Final answer:
John Bell Hatcher is best known for collecting dinosaur specimens for paleontologist O.C. Marsh and did not coin the term 'heterotherm'.
Step-by-step explanation:
The answer to the question "John Bell Hatcher _________________" is A. collected dinosaurs for O.C. Marsh. John Bell Hatcher was a renowned paleontologist who worked extensively with Othniel Charles Marsh, collecting dinosaur specimens during the late 19th century, a time when the field of paleontology was rapidly developing.
He did not discover Deinodon, which was known prior to his time, nor did he work for Edward Drinker Cope, who was Marsh's rival. Additionally, the term 'heterotherm' was not coined by him.