Black-knobbed Map Turtle
Southeastern US. Limited in its range to the Mobile Bay drainages of Alabama and Mississippi.
Prefers sand and clay-bottomed streams with moderate currents and abundant basking sites of brush, logs and debris. This species is found in deeper waters more often than other species.
The black knobbed map turtle is considered a small to medium size turtle. It has broad, rounded large black knobs projecting up from the keel. The keel runs the length of the center of the carapace. The carapace is dark olive in color. The skin is light gray to dark, with yellowish pattern. The underside of the shell (plastron) has a pattern of a few horizontal lines that cover less than a third of the surface. Its feet have webbing between toes.
This is an aquatic, freshwater basking turtle and may be seen doing so during any month of the year. However, it is not active at water temperatures under 50 degrees Fahrenheit. Individual turtles return to the same site day after day. It prefers to bask on stationary logs or on tangles of logs separated from the shoreline by an area of open water.
When there are periods of high water and their preferred basking sites are submerged, they will bask on the river bank. While juveniles bask on branches near shore, adults prefer basking sites surrounded by open water. This species spends the night sleeping on brush piles and logs. They seldom leave the water except to bask or lay eggs.
Nesting season begins in late May and ends in early August. Females usually lay two or more clutches per year of 3-7 eggs. The eggs are elongated and flexible. Of the nests are constructed, 83 percent are dug in fine quartz sand with no organic matter.
The nest is dug by “bulldozing” sand with the shell and digging with sweeping motions of the front limbs. Incubation last between 60-68 days. Hatchlings remain within the nest for 8-13 days until yolk sac is absorbed. They will usually emerge from the sandy nest about one hour after dark.
• The members of the family Emydidae are commonly called "pond turtles."
• In the 1970’s map turtles were bred and hatched by the thousands for the pet trade. Then, finally, the “4 inch law” was established stating that people could not own turtles less than four inches in size and the map turtles decreased in popularity.
• The map turtle is also known as the "sawback turtle" due to the presence of a ridge that runs down the middle part of its upper shell. Most female map turtles are larger than the males, but the male map turtles have thicker tails that are typically longer than those of the females.
Habitat destruction is their greatest threat. The current IUNC Red List Status of G. nigrinoda is Near Threatened, but a revised status of Least Concern is recommended in light of recent surveys in which G. nigrinoda was the most commonly observed and collected species of emydid within its range.