It's time for a lesson in Jurassic swag, courtesy of UFC fighter Derrick "The Black Beast" Lewis ... who dropped $125k on the a golden T-Rex motor thingy ... and TMZ Sports has the pics.

Lewis hit up Joseph McCamish of Etune Autosports in Houston and told the man he wanted "the baddest T-Rex he could build" ... and was willing to pay big bucks for it.

We talked to McCamish who tells us his

guys were up to the task and created a one-of-a-kind ride for the Octagon god.

What'd they do? A full air ride system, custom-made leather seats, a black suede steering wheel, JBL audio system, a custom fabricated body kit and the piece de resistance ... a custom gold body wrap.

Final price for the whole thing ... $125k!! 

Beating people up ... it pays really well.