Macrochelys temminckii

This is a very large turtle with a huge head, strongly hooked jaws, an extra row of scutes along each side of the shell (between the costals and marginals), three keels along the carapace, and a long tail; adult carapace length usually 38-66 cm (to 80 cm), mass 16-68 kg (to 143 kg); young are brown, with a very rough shell and long tail, 3-4.4 cm at hatching (Conant and Collins 1991). See also Lovich (1993).

This species differs from the snapping turtle in its larger head, extra row of scutes along the sides of the shell, lack of a saw-toothed middorsal tail ridge, more lateral position of the eyes, and presence of a wormlike lure on the upper surface of the tongue.

Habitat consists of slow-moving, deep water of rivers, sloughs, oxbows, and canals or lakes associated with rivers (e.g., large impoundments including reservoirs) (Ernst et al. 1994); also swamps, bayous, and ponds near rivers, and shallow creeks that are tributary to occupied rivers, sometimes including swift upland streams (Phelps 2004). This turtle sometimes enters brackish waters near river mouths. Usually it occurs in water with a mud bottom and some aquatic vegetation but uses sand-bottomed river and creeks in Florida (P. Moler, pers. comm., 2020). Within streams, alligator snapping turtles may occur under or in logjams, beneath undercut banks, under rock shelters, or in deep holes (Jensen et al. 2008). These turtles are highly aquatic and rarely are found out of water (except during nesting). In Tennessee, F. Scott (pers. comm., 1992) most often found radio-tagged turtles in less than 3 meters of water. In northeast Louisiana, Sloan and Taylor (1987) found that native turtles preferred flotant (dense floating vegetation mat) with cypress or buttonbush habitat. The turtles frequently used openings in the flotant beneath cypress trees. In the same region, Harrel et al. (1996) documented a preference for bald cypress forest by subadults; most occupied sites were associated with logs. In Missouri, higher abundance was associated with submerged physical structures, deeper water, higher levels of detritus, and warmer water (Lescher et al. 2013).

Ewert (1976) provided a description of nesting habitat. He observed 16 nests from the Apalachicola River, Florida, and one from Lake Iamonia which adjoins the Ochlockonee River, Florida. The turtles chose a variety of situations for nesting, from sand mounds along the river banks to sandbars within the stream, to a 1.5 m high steep cut bank. Conditions at the Apalachicola sites included xeric exposed sites (three nests), more mesic sites with trees nearby but open above (three nests), partially shaded sites (4 nests), and deeply shaded sites (six nests, one well within a three to five m cane stand with a completely closed canopy). Ewert suggested that many of the turtles emerged from quiet backwaters of the flooded forest, rather than the river proper. The Apalachicola nests' distance from the nearest water averaged 12 m. The one nest on an island in Lake Iamonia was in the open and was 72 m from the nearest water. Ewert and Jackson (1994) expanded this data set but not greatly altered these proportions. Jackson and Jensen (2003) reported nest sites that were about 30 and 70 m from streams.

Alligator snapping turtles are highly aquatic, emerging from water only for nesting or, uncommonly, basking (Carr et al. 2011). The turtle is secretive, a trait making it difficult to observe, and particularly difficult to find where it is also rare.

The principal predators of adults have historically been humans. Nest predation likely takes a heavy toll, and raccoons are a major factor (Sanspree et al 2016). Raccoons and river otters were the major source of mortality of released immature turtles in a study in Illinois, Oklahoma, and Louisiana (Dreslik et al. 2017). American alligators are also documented to feed on juveniles (Sanspree et al. 2016).

Mating takes place from February to April in Florida, followed by nesting from late April through mid-May along the Apalachicola River (Pritchard 1978; Ewert and Jackson 1994, Ewert et al. 2006). Oviposition apparently occurs from April through early May in Manchac, Louisiana, and from mid-May through early June near Jonesville, Louisiana (Dobie 1971). Nesting was observed in June in Butler County, Missouri (Figg 1991). Eggs number from 9 to 61 (average around 25-35) per nest, the number being related to the size of the female. In Florida, females laid 17-52 eggs (Ewert et al. 2006). Females produce only one clutch per year, and sometimes skip a year between clutches (Pritchard 1992, Ewert et al. 2006). Eggs hatch in 15-18 weeks (Ewert et al. 2006). Hatching extends throughout August in northwestern Florida, where hatching success in protected nests was 66-78% over two years (Ewert and Jackson 1994). Sex of hatchlings is influenced by incubation temperature (Ewert et al. 2006). Maturity is reached at 11 to 13 years at the earliest (Dobie 1971, Pritchard 1978). The older, larger turtles may be disproportionately important in population maintenance. Minimum temperature (especially in the northern portion of the range) and precipitation can have a large impact on nesting success (Thompson et al. 2017).

Adults may live many years. One female found in Kansas was aged (by counting annuli on scutes) at 45 years (Shipman et al 1991). Captives have lived more than 70 years (Trauth et al. 2004). Generation time is estimated to be 31.2 years (Folt et al. 2016).