Trog/Versions

Nintendo Entertainment System
Developed by Acclaim Entertainment and Visual Concepts and released in 1991; this version of the game does not feature Rex or Gwen, and the attract mode's intro (implying "Trog" is an individual) was changed from the following, given that it introduced each of the game's four main characters by name and "friends" sort-of rhymes with "Gwen":

LONG, LONG AGO IN A LAND NAMED OG - THERE LIVED A ONE-EYED CAVEMAN BY THE NAME OF TROG! AND IN THAT LAND THERE LIVED FOUR FRIENDS - REX AND BLOOP, SPIKE AND GWEN!

The original manual also continued this poem - and it's not known why the full version didn't make it into the game:

THEY NEED YOUR HELP TO GET HOME, YOU SEE - FOR IF YOU DON'T LEAD THEM TROG'S DINNER THEY'LL BE! WHEN THEY'VE PICKED UP ALL THEIR EGGS, YOU'LL HEAR THEM SCREAM AND SHOUT -  'CAUSE LEADING DINOS HOME IS WHAT THE GAME'S ABOUT!

The first four lines of the poem were the same in the NES version, but the next four were reduced to two as two of the main characters weren't featured:

AND TWO CHARACTERS, VERY MUCH ALIKE, MISCHIEVOUS LITTLE DINO-MITES NAMED BLOOP AND SPIKE!

This version of the game also loses the claymation look of the original (given that it was produced upon a less powerful system than the Midway Y-Unit).

MS-DOS
Developed by Acclaim Entertainment and released in 1991; this version of the game doesn't feature Spike or Gwen, but it does seem to retain the claymation look of the original (unlike the aforementioned NES version), and has joystick support.