If you're looking for manga similar to Genjuu Jiten, you might like these titles.
He's small, he's scaly, he's Gon! This tiny dinosaur may seem like nothing but a lazy reptile that lounges around and causes mischief, but he's also a pint-sized powerhouse filled with energy who can defend himself when the right kind of food is involved. Whether he's riding a lion like a horse, stealing fish from the mouth of a giant shark or playing house with a group of penguins, Gon manages to get into trouble on every adventure he takes.
In the prehistoric era, an unconscious woman is discovered by a family of foragers. In need of a bride, the eldest son (who looks like a girl) decides to marry her. Hunting mammoths, singing, dancing, taking naps, and occasionally going to hot springs; this is the daily life of stone-age people who are living comfortably in the period just before the Ice Age.
Johnathan Perkins, son of Vietnam War hero "Perky" Perkins, is an U.S. exchange officer serving in British Special Air Service (SAS). He and Sergei, a Russian Spetsnaz exchange officer, participate covert SAS actions behind enemy lines alongside British soldiers in Operation Desert Storm.