell, B.A. and D.G. Hokit. 1999. Amphibians and reptiles. Pages 2.1– 2.30 In G. Joslin and H. Youmans, committee chairs. Effects of recreation on Rocky Mountain wildlife: a compendium of the current state of understanding in Montana. Committee on Effects of Recreation on Wildlife, Montana Chapter of the Wildlife Society.
    • Maxell, B.A., J.K. Werner, P. Hendricks, and D.L. Flath. 2003. Herpetology in Montana: a history, status summary, checklists, dichotomous keys, accounts for native, potentially native, and exotic species, and indexed bibliography. Society for Northwestern Vertebrate Biology, Northwest Fauna Number 5. Olympia, WA. 135 p.
    • Maxell, B.A., P. Hendricks, M.T. Gates, and S. Lenard. 2009. Montana amphibian and reptile status assessment, literature review, and conservation plan, June 2009. Montana Natural Heritage Program. Helena, MT. 643 p.
    • Meylan, P.A. 1987. The phylogenetic relationships of soft-shelled turtles (family Trionychidae). Bulletin of the American Museum of Natural History 186(1): 1-101.
    • Miller, K., G.C. Packard, and M.J. Packard. 1989b. Life history notes: Trionyx spiniferus. Herpetological Review 20(2): 56.
    • Miller, K., G.F. Birchard, M.J. Packard, and G.C. Packard. 1989a. Trionyx spiniferus (spiny softshell turtle). Fecundity. Herpetological Review 20(2): 56.
    • Mosimann, J.E. and G.B. Rabb. 1952. The herpetology of Tiber Reservoir Area, Montana. Copeia(1): 23-27.
    • Plummer, M. V., and J. C. Burnley. 1997. Behavior, hibernacula, and thermal relations of softshell turtles (Trionyx spiniferus) overwintering in a small stream. Chelonian Conservation and Biology 2:489-493.
    • Plummer, M.V., N.E. Mills, and S.L. Allen. 1997. Activity, habitat, and movement patterns of softshell turtles (Trionyx spiniferus) in a small stream. Chelonian Conservation Biology 2:514-520.
    • Robinson, K.M., and G.G. Murphy. 1978. The reproductive cycle of the eastern spiny softshell turtle (Trionyx spiniferus spiniferus). Herpetologica 34(2): 137-140.
    • Stebbins, R. C. 2003. A field guide to western reptiles and amphibians. 3rd Edition. Houghton Mifflin Company, Boston and New York. 533 p.
    • Vogt, R.C. and J.J. Bull. 1982a. Genetic sex determination in the spiny softshell Trionyx spiniferus (Testudines: Trionychidae)? Copeia 1982: 699-700.
    • Webb, R.G. 1962. North American soft-shelled turtles (Family Trionychidae). University of Kansas Publications of the Museum of Natural History 13:429-611.
    • Webb, R.G. 1973. Trionyx spiniferus. Catalogue of American Amphibians and Reptiles 140.1-140.4.
    • Webb, R.G. 1990. Trionyx. Catalogue of American Amphibians and Reptiles 487.1-487.7.
    • Weisrock, D.W. and F.J. Janzen. 2000. Comparative molecular phylogeography of North American softshell turtles (Apalone): implications for regional and wide-scale historical evolutionary forces. Molecular Phylogenetics and Evolution 14(1): 152-164.
    • Williams, T.A. and J.L. Christiansen. 1981. The niches of two sympatric softshell turtles, Trionyx muticus and Trionyx spiniferus, in Iowa. Journal of Herpetology 15: 303-308.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
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    • Brunson, R.B. 1955. Check list of the amphibians and reptiles of Montana. Proceedings of the Montana Academy of Sciences 15: 27-29.
    • Bull, J.J. and R.C. Vogt. 1979. Temperature-dependent sex determination in turtles. Science 206: 1186-1188.
    • Burghardt, G.M., B. Ward, and R. Rosscoe. 1996. Problem of reptile play: environmental enrichment and play behaviour in a captive Nile soft-shelled turtle, Trionyx triunguis. Zoo Biology 15(3): 223-238.
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    • Cochran, P.A. 1986b. Some observations on the herpetofauna of the University of Wisconsin – Madison Campus. Bulletin of the Chicago Herpetological Society 21(1-2): 138-141.
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