Spiny Softshell - Apalone spinifera
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 inches) 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 inches) in length.
JUVENILES AND ADULTS:
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 this 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 is 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 inches) in carapace length (CL), while males are smaller by an average of 10 cm (3.9 inches) and reach about 22 cm (8.7 inches) in carapace length. For example, a study in southeastern Montana produced fourteen males ranging from 14.8-21.6 cm (5.8-8.5 inches) CL (290-730 grams), and 23 males ranging from 28.3-43.8 cm (11.1-17.2 inches) CL (2080-6700 grams) (Gates 2005).
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).
Western Hemisphere Range
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:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
(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 (2572-7579 ft) (average 1,750 m (5741 ft)) of stream length, and 683-2,145 m (2241-7037 ft) (average 1,400 m (4593 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 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:
- 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);
- Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
- 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: mtnhp.org/requests
) 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.
- 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.
- Commonly Associated with these Ecological Systems
Wetland and Riparian Systems
- Occasionally Associated with these Ecological Systems
Recently Disturbed or Modified
Wetland and Riparian Systems
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 (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 km 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.
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 inches). 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 inches) 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 inches) or approximately 8-9 years of age. Males mature earlier at approximately 4-5 years when carapace length is about 16 cm (6.3 inches) (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 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?
- [DCC] Decker Coal Company. 1998. 1997 Consolidated annual progress report. Decker Coal Company West, North and East Pits. Decker, MT.
- [OEA] Olson Elliot and Associates Research. 1985. 1983-1984 Wildlife monitoring report for the CX Ranch project. Olson Elliot and Associates Research. Helena, MT.
- [PRESI] Powder River Eagle Studies Incorporated. 1998b. Spring Creek Mine 1997 wildlife monitoring studies. Powder River Eagle Studies Incorporated. Gillete, WY.
- Allen, E.R. 1982. Life history notes, Testudines, Trionyx ferox (Florida softshell). Size. Herpetological Review 13:49.
- Allen, J. A. 1874. Notes on the natural history of portions of Dakota and Montana Territories, being the substance of a report to the Secretary of War on the collections made by the North Pacific Railroad Expedition of 1873. Proceedings of the Boston Society of Natural History. pp. 68-70.
- Audubon, M.R. (ed.). 1960. Audubon and his journals. Volume 2. Dover Publications Incorporated. New York, NY.
- Benson, K.R. 1978. Herpetology of the Lewis and Clark expedition 1804-1806. Herpetological Review 9(3): 87-91.
- Black, J.H. and J.N. Black. 1971. Montana and its turtles. International Turtle and Tortoise Society 1971(May-July): 10-11, 34-35.
- Black, J.H. and R. Timken. 1976. Endangered and threatened amphibians and reptiles in Montana. p 36–37. In R.E. Ashton, Jr. (chair). Endangered and threatened amphibians and reptiles in the United States. Society for the Study of Amphibians and Reptiles Herpetological Circular 5: 1-65.
- Breckenridge, W.J. 1960. A spiny soft-shelled turtle nest study. Herpetologica 16(4): 284-285.
- Brooks, R. J., D. A Galbraith, E. G. Nancekivell, and C. A. Bishop. 1988. Developing management guidelines for snapping turtles. In: R.C. Szaro, K.E. Severson, and D.R. Patton, technical coordinators. pp. 174-179. Management of amphibians, reptiles, and small mammals in North America. General Technical Report RM-166. U.S. Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado.
- Brooks, R. J., G. P. Brown, and D. A. Galbraith. 1991. Effects of a sudden increase in natural mortality of adults on a population of the common snapping turtle (Chelydra serpentina). Canadian Journal of Zoology 69: 1314-1320.
- Brown, G. P. and R. J. Brooks. 1994. Characteristics of and fidelity to hibernacula in a northern population of snapping turtles, Chelydra serpentina. Copeia 1: 222-226.
