Geneslide — Richard Quarry

You don't miss your genes till they turn prehistoric.
To save Earth from nuclear holocaust, the Timekeeper must start evolution running backward. And man, is he pissed. So pissed, his entire To-Do list consists of one item: exterminate all traces of humanity back to its primate roots.
As people morph in and out of whatever prehistoric animal their personality fits them for, mankind's last, best hope falls on Galloping Ariadne and Philip the Assault Otter. Grabbing a sort-of Time Machine, the Whatever, from a mad professor, they careen through time at the head of their gallant (well…) band battling everything dinosaurs to Egyptian gods. All to convince the Timekeeper to give primates one last chance.
But hot on their trail comes an alt-right cabal led by a Sabertooth with an ego long as his fangs. He has a Whatever too, and it's even bigger. He doesn't give diddly about the extinction of humanity. Not so long as he ends up at the top of the food chain.
A wild ride up and down the evolutionary tree, Geneslide delivers action, adventure, moral uplift, and a love story literally for the ages between … it's complicated.