The Doctor and the Dinosaurs — Mike Resnick

Welcome to a Steampunk wild west starring Doc Holliday, with zombies, dinosaurs, robots, and cowboys.

The time is April, 1885. Doc Holliday lies in bed in a sanitarium in Leadville, Colorado, expecting never to leave his room again. But the medicine man and great chief Geronimo needs him for one last adventure. Renegade Comanche medicine men object to the newly-signed treaty with Theodore Roosevelt. They are venting their displeasure on two white men who are desecrating tribal territory in Wyoming. Geronimo must protect the men or renege on his agreement with Roosevelt. He offers Doc one year of restored health in exchange for taking on this mission.

Welcome to the birth of American paleontology, spearheaded by two brilliant men, Edward Drinker Cope and Othniel Charles Marsh, two men whose genius is only exceeded by their hatred for each other's guts.

Now, with the aid of Theodore Roosevelt, Cole Younger, and Buffalo Bill Cody, Doc Holliday must save Cope and Marsh not only from the Comanches, not only from living, breathing dinosaurs, but from each other. And that won't be easy.