- Brown, G.P. and R.J. Brooks. 1993. Sexual and seasonal differences in activity in northern population of snapping turtles, Chelydra serpentina. Herpertologica 49(3): 311-318.
- Brunson, R.B. 1955. Check list of the amphibians and reptiles of Montana. Proceedings of the Montana Academy of Sciences 15: 27-29.
- 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.
- Burroughs, R. D. 1961. Natural history of the Lewis and Clark expedition. Michigan State University Press, East Lansing. 340 p.
- Carlson, J. (Coordinator, Montana Animal Species of Concern Committee). 2003. Montana Animal Species of Concern January 2003. Helena, MT: Montana Natural Heritage Program and Montana Fish, Wildlife, and Parks. In Press. 12p.
- Carpenter, C.C. 1981. Life history notes: Trionyx spiniferus. Herpetological Review 12(3): 82.
- Carpenter, K. 1981. Preneural in the evolution of Trionyx. Copeia2: 456-457.
- 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.
- Cochran, P.A. and D.R. McConville. 1983. Feeding by Trionyx spiniferus in backwaters of the upper Mississippi River. Journal of Herpetology 17(1): 86-88.
- Cochran, P.A. and J.D. Lyons. 1986. New distributional records for Wisconsin (USA) amphibians and reptiles. Transactions of the Wisconsin Academy of Sciences Arts and Letters 74(0): 138-141.
- Coldiron, R.W. 1974. Possible funtions of ornament in labyrinthodont amphibians. Occaisional Papers of Museum of Natural History University of Kansas 33:1-19.
- Congdon, J .D., A. E. Dunham and R. C. Van Loben Sels. 1994. Demographics of common snapping turtles (Chelydra serpentina): implications for conservation and management of long-lived organisms. American Zoologist 34: 397-408.
- Congdon, J. D., G. L. Breitenbach, R. C. Van Loben Sels, and D. W. Tinkle. 1987. Reproduction and nesting ecology of snapping turtles (Chelydra serpentina) in southeastern Michigan (USA). Herpetologica 43(1): 39-54.
- Cope, E.D. 1875. Check-list of North American Batrachia and Reptilia; with a systematic list of the higher groups, and an essay on geographical distribution. Based on the specimens contained in the U.S. National Museum. U.S. Natioanl Museum Bulletin 1: 1-104.
- Coues, E. and H. Yarrow. 1878. Notes on the herpetology of Dakota and Montana. Bulletin of the U.S. Geological Geographic Survey of the Territories 4: 259-291.
- Crother, B.I. (ed.) 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico. SSAR Herpetological Circular No. 37:1-84.
- Daigle, C., P. Galois, and Y. Chagnon. 2002. Nesting activities of an eastern spiny softshell turtle, Apalone spinifera. Canadian Field Naturalist 116:104-107.
- Dalrymple, G.H. 1977. Intraspecific variation in the cranial feeding mechanism of turtles of the genus Trionyx (Reptilia, Testudines, Trionychidae). Journal of Herpetology 11:255-285.
- Dalrymple, G.H. 1979. Packaging problems of head retraction in trionychid turtles. Copeia 1979:655-660.
- Day, D. 1989. Montco Terrestrial Wildlife Monitoring Report. Unpublished report for Montco, Billings, Montana.
- Day, D., P.J. Farmer, and C.E. Farmer. 1989. Montco terrestrial wildlife monitoring report December, 1987 - July, 1989. Montco, Billings, MT, and Western Technology and Engineering, Inc. Helena, MT.
- DeRosa, C.T. 1978. A comparison of orientation mechanisms in aquatic, semi-aquatic and terrestial turtles (Trionyx spinifer, Chrysemys picta and Terrapene c. carolina). Ph.D. Dissertation, Miami University 99p.
- DeRosa, C.T. and D.H. Taylor. 1980. Homeward orientation mechanisms in three species of turtles (Trionyx spinifer, Chrysemys picta, and Terrapene carolina). Behavioral Ecology and Sociobiololgy 7(1):15-23.
