Spiny Softshell - Apalone spinifera
The shell of the Spiny Softshell is flattened (pancake-like), with flexible edges and covered with leathery skin; small conical tubercles or "spines" are present on the front edge of the carapace above the neck. The snout is tubular, with a ridge along the inner margin of each nostril, which allows this turtle to remain beneath the surface with just the snout exposed. In mature males, the carapace is like 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 not notably like sandpaper, is more generally mottled or marked with blotches, the tubercles at the front edge of the carapace are more prominent than in males, and the tail is relatively short. Juveniles have characteristics that are female-like, except the carapace coloration, which is male-like. In hatchlings, the carapace is olive to tan, with small dark circles, spots, or dashes, and a yellowish margin bordered by a black line. The eggs are hard and white, smooth, thick-shelled, and about 24 to 32 millimeters in diameter. Adult females can reach 52 centimeters in carapace length, but much less in adult males (which average about 10 centimeters shorter); hatchlings are about 3 to 4 centimeters in carapace length.
The Spiny Softshell differs from other Montana turtles by having a flattened and leathery shell that is soft and lacks horny plates, and a pointed snout with tubular nostrils. The Smooth Softshell (A. muticus), which occurs in the Missouri River in southern North Dakota, differs 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.
Western Hemisphere Range
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 specific information is available for Montana. In Vermont, Spiny Softshells migrated about 3 kilometers between riverine wintering sites and river mouth nesting sites near Lake Champlain; migratory movements were most extensive in spring and late summer (Graham and Graham 1997). Annual home range size in Arkansas was 784 to 2,310 meters of stream length for males and 683 to 2,145 meters for females (Hammerson 1999).
Habitat use by Spiny Softshells in Montana is probably similar to elsewhere in the range, but studies are lacking and there is little qualitative information available. They occupy larger rivers and tributaries. Both sexes have been observed basking together on partially submerged logs in backwater sites of slow-moving water, and on sandy or muddy riverbanks.
Generally, the Spiny Softshell is primarily a riverine species, occupying large rivers and river impoundments, but also occurs in lakes, ponds along rivers, pools along intermittent streams, bayous, irrigation canals, and oxbows. It usually is found in areas with open sandy or mud banks, a soft bottom, and submerged brush and other debris. Spiny Softshells bask on shores or on partially submerged logs. They burrow into the bottoms of permanent water bodies, either shallow or relatively deep (0.5 to 7.0 meters), where they spend winter. 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).
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
The food habits in Montana have not been studied.
Generally, Spiny Softshells forage in the water, often in shallows with vegetation. They are considered to be generalist carnivores, and usually feed on the bottom. Major foods are crayfish, aquatic insects (of at least seven orders), and fishes, but mollusks, worms, isopods, amphibians, carrion, and vegetation also are eaten (Ernst et al. 1994, Hammerson 1999). The diet in an Iowa study 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 the stomachs sampled; this breakdown of categories appears representative for other states (Ernst et al. 1994). Prey may be chased, ambushed, or flushed and pursued.
Animals are active from April to October (usually May to September) in Kentucky and Colorado (Ernst et al. 1994, Hammerson 1999). Water temperatures of 12 degrees C. appear to determine when animals enter or emerge from hibernation in Vermont (Graham and Graham 1997). Adults emerge earlier from hibernation, and remain active longer into the fall, than juveniles. The period of activity in Montana is poorly documented, with records from early June to late July (Hendricks and Reichel 1996, Hendricks 1999). Egg predators include Striped and Spotted Skunks, Raccoon, Red Foxes, and probably Coyotes; young Spiny Softshells are captured and eaten by predatory fish, wading birds, and Muskrats (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.
