Dom'Kavash

The Dom'Kavash were a mysterious race that existed around the post-Cretaceous period who were responsible for a majority of alien artifacts as well as the Nomads found within the Sirius Sector (and likely other sections of their vast empire). Nothing is known about their physiology, but little more is known about their culture. They disappeared mysteriously millions of years before mankind evolved, for unknown reasons.

Speculation
There is speculation over whether or not the Omega 41 System having gone nova had anything to do with the extinction of the Dom'Kavash. If so, it is believed that it caused a wave of radiation that wiped them out. However, no skeletons or remains of any kind have ever been procured, perhaps suggesting that they were invertebrate in nature. Most of their architecture found in ruins described as being Dom'Kavashi in nature have an outwardly primitive look, although this may in fact be due to the sheer length of time since their abandonment as opposed to actual design style.