The liver was connected by muscle to a pelvic bone, Geist said, suggesting the animal had a breathing system called a hepatic piston. In such a system, muscles pull against the liver, causing the breathing cavity to expand slightly. That forces air into the lungs at a high rate. These theropods were exceedingly fast and dangerous animals. They were not slow and sluggish like many modern reptiles.
Mammals have a diaphragm muscle that causes the lung cavity to expand and draw in air.
The ability to rapidly ventilate the lungs is essential for moving swiftly for long periods. Dinosaurs' lung capacity may be one reason they dominated mammals for about 150 million years, said Geist. Mammals during this period were small and no match for the meat-eating dinosaur. This was like a turbocharged lizard. The mammals couldn't get a foothold and just tried to stay out of the way.