Heat exchange is proportional to surface area. That means a cube will lost or gain heat at a rate that is 24/34 or 71% as quickly as an elongated object of the same volume. That means a cube shaped endotherm and ectotherm would both lose heat more slowly to the environment. Since an endotherm generates most of its heat metabolically, a cube shape would help it conserve more of its heat, epsecially in cold climates. However, sometimes an endotherm may need to lose heat more quickly. For example Africans living in east Africa are often tall and slim, which increases body surface, but it is beneficial to them because the main problem they face is NOT retaining heat but to lose excess body heat quickly after exercising. OTOH, an eskimo living in Siberia may not benefit front the same body shape because his main problem is to retain body heat in a cold environment. Therefore, depending on the environment, sometimes an endotherm can actually benefit from an elongated body form.
The same is true of ectotherms. When the climate is cool, an elongated ectotherm can collect more heat from the environment (by basking or coming into contact with warm surfaces heated by the sun) quickly than a cube-shaped one. However, at night, the same elongated ectotherm will lose heat more quickly to the environment than the cube-shaped one as well. If the climate is warm, then a cube shaped ectotherm has the advantage, since it can retain more of the body heat when the sun goes down. By retaining more heat, it does not have to bask as long or not at all the next morning. As experienced lizard catchers know, the early morning is the best time to catch them, because their body temperature has fallen overnight and the sun is not up long enough for them to fully warm up, making them sluggish and easy to catch. OTOH, if an ectotherm has less body surface, then it can retain more heat overnight and it can be active earlier and would not be so defenseless as it tries to warm up. Another way to reduce surface to volume ratio, besides being cube-shaped, is to evolve large body size. That is exactly what the dinosaurs did during the Mesozoic. They evolved large body size to take advantage of the warm Mesozoic climate. A large dinosaur can theoretically remain active during the night or they can at least become active earlier in the morning and not be in danger of being eaten during the early morning because they lost too much heat overnight and are sluggish. However, if the climate is cool, large dinosaurs are once again at a disadvantage, because it will take them a long time to warm up in a cool climate because of the small amount of body surface. Therefore it depends on the climate as to whether being elongated or being large is a disadvantage or an advantage, whether one is endothermic or ectothermic.
