Alligator Snapping Turtle

Macrochelys temminckii (Troost, in Harlan, 1835)

head of alligator snapping turtle
The head of an Alligator Snapping Turtle specimen in Louisiana. photo by C.A. Phillips
Alligator Snapping Turtle
An Alligator Snapping Turtle in Union County, Illinois. photo by C.A. Phillips

Key Characters: Wormlike lure on tongue; three prominent keels on upper shell; extra set of marginals (= supramarginals) separates true marginals 4-7 from pleural scutes.

Similar Species: Common Snapping Turtle. See Key to Adult Turtles of Illinois for help with identification.

Subspecies: None recognized

Description: Largest freshwater turtle in North America (record is 80 cm CL). Wild individuals rarely reach 70 kg (155 lb), but captives may exceed 100 kg (220 lb). Carapace sculptured, dull black or brown, and strongly serrate posteriorly. Three carapacial keels formed by pyramid-shaped elevations of vertebral and pleural scutes. Plastron reduced and cross-shaped. Head cannot be retracted within shell. Chin, throat, and neck decked with long, pointed tubercles. Tail nearly as long as shell. Male larger than female. Male cloacal opening extends about twice as far beyond back edge of shell (mean = 19.9 cm).

Habitat: Chiefly riverine, but also oxbow lakes, cypress swamps, and canals.

Natural History: Wormlike projection on floor of mouth effectively lures fish within range of jaws. Eats almost anything it can catch, including other turtles. Its eggs and young are eaten by a variety of predators including raccoons, skunks, otters, and fish. Humans are chief predator of large adults. Large female captured in Union County in late June contained 32 spherical eggs, the largest of which was 35 mm diameter. Gaping jaws and strongly hooked beak of enraged adult are efficient deterrents to most potential predators.

Distribution Notes: The status of the Alligator Snapping Turtle in Illinois has been the subject of extensive debate since the Illinois Department of Natural Resources announced plans to reintroduce the species to Illinois waters in 2005. With less than 20 confirmed records in Illinois, the species has been considered an infrequent visitor; the result of rare, long-distance migrants from the south via the large rivers. Ed Moll (1988, Unpublished report to the IL Endangered Species Protection Board) considered all records north of St. Louis questionable and considered the Big Muddy River and its confluence with the Mississippi River as the most promising area in the state to search for viable populations. The most recent record for the state is from Union County, captured and released in 2014: Kessler, E. J., C. A. Phillips, S. R. Ballard, and M. J. Dreslik. 2017.  The first record of an Alligator Snapping Turtle (Macrochelys temminckii) in Illinois in 30 years. Southeastern Naturalist. 16(3):29-35.

Status: State endangered.

Etymology: Macrochelys – macro (Greek) for long; chelys (Greek) for tortoise, turtle, water-serpent; temminckii – (New Latin) in honor of Coenraad Jacob Temminck (1778-1858).

Original Description: Troost, G. 1835. In: R. Harlan. Medical and Physica Researches or Original Memoires in Medicine, Surgery, Physiology, Geology, Zoology, and Comparative Anatomy. L.R. Bailey, Philadelphia. xxxix + 653 pp. G. Troost is usually credited with authorship of this species because the description appeared in a footnote he wrote dated 11 February 1835 that was asterisked in the Chelydra serpentina species account in Harlan (1835).

Type Specimen: Bour (1987. Type-specimen of the Alligator Snapper, Macroclemys temminckii (Harlan, 1835). Journal of Herpetology 21 (4): 340-343) and Pritchard (1989. The alligator snapping turtle: biology and conservation. Milwaukee Public Mus., Milwaukee 104 pp.) considered MNHN Laboratory of Comparative Anatomy No. A 4540 the holotype, but Hoogmoed reports RMNH 6166 as the holotype.

Type Locality: “tributary stream of the Mississippi, which enters the river above Memphis, in West Tennessee”. Restricted to the Wolf River, Shelby County, Tennessee, USA by Bour (1987. Type-specimen of the Alligator Snapper, Macroclemys temminckii (Harlan, 1835). Journal of Herpetology 21 (4): 340-343)

Original Name: Chelonura temminckii Troost,1801

Nomenclatural History: Was placed in the genus Macroclemys until Webb (1995. The date of publication of Gray’s Catalogue of Shield Reptiles. Chelonian Conservation and Biology. 1(4):322-323) established that Macrochelys has priority.  H. Garman (1892) used the name Macroclemys lacertina to refer to the Alligator Snapping Turtle in Illinois, but that is a junior synonym.