It is known from a single species, Gunakadeit joseeae, which is based on an articulated and mostly complete skeleton from the late Triassic (middle Norian) Hound Island Volcanics of Alaska.

Gunakadeit possessed a variety of features from the two major suborders of thalattosaurs, Askeptosauroidea and Thalattosauroidea, and it is considered the most basal member of the latter group.

Gunakadeit's basal position and relatively recent occurrence implies a 20-million-year ghost lineage connecting it to the rest of Thalattosauria.

On May 18, 2011, Jim Baichtal discovered a fossil poking out of the rock and he sent a picture to professional palaeontologist Patrick Druckenmiller.

The 28 dorsal vertebrae have tall neural spines, which become pointed and bent backwards closer to the hip.

[1] The interclavicle had uniquely extensive lateral processes (side branches), which connected to very long and robust clavicles.

[1] The posterodorsal process (upper rear branch) of the ilium tapers to a point, a shape otherwise unknown in thalattosaurs.

A bone tentatively identified as the pubis is large, wide, and lacks an obturator foramen (a hole present in other thalattosaur hips).

[1] A phylogenetic analysis found Gunakadeit to be the most basal member of Thalattosauroidea, a suborder of the marine reptile order Thalattosauria.

However, it also retained several askeptosauroid-like features of the skull such as a low coronoid process and a straight, pointed jaw without much variation in tooth shape.