Okay, a bit of fair warning to people who come here from Munakata. Hoshino-sensei was originally known for adapting Western sci-fi into manga form and for writing PSEUDOSCIENCE into his original manga. This was also the case with early chapters of Munakata, in which badly outdated or completely baseless pseudohistorical content were prevalent. The later chapters which are much better researched and contain actual academic speculation in the Japanese scholarly community came about after his editor decided to make the series as a whole more respectable by consulting actual historians and folklorists. That's why the more recent second Munakata series is so well-researched despite the still-fantastical nature of the stories themselves.
This manga came from the Hoshino Dark Ages. Anyone with basic knowledge of up-to-date palaeontology will cringe at the horribly outdated contents and the sheer amount of pseudoscience involved in the writing. So if you want to read this, just appreciate the story and forgive the B.S. There is nothing like the quality of research in current Munakata to be found here and the manga actually reads like pulp-era sci-fi stories despite being written in 1991. Good old guilty fun.