Zoofights has featured prehistoric animals before, especially in Zoofights 4 which was roughly half extinct species, and even used one just last year (Murducken), but the ancient past is a rich mine indeed for interesting creatures that could be fitted with various weapons, enhancements, and muscle-bound limbs and sent into battle.
Anomalocaris
This is probably as far back into the past as we could possibly go for new Zoofighters. Anomalocaris lived during the Cambrian period, half a billion years ago. It's an absolutely ancient creature that has no relatives living today. It is believed Anomalocaris could reach six feet in length - small for a zoofighter, but perhaps a genetically enlarged one or a swarm of them could make an impact.
Opabinia
And you thought Anomalocaris looked bizarre. Add three more eyes and change those spiked tentacles to a flexible arm with a spiked claw on the end and you get Opabinia. Sadly, you also have to vastly shrink him down to a size completely unusable for Zoofights. Fire up the growth ray, folks.
Pterygotus
There was a whole family of sea-scorpions once. These relatives of modern scorpions were the biggest, strongest creatures on earth when they first evolved. At a length of eight feet, this is one scorpion that didn't need any poison to survive.
Brontoscorpio
It's a damn crime we still haven't had a scorpion zoofighter. Oh sure, every so often a scorpion tail gets stitched on here or there, but never a full-on scorpion getting in there and kicking some ass. While there's no need to time travel for a scorpion, and Brontoscorpio isn't big enough to be used without a growth hormone or something (about three feet), can you resist anything whose name translates to "THUNDER SCORPION"?
Dunkleosteus
DAMN, SON, LOOK AT THIS BADASS MOTHERFUCKER. 30 FEET LONG. 80,000 TONS OF BITE STRENGTH. I CAN'T BELIEVE MAJOR FAILURE-
Never mind.
