Map turtles are a distinct group of freshwater reptiles recognized for their unique shell patterns. These aquatic turtles belong to the genus Graptemys, encompassing several species found across North America. Their common name reflects the intricate designs on their carapaces, which often resemble topographical maps or waterways.
Key Features
Map turtles have specific physical attributes. Their most prominent feature is the “map-like” pattern on their upper shell, the carapace. This pattern typically displays yellow, tan, or orange lines against an olive, brown, or black background, resembling contour lines or a network of rivers. These markings may fade as the turtle ages.
Another characteristic is a ridge, or keel, running down the center of their carapace. This keel can be pronounced, especially in younger individuals, and in some species, may have serrated scutes, leading to the alternative common name “sawbacks.”
Map turtles exhibit sexual dimorphism, with females growing considerably larger than males. Females can reach lengths of 10 to 29.5 cm, and in some species, can be twice as long and ten times heavier than males, whose lengths typically range from 7 to 16 cm.
Distinctive markings are also present on their heads, necks, and limbs, usually appearing as bold yellow or cream-colored lines and spots against a darker skin tone. The arrangement of these markings, especially on the head, varies between species and serves as an identification tool. Males often have longer front claws and a longer, thicker tail compared to females.
Where They Live and What They Do
Map turtles primarily inhabit freshwater environments across North America. They prefer large bodies of water such as rivers, lakes, and extensive ponds with slow to moderate currents. These habitats feature abundant aquatic vegetation and numerous basking sites like logs, rocks, or fallen trees. Clean water is preferred by these species.
Their diet is omnivorous, varying between sexes and species. Females, with larger heads and stronger jaws, often specialize in crushing hard-shelled prey like mollusks (snails and clams), crayfish, and aquatic insects. Males and younger turtles consume smaller mollusks, insects, and other soft-bodied invertebrates. Feeding occurs underwater.
Map turtles are diurnal. They spend much time basking in the sun on emergent structures to regulate their body temperature. These turtles are cautious and shy, often quickly retreating into the water if disturbed while basking. Their long, webbed digits and streamlined bodies make them adept swimmers, suited for navigating currents.
Exploring Different Species
The genus Graptemys includes 14 recognized species, showcasing diverse forms. While all map turtles share the genus’s defining features, individual species exhibit subtle variations in shell patterns, coloration, and head markings. These differences often relate to their geographic distributions and ecological niches.
Examples include the Common Map Turtle (Graptemys geographica), known for its widespread distribution across eastern North America, from Quebec to parts of the Great Lakes and Mississippi River drainages. The Ouachita Map Turtle (Graptemys ouachitensis) is prevalent in the Mississippi River system and its tributaries, extending into states like Minnesota, Iowa, and Texas. The Mississippi Map Turtle (Graptemys pseudogeographica kohnii) is found predominantly in the central United States along the Mississippi River and its associated waterways. Map turtle species are often restricted to specific river systems or regions within North America.