- DeRosa, C.T. and D.H. Taylor. 1982. A comparison of compass orientation mechanisms in three turtles (Trionyx spinifer, Chrysemys picta, and Terrapene carolina). Copeia 1982: 394-399.
- Drought, J.F. 1987b. Testudines. Trionyx spiniferus spiniferus (eastern spiny softshell). Herpetological Review 18(1): 21.
- Dunson, W.A. 1960. Aquatic respiration in Trionyx spinifer asper. Herpetologica 16(4): 277-283.
- Dunson, W.A. 1967. Relationship between length and weight in the spiny softshell turtle. Copeia 1967: 483-485.
- Fitch, H.S. and M.V. Plummer. 1975. A preliminary ecological study of the soft-shelled turtle Trionyk muticus in the Kansas River. Israel Journal of Zoology 24: 28-42.
- Flath, D.L. 1998. Species of special interest or concern. Montana Department of Fish, Widlife and Parks, Helena, MT. March, 1998. 7 p.
- Flath, D.L. 2002. Reptile and amphibian surveys in the Madison-Missouri River Corridor, Montana. Annual Progress Report. 14pp.
- Frair, W. 1983. Serological survey of softshells with other turtles. Journal of Herpetology 17:75-79.
- Galbraith, D. A., M. W. Chandler, and R. J. Brooks. 1987. The fine structure of home ranges of male Chelydra serpentina: are snapping turtles territorial? Canadian Journal of Zoology 65(11): 2623-2629.
- Galbraith, D.A. and R.J. Brooks. 1989. Age estimates for snapping turtles. Journal of Wildlife Management 53(2): 502-508.
- Galbraith, D.A., R.J. Brooks, and M.E. Obbard. 1989. The influence of growth rate on age and body size at maturity in female snapping turtles (Chelydra serpentina). Copeia (4): 896-904.
- Galois, P., M. Leveille, L. Bouthillier, C. Daigle, and S. Parren. 2002. Movement patterns, activity, and home range of the eastern spiny softshell turtle (Apalone spinifera) in northern Lake Champlain, Quebec, Vermont. Journal of Herpetology 36:402-411.
- Gardner, J.D., A.P. Russel, and D.B. Brinkman. 1995. Systematics and taxonomy of soft-shelled turtles (Family Trionychidae) from the Judith River Group (mid-Campanian) of North America. Canadian Journal of Earth Science. 32:631-643.
- Gettinger, R.D., G.L. Paukstis, and G.C. Packard. 1984. Influence of hydric environment on oxygen consumption by embryonic turtles Chelydra serpentina and Trionyx spiniferus. Physiological Zoology 57: 468-473.
- Graham, T.E. and A.A. Graham. 1991. Trionyx spiniferus spiniferus (eastern spiny softshell). Burying behavior. Herpetological Review 22(2): 56-57.
- Greenbaum, E. and J.L. Carr. 2001. Sexual differentiation in the spiny softshell turtle (Apalone spinifera), a species with genetic sex determination. Journal of Experimental Zoology 290(2):190-200.
- Halk, J.H. 1986b. Life history notes: Trionyx spiniferus. Herpetological Review 17(3): 65
- Hanauska-Brown, L., B.A. Maxell, A. Petersen, and S. Story. 2014. Diversity Monitoring in Montana 2008-2010 Final Report. Montana Fish, Wildlife & Parks. Helena, MT. 78 pp.
- Haxton, T. 2000. Road mortality of snapping turtles, Chelydra serpentina, in central Ontario during their nesting period. The Canadian Field Naturalist 114(1): 106.
