FWIW, the difference (as viwed by a chemist) probably is due to surface area to volume ratio for different shapes. IIRC, an endotherm (usually) has to retain heat, that's one reason given for the eveolution of feathers (insulation theory).
An elongate form is more likely to be found in ectothermic vertebrates than in endothermic vertebrates. What energy considerations are likely responsible for this fact? Explain.
Chemists aren't likely to know much about that. This is more a question for the biology or zoology section.
