Dinosaurs were developed from archosaur reptiles; their closest living relatives are crocodiles. One modification that was the introduced with the dinosaurs was an upright stance. Amphibians and reptiles had a splayed stance and walked with an undulating pattern because their limbs were modified from fins and their gait was modified from the swimming movement of fish. Splay stanched animals cannot sustain continued locomotion because they cannot breathe while they move; their undulating movement compresses their chest cavity. Thus, they must stop every few steps and breath before continuing on their way. Dinosaurs were engineered with an upright stance similar to the upright stance of mammals. This allowed for continual locomotion.
Dinosaurs may have served various functions in the preparation the world for humans.
1. Large numbers of their large bodies may have been necessary starting ingredients for the production of petroleum. Other theories for the origin of petroleum have it coming from diatoms or abiogenetic sources
2. They provided important experimental models for the development of mammals.
3. Birds were developed directly from sauriscian dinosaurs.