M1M-316
From The Stargate Omnipedia
World in the Pegasus Galaxy. Sergeant Stackhouse reported lush surroundings on this planet, and as far as he could tell it seemed uninhabited. With Dr. Elizabeth Weir's blessing Major John Sheppard and his team scouted the planet for consideration as their Pegasus Galaxy Alpha Site. Unfortunately the unit was driven back to Atlantis by at least one creature that appeared to be a Tyrannosaurus Rex.
KEY EPISODE
The Siege, Part 1 - Sheppard's unit rushes back to Atlantis from M1M-316 after barely escaping the jaws of a dinosaur.