Dr. Chris Carbone and colleagues from the Institute of Zoology, Zoological Society of London reason on energy grounds that mammalian top carnivores aren’t likely to be any bigger than a one ton bear.
The authors provide a model of carnivore energetics in relation to predator and prey size, and compare the model predictions with observed estimates of metabolic rates and intake rates taken from animals in the wild. By analyzing the balance between energy intake and expenditure across a range of species, the authors reveal that mammalian carnivores would not be able to exceed a body mass of one ton.
PLoS Biology 5(2): e22 – The Costs of Carnivory (Hideous word!)
They suspect that Giganotosaurus and Tyrannosaurus had a comparable total metabolic power of the largest ever mammals but a correspondingly lower metabolic rate. Maybe they were cold-blooded after all.
The sperm whale can weigh up to 45 tonnes but they aren’t included.