Comic Title: Showcase #20
Publisher: DC (National Comics Publications, Inc.)
Address: 575 Lexington Avenue, New York, NY
Cover Date: May/Jun 1959
On Sale Date: March 17, 1959 Newsstand Date March 17, 1959
Source: House Ad, Strange Adventures #104, Page 11

Copyright Date March 17, 1959
Source: Library of Congress, Periodicals 1959

Frequency: Bi-monthly
Cover Price: $0.10
Page Count: 32
Editor: Jack Schiff

Title: "Prisoners of 100 Million B.C."
Pages: 24

Feature(s):
Rip Hunter (of Earth-1)

Writer: Jack Miller
Artist: Ruben Moreira

Reprinted In:
World's Finest Comics #225 (1974)
Showcase Presents:Showcase Vol. 1 TPB (2012)
Showcase Presents:Rip Hunter, Time Master Vol. 1 TPB (2012)

Feature Character(s)

• Rip Hunter (first appearance; last appearance in Justice League of America #144; next appearance in Showcase #21)

Supporting Character(s)

• Jeff Smith (first appearance; last appearance in Justice League of America #144; next appearance in Showcase #21)
• Bonnie Baxter (next appearance in Showcase #21)
• Corky Baxter (next appearance in Showcase #21)

Villain(s)

• Hoyt and Keegan (two small-time crooks; no further appearances)

Comments:
Chap. 2: "The Modern-Day Cavemen"
Chap. 3: "The Great Beast Stampede"

Rip Hunter invents and uses two Time Sphere which allow him and his friends to travel into the past.

Synopsis:
Rip Hunter invents a pair of Time Sphere’s which allow him to travel backwards in time. On the initial voyage, he travels to the Mesozoic Age with his assistant Jeff.

While Rip is gone, criminals break into his lab and force Rip’s friend Bonnie and her younger brother Corky to take the other Time Sphere into the past as well. The Time Sphere is damaged upon arrival stranding Bonnie, Corky, and the criminals. To escape they search for Rip and Jeff. The crooks locate Rip’s time sphere and hide it, then they fall into a river and are swept away.

Rip and his companions begin looking for the hidden time sphere, braving the dangers of dinosaurs and an erupting volcano to find it. When they do find it, the crooks return, so Rip takes replacement parts from the Sphere, then sends Bonnie and Corky back to the present. Rip, Jeff, and the crooks find and repair the other Time Sphere and escape a dinosaur stampede before returing to their own time period.