- Hayden, F.V. 1858. Catalogue of the collections in geology and natural history, obtained by the expedition under command of Lieutenant G.K. Warren, Topographical Engineers. pp. 104-105. In: F.N. Shubert (1981) Explorer on the northern plains: Lieutenant Gouverneur K. Warren's preliminary report of explorations in Nebraska and Dakota, in the years 1855-'56-'57. Engineer Historical Studies No. 2. Office of the Chief of Engineers, Washington, DC. 125 p.
- Hayden, F.V. 1862. On the geology and natural history of the upper Missouri. Transactions of the American Philosophical Society New Series 12(1): 1-218
- Hendricks, P. and J.D. Reichel. 1998. Amphibian and reptile survey on Montana refuges: 1996. Montana Natural Heritage Program, Helena, MT. 19 p.
- Hoff, G. and D.O. Trainer. 1973. Arboviruses in reptiles:isolation of a Bunyamwera group viru, from a Naturally Infected turtle. Journal of Herpetology; 7(2) :55-62.
- Iverson, J.B. 1991. Patterns of survivorship in turtles (order Testudines). Canadian Journal of Zoology 69: 385-391.
- Joslin, Gayle, and Heidi B. Youmans. 1999. Effects of recreation on Rocky Mountain wildlife: a review for Montana. [Montana]: Montana Chapter of the Wildlife Society.
- Lewis, M., Clark, W., and Members of the Corps of Discovery. (2002). The Journals of the Lewis and Clark Expedition (G. Moulton, Ed.). Lincoln: University of Nebraska Press. Retrieved Oct. 1, 2005, from the University of Nebraska Press / University of Nebraska-Lincoln Libraries-Electronic Text Center, The Journals of the Lewis and Clark Expedition.
- Matthews, W.L. 1979. Wibaux-Beach wildlife baseline study - nongame species. Bureau of Land Management, Miles City, MT. 93 p.
- McEneaney, T. and J. Jensen. 1974. The reptiles and amphibians of the Charles M. Russell National Wildlife Range - 1974. Charles M. Russell National Wildlife Refuge. Lewistown, MT. 3 p.
- Meylan, P.A. 1982. The squamate reptiles of the Inglis IA fauna (Irvintonian: Citrus County, Florida:. Bulletin of Florida State Museum of Biological Science 27:1-85.
- Meylan, P.A. and R.G. Webb. 1988. Trionyx swinhoei (Gray) 1873, a valid species of living soft-shelled turtle (Family Trionychidae) from China. Journal of Herpetology 22.
- Moulton, G.E. editor. 1983. The Journals of the Lewis and Clark Expedition. University of Nebraska Press, Lincoln & London.
- OEA Research. 1985. Wildlife Inventory:Monitoring Report for the CX Ranch Project. 1983-1984. Unpublished report for Consolidation Coal Company, Pittsburgh, Pennsylvania.
- Oldham, M.J. 1990. Ontario herpetological summary. pp. 195-205. In: Allen, G.M., Eagles, P.F.J. & Price, S.D. [Eds]. Conserving Carolinian Canada. Conservation biology in the deciduous forest region. University of Waterloo Press, Waterloo, Ontario.
- Ostovar, K., G. Wolff, D. Dockery, U. Hoensch, M. Ruggles, A. Massey, R. Robinett, and E. Radonski. 2021. Population structure of the spiny softshell turtle (Apalone spinifera) in five Montana rivers. Chelonian Conservation and Biology 20(2):242-253.
- Packard, G.C. and M.J. Packard. 1990a. Growth of embryonic softshell turtles is unaffected by uremia. Canadian Journal of Zoology 68(5) 1990: 841-844, illustr.
- Packard, G.C., T.L. Taigen, M.J. Packard, and T.J. Boardman. 1981. Changes in mass of eggs of soft-shell turtles (Trionyx spiniferus) incubated under hydric conditions simulating those of natural nests. Journal of Zoology 193: 81-90.
- Packard, G.C., T.L. Taigen, T.J. Boardman, M.J. Tracy, and C.R. Tracy. 1979. Changes in mass of softshell turtle (Trionyx spiniferus) eggs incubated on substrates differing in water potential. Herpetologica 35: 78-86.
