Regardless of the method used to calculate it, sauropods were indeed large. not all groups of animals become large however. this is generally thought to be because of some negative selective pressures against body size. why might large body size not always be advantageous?
a. larger animals have shorter lifespans and so are more susceptible to extinction
b. larger animals tend to be less successful at mating as they are outcompeted by their smaller counterparts.
c. larger animals have a decreased demand for resources and so can expend ess energy
d. larger animals have trouble maintaining their body temperature due to thermal inertia
e. larger animals have lower fecundity rates and so produce fewer offspring