Land bridges were everywhere during the extinction, many species were spreading, and there were many diseases.

Theories

In his 1986 work The Dinosaur Heresies Bakker puts forth the theory that dinosaurs were warm-blooded his evidence for which includes:
Almost all animals that walk upright today are warm-blooded and dinosaurs walked upright. He attributes his interest in dinosaurs to his reading an article in the September 7 1953 issue of Life magazine. Along with his mentor John Ostrom Bakker was responsible for initiating the ongoing "dinosaur renaissance" in paleontological studies beginning with Bakker's article "Dinosaur Renaissance" Scientific American April 1975 .

He revealed the first evidence of parental care at nesting sites for Allosaurus. Along with his mentor John Ostrom Bakker was responsible for initiating the ongoing "dinosaur renaissance" in paleontological studies beginning with Bakker's article "Dinosaur Renaissance" Scientific American April 1975 . His seminal work The Dinosaur Heresies was publiRobert T. Bakkerd in 1986.