Yeah, the Dog-Aliens are a race that had six limbs (two arms, four legs). They stood upright, walking on those four legs. They were incredibly tall, the steps on their stairs went to our waist, forcing humans to climb them with more effort rather than simply walking up them.
Also, Dog-Alien artwork on the floor couldn't be enjoyed by humans as it was designed for a much taller being. Their technology was primarily biological, their buildings and space ships are grown and have actual DNA that Weyland-Yutani collected samples of.
The moon or planetoid alien habitat that the Founders found also belonged to the Dog-Aliens. They used biological slug like creatures to grow technology, the Founders/Rage calls these things Fazes. When they dated the planetoid, it was five million years old.
Their teeth are rather blunt and don't look carnivorous. They seem to have hair on top of their heads but their faces are hairless. They have a dog-like snout hence the name.
Like SM pointed out, they seem to have had bad luck with the Xenomorphs. Both, on LV-178 and on "Midsummer", the five million year old artificial moon that was still growing when the Founders discovered it because the Faze creatures continued working and building. Two Fazes were brought aboard the ships of the Founders and proceeded to modify them into much better and faster ships with staggering advancements.
The ships upgraded became much more biological, also becoming reddish or pinkish in colour in contrast to the black biomechanical look of the Space Jockey and Engineer vessels and architecture.
I also remember an artwork found in one of their buildings depicting them having a public bath among themselves, some even encountering other creatures which were shown in the artworks seen by the humans. I think one of them displayed some kind of farming, I can't remember if that's correct.
