>> Understanding the real sizes of different dinosaurs is a lot trickier,
because we don't have the living animals to measure or
weight and the fossilized skeletons really only include the bones.
These skeletons are usually incomplete as well.
And we can make estimates about the length and
the height based on those incomplete or nearly-complete skeletons.
But, understanding how heavy the dinosaur was is a lot trickier.
Because, the bones have been infilled by minerals so they're too heavy.
And, we do not have all of the skin, muscles, and organs of that dinosaur.
Additionally, dinosaurs, like birds,
often had extensive air sac systems throughout their bodies.
And that means that dinosaurs,
like birds, had a lot more air inside those bodies than mammals do.
And that makes it difficult to equate the body weight of
an elephant-sized dinosaur with an elephant, for example.