Why were dinosaurs so big?

and why are there no dinosaur-sized (land) mammals? and why were the first dinosaurs bipedal? and why were so many dinosaurs bipedal? and why were dinosaurs so lightly built? and why were dinosaurs among the first flying vertebrates? and why did dinosaurs suppress mammals? and why did dinosaurs become extinct?

Interested?
http://www.microlnx.com/dinosaurs/

Actually, the largest land mammals were about the same size as the largest members of most dinosaur groups

If they aren't extinct, then why aren't they making movies about killer bipedal mammals?

Because now mammals are in charge. Living Dinosaurs (birds) are 'just part of the scenery', when speaking in terms of the modern evolutionary dynasty of mammals

Birds are not exactly well-renowned for their cinematic skills.

No that's not the reason, since dinosaurs never were *in charge* of anything.

But they are entremely well known for their acting and mimicry skills.

They ARE making movies about killer bipedal mammals. If fact, nearly EVERY movie is about killer bipedal mammals.

I think you know very well what I meant.

Excellent point!

[EL] Very informative. Thank you. EL