- Packard, M.J. and G.C. Packard. 1979. Structure of the shell and tertiary membranes of eggs of softshell turtles (Trionyx spiniferus). Journal of Morphology 159: 131-143.
- Packard, M.J. and G.C. Packard. 1991. Sources of calcium, magnesium, and phosphorus for embryonic soft-shell turtles (Trionyx spiniferus). Journal of Experimental Zoology 258(2): 151-157.
- Pettit, K. E., C. A. Bishop, and R. J. Brooks. 1995. Home range and movements of the common snapping turtle, Chelydra serpentina serpentina, in a coastal wetland of Hamilton Harbour, Lake Ontario, Canada. Canadian Field Naturalist 109(2): 192-200.
- Phillips, C.A., W.W. Dimmick, and J.L. Carr. 1996. Conservation genetics of the common snapping turtle (Chelydra serpentina). Conservation Biology 10(2): 397-405.
- Platt, S.G. and C.G. Brantley. 1991. Apalone spinifera (spiny softshell). Behavior. Herpetological Review 22: 57.
- Plummer, M.V. 1976. Some aspects of nesting success in the turtle, Trionyx muticus. Herpetologica 32: 353-359.
- Plummer, M.V. 1977b. Reproduction and growth in the turtle Trionyx muticus. Copeia 1977:440-447.
- Plummer, M.V., T.L. Crabill, N.E. Mills, and S.L. Allen. 2005. Body temperatures of free-ranging softshell turtles (Apalone spinifera) in a small stream. Herpetological Review 36(4):371-375.
- Reese, S.A., D.C. Jackson, and G.R. Ultsch. 2003. Hibernation in feshwater turtles: softshell turtles (Apalone spinifera) are the most intolerant of anoxia among North American species. Journal of Comparative Physiology B Biochemical Systemic and Environmental Physiology 173(3):263-268.
- Reichel, J. and D. Flath. 1995. Identification of Montana's amphibians and reptiles. Montana Outdoors 26(3):15-34.
- Reichel, J. D. 1996. Preliminary colonial nesting bird survey on the Bureau of Land Management Lewistown District: 1995. Unpublished report, U.S. Bureau of Land Management, Lewistown, Montana.
- Reichel, J.D. 1995a. Preliminary amphibian and reptile survey of the Lewis & Clark National Forest: 1994. Montana Natural Heritage Program. Helena, MT. 92 p.
- Reichel, J.D. 1995b. Preliminary amphibian and reptile survey of the Sioux District of the Custer National Forest: 1994. Montana Natural Heritage Program, Helena, MT. 75 p.
- Roberts, N.C. 1985. A preliminary report on the status of Chelydridae, Trioncychidae[Trionychidae], and Testidinidae[Testudinidae] in the region of Baja California, Mexico. Desert Tortoise Council Proceedings of Symposium 7: 154-161.
- Robertson, S.L. and E.N. Smith. 1982. Evaporative water loss in the spiny soft-shelled turtle Trionyx spiniferus. Physiological Zoology 55(2): 124-129.
- Roedel, M.D. and P. Hendricks. 1998a. Amphibian and reptile survey on the Bureau of Land Management Lewistown District: 1995-1998. Montana Natural Heritage Program, Helena, MT. 53 p.
- Roedel, M.D. and P. Hendricks. 1998b. Amphibian and reptile inventory on the Headwaters and Dillon Resource Areas in conjunction with Red Rocks Lakes National Wildlife Refuge: 1996-1998. Montana Natural Heritage Program, Helena, MT. 46 p.
- Seidel, M.E. 1975. Osmoregulation in the turtle Trionyx spiniferus from brackish and freshwater. Copeia 1975: 124-128.
- Shaffer, H.B., P. Meylan, and M.L. McKnight. 1997. Tests of turtle phylogeny: moecular, morphological, and paleontological approaches. Systemic Biology 46:235-268.
