The most plentiful species of Graptemys, the northern or common map turtle (G. geographica) is also the most widely dispersed member of this native North American genus. The common name of the genus, ‘map turtle,’ derives from the network of lines that appear on its carapace and resemble the graphic markings on a map.

Although the species’ common name ‘common’ map turtle continues to appear in print, Brian Crother and colleagues writing for the Society for the Study of Reptiles and Amphibians in 2008 renamed the species the ‘northern’ map turtle, ”because of the possibility that the word ‘common’ might be misinterpreted to imply abundance rather than to the fact that it has a broad geographic distribution” (Crother, et. al, 2008). The common name ‘northern’ is now widely accepted by the scientific community.

First formally described by the French naturalist and explorer Charles Alexandre LeSeuer (1778-1846) in 1817, the northern map turtle is a member of the Emydidae, the chelonian family of semi-aquatic or basking turtles.

The genus name Graptemys derives from the Greek word roots grapho-, meaning writing, and -emys, meaning a freshwater turtle. The species name geographica also derives from Greek word roots, geo-, meaning earth, and again -grapho, meaning writing.

There are no recognized subspecies of the northern map turtle.

Description

Described as a medium- to large-sized species, the northern map turtle has a distinctively marked carapace from which the genus derives its common name. The carapacial background is typically olive to brown with a network of yellow, orange, or tan markings that resemble waterways or highways on a topographic map.

The pigment of the carapace typically becomes darker as the turtle ages and its the comparatively bright markings tend to fade so that any remaining patterning may be visible only when the turtle’s shell is wet. Additionally, the markings may also be obscured by the growth of algae on the carapace.

The plastron of the species is usually pale yellow, and often has darker pigment at the seams of the plastral scutes. A younger individual may have additional darker markings on its plastron that tend to fade as the turtle matures. In an older individual, the plastron may be only faintly marked or uniformly yellow in color. As a hatchling/juvenile, the northern map turtle has a pronounced medial keel on its carapace that becomes somewhat flattened as the turtle matures. The carapace of the adult is comparatively broad and only moderately keeled.

There is considerable sexual dimorphism in both size and shape within G. geographica. Substantially larger than the males, the females vary from 7.5 to 10.5 inches (19 to 26.7 centimeters) in carapace length, while the males are generally 3.5 to 6.5 inches (8.9 to 16.5 centimeters) long.

In addition to being much smaller, the male northern map turtle has a more pronounced carapacial keel at maturity, a narrower head, noticeably longer front claws, and a longer, thicker tail than that of the female (Donato, 2000).

Shape differences between male and female northern map turtles include a comparatively rounded carapace in the female whereas that of the male is more oval. The head of the female is larger and broader than that of the male, enabling her to consume larger hard-shelled prey than the male.

As is typical of many turtle species, the tail of the male northern map turtle is proportionately longer and thicker than that of the female. The claws on his forefeet are longer than those of the female.

Yellow striping on the head, neck, and limbs is the single most common marking found on semi-aquatic turtles worldwide. These light stripes on a darker background provide camouflage in a wetland ecosystem with submerged aquatic vegetation, affording the striped turtle some protection from predators (Gibbons and Greene, 2009).

G. geographica hatches with the stripes on its skin and retains those markings throughout its life. The species has thin yellow, yellow-orange, yellow-green, or tan striping on an olive, brown, or black background on its head, neck, and limbs. With the abundance of aquatic vegetation in its preferred habitats, the yellow striping helps disguise the northern map turtle when it is underwater.

Range and Habitat

Endemic to North America, the upper reaches of the northern map turtle’s range are Quebec and Ontario in southern Canada. Alabama and Arkansas, Tennessee, and northern Georgia in the southern United States are the southernmost reaches of the species. The species ranges west throughout the Great Lakes to southern Wisconsin and eastern Minnesota, as well as through Kansas and northern Oklahoma. The species also inhabits the Susquehanna River system in Pennsylvania and Maryland and the Delaware River (Donato, 2000), but is rarely found in the Mississippi River (Partymiller).

The northern map turtle also inhabits river drainages in the northeastern United States that empty into the Atlantic Ocean as well as drainages in the southeastern United States that empty into the Gulf of Mexico.

Preferring aquatic biomes such as large lakes and rivers with sand- and gravel-covered substrates, the northern map turtle requires basking places such as fallen logs, snags, and rocks. Clear, flowing fresh water, plentiful underwater vegetation, copious food sources, and an abundance of hiding places are the habitat features preferred by the species (Partymiller).

Natural History

An avid but wary basking turtle, G. geographica spends much of the day during warm weather out of the water sunbathing on any suitable surface. Naturalists and hikers often observe individuals sunning themselves as well as communally basking in groups of their own species or with sympatric species (other species occurring in the same geographical area).

Diurnal in their activity patterns, meaning they are active during the daylight hours, northern map turtles spend their time during warm weather either foraging for food in morning and late afternoon or basking at midday. The species is shy by nature, and the slightest disturbance or perceived threat will cause the turtle(s) to dive into the water seeking escape and concealment.

Known as brumation, cold weather dormancy is a state of torpor in reptiles that involves reduced metabolic activity, thus conserving energy during periods of lower air temperatures and diminished daylight hours when food is comparatively scarce.

Brumation in G. geographica generally occurs from November through March depending on the ambient temperature. In the northerly reaches of its range, brumation commences earlier and lasts longer, while in the southerly portions brumation may begin later and last for a shorter period of time, depending on meteorological factors.

Spending the winter months underwater, the northern map turtle brumates on the bottom surface of the waterbody or wedged beneath submerged rocks or logs. During brumation, G. geographica does not surface to breathe air and instead absorbs oxygen from the water (Northern Map Turtle).