Sauropod and elephant. Internal Constancy vs. Variability of Temp. Resting metabolic rate greater in mammals and birds than in reptiles. Size confers some thermal intertia. Surface area is where heat is lost.
Surface area increases as the square of linear dimension.
But volume increases as the cube. Therefore for things of similar shape, large things lose heat slower. Big animals have great thermal inertia. So big dinos could have been inertial homeotherms. Also this means that large things with high metabolic rates need to dump heat.