📝Square-cube law
Surface-area-to-volume ration decreases in larger organisms.
Larger cells have less surface area to capture resources from, compared to increased volume. That’s why larger cells are aerobic (Oxygen makes ATP synthase more effective, thus providing more energy).
Because small animals have higher surface-area-to-volume ratio, they have relatively more surface area for heat dissipation. That’s why they usually have higher metabolism rates, higher heart rates. (Mouses have 310-840 bpm heart rate) On the other hand, larger animals have very big volume and too low surface area to dissipate heat. That’s why they need very low metabolic rates. (Elephants have 30 bpm heart rate)
Combined with The Heartbeat Hypothesis, that explains why larger animals live longer.
Larger creatures need stronger bones (than would be proportionally needed)