Flint the Time Detective

Flint the Time Detective (時空探偵ゲンシクン, Jikū Tantei Genshi-kun), is a Japanese manga series by Hideki Sonoda and Akira Yamauchi and was published by Bros. Comics in Japan. A second manga by Bom Bom Comics was also produced and was released as a special promo for the anime adaptation, which aired from 1998 to 1999. In the US, the dubbed version aired from March 5 to November 5, 2000 on Fox Kids.

Plot
In the 25th century, a dark lord has 'infected' history with time-devices that could damage history beyond repair. A caveboy named Genshi and his father lived in the stone ages when they got turned into fossils along with a time monster named Lovelove. They are discovered by the Yamato siblings, Tokio and Sora who brought them to their father, reviving them to the present era. After defending Lovelove from a trio led by T.P. Lady, the Space and Time Bureau admit Genshi as a time detective. Along with Tokio and Sora, they travel through time to bring the remaining time monsters and save history.