Presumably male and female
They are a dull brown color. One of the sailbacks is considerably smaller than their partner and has a smaller sail. This may be the sexual dimorphism of Spinosaurus in The Land Before Time.
After Swooper, Petrie, and Guido leave Black Rock, Swooper eventually gets tired and asks if it is safe for him to land and rest. Upon looking down from Swooper's back, Petrie and Guido see the Sailback Sharpteeth and her mate standing on the ground and looking hungrily up at them. Petrie and Guido wisely tell Swooper to keep on flying.