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Anatomy and morphology

C. serpentina has a rugged, muscular build with a ridged carapace (upper shell) that varies in color from tan, brown, and black, although ridges tend to be more pronounced in younger individuals. The carapace length in adulthood may be nearly 50 cm (20 in), though 25–47 cm (9.8–18.5 in) is more common. C. serpentina usually weighs 4.5–16 kg (9.9–35.3 lb). Per one study, breeding common snapping turtles were found to average 28.5 cm (11.2 in) in carapace length, 22.5 cm (8.9 in) in plastron length and weigh about 6 kg (13 lb).

Males are larger than females, with almost all weighing in excess of 10 kg (22 lb) being male and quite old, as the species continues to grow throughout life. Any specimen above the aforementioned weights is exceptional, but the heaviest wild specimen caught reportedly weighed 34 kg (75 lb). Snapping turtles kept in captivity can be quite overweight due to overfeeding and have weighed as much as 39 kg (86 lb). In the northern part of its range, the common snapping turtle is often the heaviest native freshwater turtle.

According to a study by Nakamuta et al. (2016), common snapping turtles have well-developed olfactory organs, nerves, and bulbs that suggest that this species has a great sense of smell.