DinoMechs

My name is Michael Claymore, former convicted felon, active duty space marine, and my battle buddy is a dinosaur.
When the histories are studied by those happy few who inherit the galaxy we have left them with, my hope is that they look favorably, perhaps even with a bit of mirth, upon we poor souls who fought side by side with the mighty dinosaurs of Battle Force Jurassic.
The Invaders emerged from somewhere beyond the Milky Way and started conquering everything in sight. They brought with them massive kaiju monsters that made every Godzilla movie pale in comparison. These things would smash through our cities, gobbling up every human being, nuclear plant, or electrical tower they could find. In their wake came legions of alien infantry outfitted with body armor and ray guns, who stalked the ruins looking for survivors.
It was all our modern military could to just to hold them back, and even that cost us dearly. Humanity was in the deep dark stank of it, and some desperate scientists came up with a crazy idea. We needed not only a way to fight back effectively, but a symbol of power to rally around.
When a Tyrannosaurus Rex joins your team, especially one armed with missile launchers and mini-guns, you know it's business time.