Range: Alabama - The Black-Knobbed Map Turtle (Cagle, 1954) is found in the Alabama, Tallapoosa, Coosa, Cahaba, Tombigbee and Black Warrior Rivers. It is also found in the streams, creeks, and lakes connected or proximal to these rivers. Mississippi - In this state it is restricted to the Tombigbee River.
Description: This is a small to medium size turtle. Males are about 3.5 to 4.5 inches as adults and females are about 6 to 8 inches long. This turtle is part of the narrow head group of map turtles and therefore is mostly an insect eater, but they are also opportunistic so crustaceans and fish could also be eaten. It has the typical map turtle central keel that is exaggerated as a hatchling and slowly wears down with age, especially old females. However, of all the map turtle species, this group (the sawback group, G. nigrinoda, G. oculifera and G. flavimaculata) has the highest central keel. This turtles differs from G. n. delticola (Delta Map Turtle) in having light gray skin as opposed to black. In G. n. nigrinoda, the plastral pattern consists of a few horizontal lines that occupies no more than a third of the plastral surface. This is unlike G. n. delticola, which has a pattern that occupies more than half of the total surface area of the plastron.
Habitat: It is associated with brush piles (trees that have died and fell into the river). It spends much of the day basking on these fallen trees and quickly jumps into the water when approached. They seek refuge on the bottom of the river and in between the branches of the falling trees. I have found that females prefer to bask further off shore and on tree stumps, in general. Males also bask in deeper water but not at the ratio that females are seen. G. nigrinoda is found in deeper water than the other two sawback species.
Legal Status Endangered in Mississippi, Protected in Alabama
Other Information: In the parts of the rivers where I have looked for G. n. nigrinoda, it was not uncommon. In some parts of these rivers, Pseudemys concinna, appears to be as common. Other species that are found in the same places as this species are Graptemys pulchra (Alabama Map), Pseudemys concinna (River Cooters), Trachemys scripta scripta x elegans (Yellowbelly x Red Eared Slider), Sternotherus minor peltifer (Stripeneck Musk), Sternotherus depressus (Flattened Musk), Macroclemys temminckii (Alligator Snapping Turtles, not Loggerheads as named by the locals), and Apalone spinifera aspera, (Gulf Coast Spiny Softshell). As mentioned previously, G. nigrinoda nigrinoda is part of the narrow head group. G. pulchra, a broad head species, can be found along side G. n. nigrinoda. I have found that in a three mile section of river, G. pulchra or G. n. nigrinoda can be the dominate basking turtle in a certain area. While going up river in this three mile section, the most dominate Graptemys species changed three times.
Previous Taxonomy: Graptemys oculifera nigrinoda Cagle, 1954
The dorsal view a G. n. nigrinoda and a G. n. delticola.