A softshell turtle has a flattened more hydrodynamic shell that allows it to swim much faster in the water than turtles that have a high domes shell. What type of adaptation would this be?

hmm i would say its natural selection but Turtles, like all animals, must acquire resources from their habitat, avoid predators and reproduce. Most turtles are equipped with a rigid shell that protects them from predators and plays a big role in their survival strategy. By contrast, the softshell turtles, family Trionychidae, have abandoned the protection of the hard shell, and evolved a lifestyle that compensates for this loss. Softshell turtles are very aquatic, and rarely leave the water. They prefer to live in sandy - or muddy-bottomed waters, where they will spend long periods buried in the substrate. Their long necks and snorkel-like noses allow them to access the surface to breathe. Different species and subspecies of the family show preferences for different types of bodies of water. For instance, the Florida softshell turtle (Apalone ferox) prefers quiet, still bodies of water, while the smooth softshell turtle (Apalone muticus) prefers moving waters.

Feeding Strategy

Softshell turtles are carnivorous, and consume fish, crustaceans, amphibians, insects and any other creatures small enough to be eaten. Softshell turtles are very graceful swimmers, and are quite adept at catching fish and other creatures that they actively pursue. Additionally, softshell turtles will lie in wait, and ambush prey items that venture within striking range. These turtles have an amazingly fast strike, and their beak-like mouth is exceptionally strong, so food does not often escape once captured.

Repro

Softshell turtles mature slowly: while males may be ready to breed by their fourth year, females take seven to nine years to mature. The adult turtles breed in the spring and egg deposition occurs during June and July. Females leave the water to deposit the eggs in shallow pits dug into sandy beaches. As the eggs require heat for development, beaches with full sun exposure are preferred. The eggs develop over a period of 60 to 90 days, after which the young will break out of the eggs using their temporary egg-tooth and front legs.

Winter Dormancy

Soft shell turtles hibernate from late autumn until spring. When the time comes they will bury themselves in the mud or sand at the bottom of a river or lake, and go to sleep for the winter. Though food is not necessary during this dormant period, the turtles still require oxygen, albeit at a reduced rate. To supply the remaining oxygen demand, these turtles engage in pharyngeal breathing. Pharyngeal breathing is carried out by gas-exchanging structures in the turtle's mouth and throat. This type of breathing can't keep up with the oxygen demands of an active turtle, but can supply a dormant turtle with enough oxygen to survive.

Avoiding Predators

One of the biggest challenges for soft shell turtles is that they lack a hard, protective shell. While it is true that the soft shell's shell is leathery rather than, they are still protected by an impressive rib cage. Additionally, soft shell turtles often achieve large sizes, which in itself offers protection