Back to the Stone Age

From Author Wars - https://authorwars.com/publications/back-to-the-stone-age-731565.html

Overview:

Title: Back to the Stone Age
Author: Edgar Rice Burroughs
Year: 1978
ISBN-10: 0441046363
Publisher: Ace Books
Price: $1.95
Pages: 251
Binding: Paperback
Type: Novel
Title Reference: Back to the Stone Age
Notes:
"Fourth Ace printing: January, 1973" - which is likely a holdover from an earlier printing. Original title: Seven Worlds to Conquer on title page and cover "Cover painting by Frank Frazetta", the artwork is also signed