Why can't mammals grow as large as the largest dinosaurs?

Now, as for land-dwelling mammals: To start with, while the measurable difference in size between the largest mammal and the largest dinosaur is many-fold, the effective difference is not that large, especially in terms of body length. read more

Mammals have grown as large or larger than just about all but the largest dinosaurs. The paraceratherium, an extinct type of rhinoceros was 27 feet tall and 40 feet long. The giant ground sloth, megatherium was 20 eat long and weighed 4 tons. read more

The extinction of the dinosaurs, 65 million years ago, allowed mammals to rapidly evolve a range of body sizes, according to a November 2010 study. But even so, no land-dwelling mammals were able to get as large as the largest dinosaurs. Biologist Felisa Smith, an author of the study, explained. Felisa Smith: Mammals are what are called endotherms. read more

One reason that often gets overlooked is dinosaurian respiratory systems. This is the reason why the largest of mammals (the 8 meter-long Paraceratherium comes to mind) were nowhere near to approaching the largest dinosaurs (sauropods such as the 26 meter Dreadnoughtus) in size. Mammals have a bidirectional respiratory system. read more