Here's a link to Tonnies' cryptoterrestrial book. Unfortunately, he passed away at a young age and only published a few books. But his take was always quite intriguing:
https://www.amazon.com/dp/B004J176GC/ref=dp-kindle-redirect?\_encoding=UTF8&btkr=1
John Keel posited this back in the 60s and was roundly rejected by the "Space Brothers" crowd.
Mac Tonnies wrote a book on the subject: