Forerunner fauna and flora

Summary
Native Lifeforms to Halo, possibly only Installation 04. They are both bipedal and quadreped in stature, and somewhat resemble Earth's dinosaurs. These animals are only found in the Halo E3 2000 Trailer. However, the smaller one has been identified as a Blind Wolf in the DVD.

Although they did not make it to the final cut of the game, this does not exactly mean they aren't part of Halo as a whole. Engineers for example didn't make the final cut of Halo either, additionaly they were actually depicted in the Halo Novels. So who knows if these animals are meant to be there, and just unseen. They seem to have been created just to add some more depth to the Halo Mythos.

The Birds of Installation 05
On the levels, Delta Halo, Regret, Gravemind and High Charity. if you look up to the sky (or towards the city for the last 2 levels) you will see strange birds. The first thing you think is they might be dinosaurs that evolved into bird-like things. However, they are seen in some parts when you are on High Charity, and it is also possible that the Covenant brought 'food', and they are seen on 05 because they would breed quickly. Yet again, if they are dinosaurs, the Covenant would bring specimens to their holy city. Basically, it may never be known if they are dinosaurs, or food brought by the Covenant. Bungie may be, very well the only ones to ever know.