orientation of the teeth varies in the jaw, with the posterior teeth being orientated backward. The palatal teeth, likely in combination with a fleshy tongue probably aided in gripping and swallowing prey. Skin Skin impressions of Champsosaurus have been reported. They consist of small (0.6-0.1 mm) pustulate and rhomboid scales, with the largest scales being located on the lateral sides of the body, decreasing in size dorsally, no osteoderms were present. Classification Champsosaurus belongs to the Neochoristodera, a clade within Choristodera, the members of which are characterised by elongated snouts and expanded temporal arches. The group first appeared during the Early Cretaceous in Asia, and are suggested to have evolved in the regional absence of aquatic crocodyliformes. While Neochoristodera is a well supported grouping, the relationships of the members of the group to each other are uncertain, with the clade having been recovered as a polytomy in recent analyses. Phylogeny of Choristodera after Dong and colleagues (2020). Paleobiology Champsosaurus is thought to have been highly specialised for aquatic life. Erickson 1985 suggested that the expanded temporal arches, which likely anchored powerful jaw muscles, and elongated snout allowed Champsosaurus to prey on fish akin to modern gharials, with these adaptions allowing rapid movement of the head and jaws for prey capture. A study in 2021 found that the middle and posteror neck vertebrae of Champsosaurus were adapted for lateral movement, and that Champsosaurus may have fed by laterally sweeping its head, using its slender jaws to grab individual fish from shoals, akin to how modern gharials feed. The mechanism of head movement is different from that of gharials, where the lateral movement occurs at the head-neck joint. It is unlikely that Champsosaurus fed by intertial feeding (where the prey is temporarily let go and the head moved forwards in order to force the prey deeper into the throat), but that the prey was moved down the throat by the tongue in combination with the palatal dentition. Erickston 1985 proposed that the position of the nostrils at the front of the snout allowed Champsosaurus to spend large amounts of time at the bottom of water bodies, with the head being angled upwards to allow the snout to act like a snorkel when the animal needed to breathe. However, later studies suggested that the neck vertebrae of Champsosaurus only had a limited ability to flex upwards. Champsosaurus co-existed with similarly sized aquatic crocodilians