The Alligator Snapping Turtle (Macrochelys temminckii) is the largest freshwater turtle in North America, capturing attention due to its sheer size. This prehistoric-looking reptile, with its spiked shell and powerful jaws, spends most of its life submerged in the deep, slow-moving waters of the southeastern United States. Its impressive dimensions are a direct result of its biology and long lifespan. To appreciate the scale of this creature, it is helpful to distinguish between the typical adult size and the extraordinary measurements of rare record holders.
The Record Holders Maximum Size
The largest documented Alligator Snapping Turtles represent the peak of the species’ potential size. The largest reliably recorded specimen weighed 113.9 kilograms (251 pounds) and had a carapace length of 800 millimeters (31.5 inches). This massive turtle demonstrates the upper limit of growth achievable under ideal conditions.
Unconfirmed historical accounts, such as one from 1937, claimed a turtle weighing 183 kilograms (403 pounds), but these measurements lack scientific verification for an official record. These extraordinary sizes are achieved only by very old males who have spent decades accumulating mass. Such record-holding individuals are outliers, standing far above the typical range of the species.
Typical Adult Dimensions and Weight
For the average adult, the Alligator Snapping Turtle is still substantial, making it a true giant of its habitat. Most adults range in carapace length from 35 to 80.8 centimeters (13.8 to 31.8 inches). Their weight falls between 8.4 and 80 kilograms (19 to 176 pounds).
Size measurements are taken as the straight carapace length—the shell’s length from front to back, excluding the head or tail. Sexual dimorphism is a significant factor, as males are notably larger and heavier than females, often weighing between 70 and 90 kilograms (155 and 175 pounds). Adult females are smaller, usually topping out at the lower end of the average size range, reaching about 22 inches in length and 62 pounds in weight.
The Slow Growth Trajectory
The great size of the Alligator Snapping Turtle results from an extremely slow and continuous growth pattern tied to a long lifespan. Hatchlings are very small, measuring about 1.5 inches in carapace length upon emerging from the nest. The turtles grow slowly throughout their lives, taking many years to reach substantial size.
It takes a considerable amount of time for the turtles to reach reproductive capability, often between 11 and 21 years of age. At maturity, the straight carapace length is around 33 centimeters (13 inches) and the turtle weighs about 8 kilograms (18 pounds). Growth continues throughout the turtle’s entire life, albeit at a reduced pace, even after maturity is reached. This slow, sustained growth allows the species to achieve its remarkable dimensions, with some individuals estimated to live as long as 70 to 120 years.
Environmental Factors Influencing Size
The ultimate size an individual Alligator Snapping Turtle reaches is heavily influenced by the quality of its environment. Abundant food availability, such as fish, mollusks, and aquatic animals, directly supports faster growth and greater final mass. Turtles with access to high-quality prey are more likely to reach the upper end of the species’ size potential.
Habitat quality also plays a role. The turtles prefer deeper water in large rivers, lakes, and swamps with ample submerged structure, such as logs and root masses. These structures provide cover and are associated with higher prey densities, supporting efficient feeding. Geographic location and climate also affect size; warmer water can lead to slightly faster initial growth rates in younger turtles, though this effect is less pronounced in mature adults.