Males reach maturity at about 8-9 cm plastron (belly shell) length, females at 18-20 cm. Mating occurs in April or May, and nesting may begin in late May and extend into August, but usually occurs in June and July in Colorado. Eggs are laid in one or more clutches in flask-shaped ground nests excavated in course sand or fine gravel to depths of 10-25 cm deep; Colorado nests contained 15-39 eggs, some clutches elsewhere contained as few as 4 eggs. Eggs hatch in about 60-80 days; hatching occurs in August to September in Colorado. Some hatchlings may overwinter in the nest and emerge the following spring (Ernst et al. 1994; Hammerson 1999). Individuals may live up to 50 years (based on rates of growth and observed carapace size), with ten-year old females having a carapace length of about 25 cm, and carapace length of ten-year old males about 16 cm; the oldest female on record (a captive zoo animal) lived 25 years.
Montana populations of the Spiny Softshell are poorly understood, making management of them more difficult. It is apparent that the construction of dams and large reservoirs on rivers (e.g. Fort Peck Dam and Reservoir) is detrimental to population continuity, effectively creating smaller isolated populations. Impacts of other habitat disturbances are not clear. Studies of nesting success, population structure, dispersal, and population size need to be conducted throughout the range of both Montana sub-populations (Missouri River and Yellowstone River). Routine surveys for Spiny Softshells in appropriate habitats could be made a standard part of the field duties of agency fishery biologists. Records should be maintained of the incidental "take" by anglers, who should be encouraged to report any captured Spiny Softshell; killed animals should be examined by agency fishery or wildlife biologists if possible so that data on sex, size, and food habits can be gathered and a base of information on the biology of this species developed. Nesting sites need to be identified and protected from disturbance by human activities.
- Literature Cited AboveLegend: View Online Publication
- Baxter, G.T. and M.D. Stone. 1985. Amphibians and reptiles of Wyoming. Second edition. Wyoming Game and Fish Department. Cheyenne, WY. 137 p.
- 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.
- 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. 1999. 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.
- Stebbins, R. C. 2003. A field guide to western reptiles and amphibians. 3rd Edition. Houghton Mifflin Company, Boston and New York. 533 p.
- 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.
- 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.
- 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. 1955. Observations on the life history of the soft-shelled turtle Trionyx ferox, with especial reference to growth. Copeia 1955:5-9.
- 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.
- Capron, M. 1987. Selected observations on south-central Kansas turtles. Kansas Herpetological Society Newsletter 67:13-15.
- Carlson, J. (Coordinator, Montana Animal Species of Concern Committee). 2003. Montana Animal Species of Concern. 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.
- 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.
- 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.
- 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.
- 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. 1862. On the geology and natural history of the upper Missouri. Transactions of the American Philosophical Society New Series 12(1): 1-218
- 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.
- Hendricks, P. and J.D. Reichel. 1998. Amphibian and reptile survey on Montana refuges: 1996. Montana Natural Heritage Program, Helena, MT. 19 p.
- Hoberg, T., and C. Gause. 1989. Reptiles & amphibians of North Dakota. North Dakota Outdoors 55(1):7-18.
- 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.
- 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.
- 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.
- 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. 1987. The phylogenetic relationships of soft-shelled turtles (family Trionychidae). Bulletin of the American Museum of Natural History 186(1): 1-101.
- 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.
- Miller, K., G.C. Packard, and M.J. Packard. 1989a. Life history notes: Trionyx spiniferus. Herpetological Review 20(2): 56.
- Miller, K., G.F. Birchard, M.J. Packard, and G.C. Packard. 1989. Trionyx spiniferus (spiny softshell turtle). Fecundity. Herpetological Review 20(2): 56.
- 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.
- 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., 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. 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., 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.
- 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.
- 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.
- Roedel, M.D. and P. Hendricks. 1998. 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.
- Vogt, R.C. and J.J. Bull. 1982a. Genetic sex determination in the spiny softshell Trionyx spiniferus (Testudines: Trionychidae)? Copeia 1982: 699-700.
- 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.
- 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. 1997. Molecular phylogenetics of north American softshell turtles. Unpublished M.S. Thesis, Iowa State University, Ames, IA.
- 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.
- 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.
- 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.
- 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"