- Sheil, C.A. 2003. Osteology and skeletal development of Apalone spinifera (Reptilia:Testudines:Trionychidae). Journal of Morphology 256:42-78.
- Sites, J. W., Jr., and K. A. Crandall. 1997. Testing species boundaries in biodiversity studies. Conservation Biology 11:1289-1297.
- Smith, E.N., S.L. Robertson, and S.R. Adams. 1981. Thermoregulation of the spiny soft-shelled turtle Trionyx spinifer. Physiological Zoology 54(1): 74-80.
- Stone, P.A., J.L. Dobie, and R.P. Henry. 1992a. Cutaneous surface area and bimodal respiration in soft-shelled (Trionyx spiniferus), stinkpot (Stemotherus odoratus), and mud turtles (Kinostemon subrubrum). Physiological Zoology 65(2): 311-330,
- Stone, P.A., J.L. Dobie, and R.P. Henry. 1992b. The effect of aquatic oxygen levels on diving and ventilatory behavior in soft-shelled (Trionyx spiniferus), stinkpot (Sternotherus odoratus), and mud turtles (Kinosternon subrubrum). Physiological Zoology 65(2): 331-345.
- Stuart, J.N. 1988. Geographic distributin. Trionyx spiniferus emoryi (Texas spiny softshell). Herpetological Review 19(1): 22.
- Tornabene, B.J. 2014. Movements, habitats, and nesting ecology of Spiny Softshells in the Missouri River: The Influence of natural and anthropogenic factors. M.Sc. Thesis. Bozeman, MT: Montana State University. 215 p.
- Tucker, J.K. and D.A. Warner. 1998. Apalone spinifera (Spiny Softshell) reproduction. Herpetological Review 29(4): 234.
- Vitt, L.J., J.P. Caldwell, and D.B. Shepard. 2005. Inventory of amphibians and reptiles in the Billings Field Office Region, Montana. Sam Noble Oklahoma Museum of Natural History and Department of Zoology, University of Oklahoma, Norman, OK. 33 pp.
- Vose, R.L. 1964. Nesting habits of the soft shelled turtles (Trionyx species). Proceedings of the Minnesota Academy of Science 31: 122-124.
- VTN Colorado, Inc. Decker Coal Company., 1975, Draft environmental impact assessment for the proposed North Extension of the West Decker Mine.
- Walcheck, K. 1976. Montana Wildlife 170 years ago. Montana Outdoors 7(4): 15-30.
- Walker, D., P.E. Moler, K.A. Buhlmann, and J.C. Avise. 1998. Phylogeographic uniformity in mitochondrial DNA of the snapping turtle (Chelydra serpentina). Animal Conservation 1: 55-60.
- Watermolen, D.J. 2004. Softshell turtles (Apalone spp.) as bald eagle prey. Bulletin of the Chicago Herpetological Society 39(4):69-70.
- Weisrock, D.W. 1997. Molecular phylogenetics of north American softshell turtles. Unpublished M.S. Thesis, Iowa State University, Ames, IA.
- Werner, J.K., B.A. Maxell, P. Hendricks and D.L. Flath. 2004. Amphibians and Reptiles of Montana. Mountain Press Publishing Company: Missoula, MT. 262 pp.
- Wied, M.P. 1865. Verzeichniss der reptilien, welche auf einer reise in nordlichen America beobachtet wurden, von Maximilian, Prinzen zu Wied. Eigengangen bei der Akademie am 1, Juni 1865. Druck von E. Blochmann und Sohn, Dresden, Germany. 141 p.
- Wood, R.C. 1979. First record of a fossil Trionychid skull from Africa. Herpetological Review 35(4): 360-364.
- Zangerl, R. 1939. The homology of the shell elements in turtles. Journal of Morphology 65:383-406.
- Additional Sources of Information Related to "Reptiles"