There is some disagreement about whether the dinosaurs were warm blooded or cold blooded, or in some intermediate stage. Being large poses problems for supporting structures in the body. Therefore you get an important increase in volume, and weight. A larger animal needs more massive bones. It will need to enlarge lung size, and increase digestive capacity to get the extra food to support a larger body.
Animals adapt to their environments.
Ponies are horses who have developed smaller bodies so that they can live where the pasture is sparse. The Science Series Nova has a program on the extinction of the mammoth. The last mammoths were pygmies, only three feet tall, living in an environment where there was not enough food to support their larger ancestors. A small increase in size leads to a larger increase in weight. Think about this when you are designing flying creatures.