Endothermy in champsosaurs?
As previously explored, champsosaurs were fully aquatic reptiles, living in areas with ostensibly cold temperatures. Champsosaurus itself was found in Axel Heiberg and Greenland, two areas that, while much warmer when it was alive, were still subjected to long polar nights. It’s Palaeocene range across North America also had a recognisable temperate climate, to the point that the only crocodyllians co-existing with these animals were cold-tolerant alligatoroids.
Likewise, most modern endothermic aquatic sauropsids engage in basking behaviour. Champsosaurs appareantly could not do this; the only known neochoristoderes that could move on land were the females of Champsosaurus laramiensis/ambulator (they are considered synonimous, btw), thus ruling out basking behaviour from most known taxa.
The torso is also noted as being very rotund for the standards of Choristodera, meaning that it probably evolved as means to cope with heat conservation.