Northern Map Turtle

Overview:

Scientific Name: Graptemys geographica
Size: 3.9 – 10.7” (adult carapace length)
Status: Locally common throughout much of the lower Great Lakes basin, but have become extirpated from more heavily polluted urban rivers.
Northern Map Turtle

Habitat:

Larger lakes, rivers, reservoirs, oxbow sloughs, and open marshes, including some bays and inlets of the Great Lakes.

Adult Coloration:

Narrow, dark-bordered yellowish to orange lines form a network on the olive or grayish brown carapace. May become obscured by dark pigment with age. Plastron yellow, sometimes with dark markings along scute borders in juveniles and males. Head, neck, and limbs dark olive, brown, or black, with many thin yellow, green, or orangish stripes. Usually with small oval or triangular light spot behind each eye.

Adult Characteristics:

Carapace fairly broad, with low to moderate keel along midline, and flared hind margin that is serrated by projecting rear edges of marginal scutes. Plastron broad and flat. Females grow larger than males (6.7 – 10.7” vs. 3.9 – 6.3” carapace length). Males have a more oval carapace with a distinct central keel, narrower head, longer front claws, and a longer thicker tail.

Juvenile Characteristics:

Rounded gray or grayish-brown carapace about 1.1” long, with light circular markings and distinct central keel. Plastron light yellow or off-white with dark borders on scutes. Striped pattern on head and limbs as in adult.

Species Confused With:

Wood Turtle lacks yellow striping on head and has a sculptured-looking carapace. Painted turtles have smooth, unserrated and unkeeled carapace with red markings under marginal scutes. Red-eared sliders have a broad reddish or orange stripe behind the eye and large black spots on the plastron (except for in some older males).

References:

Amphibians and Reptiles of the Great Lakes Region by Jim Harding
Harding, J.H. and J.A. Holman. 1990. Michigan Turtles and Lizards. MSU Cooperative Extension Service and MSU Museum. 96 pp.
Ruthven, A. G., H. B. T. Gaige, et al. 1912. The herpetology of Michigan, by Alexander B. Ruthven. Crystal Thompson and Helen Thompson; Memoranda towards a bibliography of the archaeology of Michigan, by Harlan I. Smith; prepared under the direction of Alexander G. Ruthven. Lansing, Mich., Wynkoop Hallenbeck Crawford, State Printers.
Holman, J. A. 2012. The Amphibians and Reptiles of Michigan: A Quaternary and Recent Faunal Adventure. Detroit, Mich., Wayne State University Press.
Conant, R., and Collins, J. T. 1998. Reptiles and Amphibians: Eastern, Central North America. Houghton Mifflin Harcourt Press.

Credits:

Jim Harding